Title of Invention	PRINTABLE MEDIUM FOR THE ETCHING OF SILICON DIOXIDE AND SILICON NITRIDE LAYERS
Abstract	A printable etching medium in the form of a paste for etching and optionally doping inorganic glass-like or crystalline layers selected from the group of glasses based on silicon dioxide and the glasses based on silicon nitride, which are located on crystalline or amorphous silicon surfaces, comprising a) an etching component b) solvent c) polymer particles having a relative particle diameter in the range from 10 nm to 50 µm, d) optionally a homogeneously dissolved organic thick-ener e) optionally at least one inorganic and/or organic acid, f) optionally an additive and g) optionally inorganic particles, said medium having a viscosity at 20° C. in the range from 6 to 35 Pa*s at a shear rate of 25 s-1.

Title of Invention

PRINTABLE MEDIUM FOR THE ETCHING OF SILICON DIOXIDE AND SILICON NITRIDE LAYERS

Abstract

A printable etching medium in the form of a paste for etching and optionally doping inorganic glass-like or crystalline layers selected from the group of glasses based on silicon dioxide and the glasses based on silicon nitride, which are located on crystalline or amorphous silicon surfaces, comprising a) an etching component b) solvent c) polymer particles having a relative particle diameter in the range from 10 nm to 50 µm, d) optionally a homogeneously dissolved organic thick-ener e) optionally at least one inorganic and/or organic acid, f) optionally an additive and g) optionally inorganic particles, said medium having a viscosity at 20° C. in the range from 6 to 35 Pa*s at a shear rate of 25 s-1.

Full Text	Printable medium for the etching of silicon dioxide and silicon nitride layers The present invention relates to a novel printable etching medium having non-Newtonian flow behaviour for the etching of surfaces in the produc- tion of solar cells, and to the use thereof. The present invention furthermore also relates to etching and doping media which are suitable both for the etching of inorganic layers and for the doping of underlying layers. In particular, these are corresponding particle-containing compositions by means of which extremely fine structures can be etched very selectively without damaging or attacking adjacent areas. The problem of structuring oxide layers on a support material arises, for example, in the production of solar cells. A crystalline silica solar cell usually consists of a p-conducting substrate into which a layer of an n- conducting substance, for example phosphorus, of uniform thickness is diffused on the front side. A metallically conducting contact is applied to the front and reverse sides of the wafer for conduction of the current pro- duced on incidence of light. With regard to an inexpensive production process which is suitable for mass production, the contact is usually pro- duced by screen printing. Besides the oxide layers that have to be structured during solar cell pro- duction, silicon nitride layers also have to be etched. For the etching of corresponding nitride layers, the methods used have to be modified and the etching pastes adapted in a suitable manner. 1. Prior art and object of the invention The surfaces of crystalline silicon solar cells are coated with thin inorga- nic layers during the production process, and optionally also after the end thereof. These layers have thicknesses in the range from 20 to 200 nm, in most cases in the range from 50 to 150 nm. Duririg the process for the production of crystalline silica solar cells, it is therefore advantageous in a number of process steps to etch fine lines into these inorganic layers of the solar cell; These openings in the surface of the solar cell can be used, for example, for the production of a so-called selective emitter, also known as 2-stage emitter. To this end, a high degree of n-doping, preferably by means of phosphorus diffusing in, is produced in a subsequent diffusion step in the partial openings of a diffusion barrier located on the silicon. In the present description, inorganic surfaces is taken to mean oxidic and nitride-containing compounds of silicon, in particular silicon oxide and silicon nitride surfaces. The mode of action of such diffusion barriers is known to the person skilled in the art and is described in the literature [A. Goetzberger; B. VoB; J. Knobloch, Sonnenenergie: Photovoltaik [Solar Energy: Photovoltaics], Teubner Studienbucher Stuttgart 1997, pp 40; 107]. These diffusion barriers can be produced in a variety of ways: Very dense silicon dioxide layers are obtained, for example, by heat treatment of silicon in an oxygen-containing atmosphere at temperatures in the region of 900°C (thermal oxide). Also known to the person skilled in the art is the deposition of silicon di- oxide by the CVD process. Depending on the way the reaction is carried out, a distinction is made here between, inter alia, the following proc- esses: - APCVD (atmospheric pressure CVD) - PE-CVD (plasma enhanced CVD) - LP-CVD (low pressure CVD) A common feature of these processes is that the desired inorganic com- pound is obtained from the gas phase of a volatile precursor, for example silane (SiH4) or TEOS (tetraethyl orthosilicate) in the case of silicon di- oxide, by deposition of the precursor on the target substrate with decom- position. Silicon dioxide layers which form a diffusion barrier can also be obtained by means of wet-chemical coating with a liquid or dissolved solid precur- sor in a solvent or solvent mixture. These liquid systems are usually ap- plied to the substrate to be coated by spin coating. These systems are known to the person skilled in the art as spin-on-glass (SOG). In many cases, the SiO2 layer applied also remains as reflection-reducing passivation layer. This is particularly frequently the case for thermally grown SiO2. Silicon nitride layers are used less as diffusion barriers in the art of crys- talline solar cells, although they are in principle likewise suitable for this purpose. Silicon nitride layers are mainly used as passivation and anti- reflection layers. It is also advantageous in the production of crystalline silicon solar cells to be able to produce openings in a targeted manner in the silicon nitride layers. An example which may be mentioned here is the application of electrically conductive pastes. These metal pastes are usually "fired through" the silicon nitride layer at temperatures in the region of 600°C, facilitating an electrical contact to the emitter layer. Due to the high tem- peratures, polymer-based (epoxy or phenolic resin) metallisation pastes cannot be used. Crystal defects and metallic contamination in the under- lying silicon also arise in the "fire-through process". Due to the system, the passivation layer is additionally completely destroyed by the overlying printed-on metal paste. A partial, narrower opening of the silicon nitride layer for electrical contacting would be more advantageous, with retention of the passivation layer in the edge regions, which are covered by the overlying metallisation layer. Besides the pure diffusion barriers consisting of silicon dioxide or silicon nitride, it is also possible to use thin glass layers in the production of crystalline silicon solar cells. Definition of glass: Glass is taken to mean per se a homogeneous material, for example quartz, window glass, borosilicate glass, and also thin layers of these materials produced on other substrates (for example ceramics, metal sheets, silicon wafers) by various processes known to the person skilled in the art (CVD, PVD, spin-on, thermal oxidation, inter alia). Glasses below is taken to mean silicon oxide- and silicon nitride-con- taining materials which are in the solid amorphous physical state without crystallisation of the glass components and which have a high degree of structural disorder in the microstructure owing to the lack of long-range order. Besides pure SiO2 glass (quartz), all glasses (for example doped glasses, such as borosilicate, phosphosilicate, borophosphosilicate glasses, coloured, milk and crystal glasses, optical glasses) which con- tain SiO2 and other components, in particular elements such as, for ex- ample, calcium, sodium, aluminium, lead, lithium, magnesium, barium, potassium, boron, beryllium, phosphorus, gallium, arsenic, antimony, lanthanum, zinc, thorium, copper, chromium, manganese, iron, cobalt, nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, sil- ver, cerium, caesium, niobium, tantalum, zirconium, neodymium, praseo- dymium, which occur in the glasses in the form of oxides, carbonates, nitrates, phosphates, sulfates and/or halides or function as doping ele- ments in the glasses, are covered. Doped glasses are, for example, borosilicate, phosphosilicate, borophosphosilicate, coloured, milk, crystal glasses and optical glasses. The silicon nitride may likewise comprise other elements, such as boron, aluminium, gallium, indium, phosphorus, arsenic or antimony. Definition of silicon oxide- and silicon nitride-based systems: Silicon oxide-based systems are defined below as all crystalline systems which do not fall under the definition of amorphous SiO2 glasses given above and are based on silicon dioxide; these can be, in particular, the salts and esters of orthosilicic acid and condensation products thereof- generally known as silicates by the person skilled in the art - as well as quartz and glass-ceramics. Furthermore, other silicon oxide- and silicon nitride-based systems, in particular the salts and esters of orthosilicic acid and condensation prod- ucts thereof, are encompassed. Besides pure SiO2 (quartz, tridymite, cristobalite), all SiO2-based systems built up from SiO2 or "discrete" and/or linked [SiO4] tetrahedra, such as, for example, mesosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, tectosilicates, and other components, in particular elements/components such as, for example, calcium, sodium, aluminium, lithium, magnesium, barium, potassium, beryllium, scandium, manganese, iron, titanium, zirconium, zinc, cerium, yttrium, oxygen, hydroxyl groups, halides, are also encom- passed. Silicon nitride-based systems are defined below as all crystalline and partially crystalline (usually referred to as microcrystalline) systems which do not fall under the definition given above for the amorphous silicon nitride glasses/layers. These include Si3N4 in its α-Si3N4 and β-Si3N4 modifications and all crystalline and partially crystalline SiNx and SiNx:H layers. Crystalline silicon nitride may comprise other elements, such as boron, aluminium, gallium, indium, phosphorus, arsenic and antimony. Etching of structures The use of etchants, i.e. chemically aggressive compounds, results in the dissolution of the material exposed to the etchant attack. In most cases, the aim is completely to remove the layer to be etched. The end of the etching is reached by the encountering of a layer which is substantially resistant to the etchant. In addition, there is the process known to the person skilled in the art of partial removal of a layer by etching to a target thickness which is usually defined. Etching of structures on silicon oxide- and silicon nitride-based glasses and other silicon oxide- and silicon nitride-based systems: According to the current state of the art, any desired structures can be etched selectively in silicon oxide- and silicon nitride-based glasses and other silicon oxide- and silicon nitride-based systems or surfaces thereof and layers thereof of variable thickness directly by laser-supported etch- ing methods or, after masking, by wet-chemical methods ([1] D.J. Monk, D.S. Soane, R.T. Howe, Thin Solid Films 232 (1993), 1; [2]J. Buhler, F.- P. Steiner, H. Baltes, J. Micromech. Microeng. 7 (1997), R1) or by dry- etching methods ([3] M. Kohier "Atzverfahren fur die Mikrotechnik" [Etch- ing Methods for Microtechnofogy], Wiley VCH 1983). In the laser-supported etching methods, the laser beam scans the entire etching pattern on the glass dot by dot or line by line in the case of vec- tor-orienting systems, which, besides a high degree of precision, also requires considerable adjustment effort and time. The wet-chemical and dry-etching methods include material-intensive, time-consuming and expensive process steps. A. Masking of the areas not to be etched, for example by: » Photolithography: Production of a negative or positive of the etching structure (depending on the resist), coating of the substrate surface (for example by spin-coating with a liquid photoresist), drying of the photoresist, exposure of the coated substrate surface, development, rinsing, optionally drying B. Etching of the structures by: • dip methods (for example wet etching in wet-chemistry benches): dip- ping of the substrates into the etching bath, etching operation, re- peated rinsing in H2O cascade sinks, drying • spin-on or spray methods: the etching solution is applied to a rotating substrate, the etching operation can be carried out without/with input of energy (for example IR or UV irradiation), this is followed by rinsing and drying • dry-etching methods, such as, for example, plasma etching, in expen- sive vacuum units or etching with reactive gases in flow reactors C. Removal of the photoresist: in the final process step, the photoresist covering the protecting areas of the substrate must be removed. This can be carried out by means of sol- vents, such as, for example, acetone, or dilute aqueous alkaline solu- tions. The substrates are finely rinsed and dried. Full-area etching of silicon oxide- and silicon nitride-based glasses and other silicon oxide- and silicon nitride-based systems: In order to etch silicon oxide- and silicon nitride-based glasses and other silicon oxide- and silicon nitride-based systems and layers of variable thickness thereof over the entire area completely or only to a certain depth, use is predominantly made of wet-etching methods. The silicon oxide- and silicon nitride-based glasses and other silicon oxide- and sili- con nitride-based systems and layers of variable thickness thereof are dipped into etching baths, which usually contain the toxic and highly caustic hydrofluoric acid and optionally additives of other mineral acids. The disadvantages of the etching methods described lie in the time-con- suming, material-intensive and expensive process steps which are in some cases complex in technological and safety terms and are frequently carried out discontinuously. International Application WO 01/83391 A describes etching media in the form of printable, homogeneous, particle-free etching pastes having non- Newtonian flow behaviour for the etching of inorganic, glass-like amor- phous or crystalline surfaces, in particular of glasses or ceramics, pref- erably SiO2- or silicon nitride-based systems, and the use of these etch- ing media. In particular on printing of surfaces, use of these particle-free media gave rise to problems due to inadequate resilience of the printed lines, dots or structures (inadequate structure fidelity), meaning that a significant broadening of the originally printed lines occurs (bleeding of the etching species on the substrate). US 5,688,366 A uses particle-containing etching pastes for the etching of a transparent conductive layer (for example ITO). The etching pastes used are prepared from molten iron chloride containing water of crystalli- sation, glycerol and polymer particles. These compositions are suitable for the etching of lines having a width of about 1 mm. Experiments have shown that these etching pastes are not suitable for the etching of very thin lines having a width of less than 1 mm cleanly and without flaws, ir- respective of whether polymer particles having a diameter of 0.01 µm or of 30 µm are employed for the preparation of the pastes. Objective The object of the present invention is therefore to provide novel, inexpen- sive etching pastes for the etching of very uniform, thin lines having a width of less than 100 µm, in particular of less than 80 µm, and of micro- fine structures on silicon dioxide and/or silicon nitride layers which are lo- cated on silicon solar cells. A further object of the present invention is to provide novel etching media which can be removed from the treated sur- faces after the etching under the action of heat in a simple manner with- out leaving residues. 2. Description of the invention More recent experiments have now shown that, in contrast to previous experience, the printing properties of etching pastes can advantageously be improved if suitable, selected polymer particles are added. In this con- nection, polymer particles which form a network in the prepared pastes through physical interaction and/or chemical reaction with the other con- stituents of the medium, simultaneously causing an increase in the visco- sity of the composition, have proven particularly suitable. Entirely unex- pectedly, the added particles also contribute to an improvement in the printability of the medium. Given a suitable choice of the added particulate components, it may even be possible to omit entirely the addition of a thickener, which is usually homogeneously distributed in known particle-free pastes. The object of the present application is therefore achieved by the provi- sion of a novel printable etching medium having non-Newtonian flow be- haviour in the form of an etching paste for the etching of inorganic, glass- like or crystalline surfaces selected from the group of glasses based on silicon oxide and glasses based on silicon nitride, which comprises polymer particles consisting of a material selected from the group of polystyrene, polyacryl, polyamide, polyimide, polymeth- acrylate, melamine, urethane, benzoguanine, phenolic resin, silicone resin, fluorinated polymers (PTFE, PVDF, inter alia) and micronised wax, in the presence of an etching component, solvent, thickener, optionally at least one inorganic and/or organic acid, and optionally additives, such as antifoams, thixotropic agents, flow-control agents, deaerators, adhesion promoters. The etching medium according to the invention is effective even at temperatures of 15 to 50°C or can optionally be activated by in- put of energy. Preferred forms of the pastes according to the invention and use thereof arise from Claims 2-18. The present invention further- more relates to a process for the etching and optionally for the simulta- neous doping of inorganic, glass-like, crystalline surfaces according to Claims 29 and 33. Claim 28 relates to particular embodiments of the use of the etching pastes according to the invention. 3. Detailed description of the invention In accordance with the invention, the novel etching pastes having thixo- tropic, non-Newtonian properties are used to structure silicon dioxide or nitride layers in a suitable manner during the process for the production of products for photovoltaics, semiconductor technology, high-perform- ance electronics, of solar cells or photodiodes. To this end, the paste is printed in a single process step onto the surface to be etched and re- moved again after a pre-specified reaction time. In this way, the surface is etched and structured in the printed areas, while unprinted areas re- main in the original state. The surface to be etched here can be a surface or part-surface of silicon oxide- or silicon nitride-based glass and other silicon oxide- and silicon nitride-based systems, and/or a surface or part-surface of a porous and 1 > non-porous layer of glass and other silicon oxide- and silicon nitride- based systems on a support material. A suitable process having a high degree of automation and having high throughput utilises printing technology for the transfer of the etching paste to the substrate surface to be etched. In particular, the screen, pad, stamp, ink-jet printing processes are printing processes that are known to the person skilled in the art. Manual application is likewise possible. Depending on the screen, plate or stamp design or cartridge addressing, it is possible to apply the printable, homogeneous, particle-free etching pastes having non-Newtonian flow behaviour which are described in ac- cordance with the invention over the entire area or selectively in accor- dance with the etch structure pattern only in the areas where etching is desired. All masking and lithography steps which are otherwise neces- sary are thus superfluous. The etching operation can be carried out with or without energy input, for example in the form of heat radiation (using IR lamps). The actual etching process is subsequently completed by washing the surfaces with water and/or a suitable solvent. More precisely, the print- able, polymer particle-containing etching pastes having non-Newtonian flow behaviour are rinsed off the etched areas using a suitable solvent after etching is complete. Use of the etching pastes according to the invention thus enables long runs to be etched inexpensively on an industrial scale in a suitable, automated process. In a preferred embodiment, the etching paste according to the invention has a viscosity in the range from 10 to 500 Pas, preferably from 50 to 200 Pas. The viscosity is the material-dependent component of the fac- tional resistance which counters movement when adjacent liquid layers are displaced. According to Newton, the shear resistance in a liquid layer between two sliding surfaces arranged parallel and moved relative to one another is proportional to the velocity or shear gradient G. The propor- tionality factor is a material constant which is known as the dynamic vis- cosity and has the dimension m Pa.s. In Newtonian liquids, the propor- tionality factor is pressure- and temperature-dependent. The degree of dependence here is determined by the materia! composition. Liquids or substances having an in homogeneous composition have non-Newtonian properties. The viscosity of these substances is additionally dependent on the shear gradient. For the etching of fine structures, having line widths of printed etching media,it has now been found to be particularly advanta- geous to thicken etching media completely or partially using finely divided particulate systems instead of particle-free etching pastes comprising a homogeneously distributed polymer (types see WO 01/83391 A) for thickening. Particularly suitable for this purpose are polymer particles which interact with the other components of the composition and form a network by means of chemical bonds or a purely physical interaction at the molecular level. The relative particle diameters of these systems can be in the range from 10 nm to 30 urn. Corresponding polymer particles having a relative particle diameter in the range from 1 to 10 µm have proved particularly advantageous. Particles which are particularly suitable for the purpose according to the invention can consist of the following materials: - polystyrene - polyacryl - polyamide - polyethylene - ethylene-vinyl acetate copolymer - ethylene-acrylic acid-acrylate terpolymer - ethylene-acrylate-maleic anhydride terpolymer - polypropylene - polyimide - polymethacrylate - melamine, urethane, benzoguanine, phenolic resin - silicone resin - fluorinated polymers (PTFE, PVDF), and - micronised waxes The use of a very finely divided polyethylene powder, which is, for exam- ple, currently marketed by DuPont PolymerPowders Switzerland under the trade name COATHYLENE HX® 1681, having relative particle dia- meters d50 value of 10 µm, has proven particularly suitable in the experi- ments. These particulate thickeners can be added to the etching medium in amounts of 1 to 50% by weight, advantageously in the range from 10 to 50% by weight, in particular from 25 to 35% by weight. Also suitable in principle are particulate polymeric thickeners based on - polystyrene - polyacryl - polyamide - polyimide - polymethacrylate - melamine, urethane, benzoguanine, phenolic resin - silicone resin. Compared with the particle-free etching pastes described in WO 01/83391 A, the addition of the particulate thickeners according to the invention has enabled the following improvements to be achieved: I. Particulate thickening results in improved resilience of the etching medium. The particles form a skeleton-structure in the etching me- dium. Similar structures are known to the person skilled in the art from highly dispersed silicic acid (for example Aerosil®). In particular in screen printing of the etching pastes, a broadening of the printed structures due to flow can be substantially prevented or at least greatly restricted by the present invention. The printed, and thus paste-covered area therefore corresponds substantially to the area specified in the screen layout. Many inorganic particles, such as, for example, silicic acid or modified silicic acid, cannot be employed for thickening the etching medium owing to their reactivity with the etch- ing component employed. For example, a chemical reaction of silicic acid with NH4HF2 takes place if the latter serves as etching compo- nent. II. With the aid of particulate thickening, lines of greater print height with retained width are, in addition, printed on use of the same screen or mask than on use of corresponding particle-free pastes, as de- scribed, for example, in WO 01/83391 A. This simultaneously results in a greater application rate of etching component per unit area. If relatively thick silicon dioxide or silicon nitride layers (> 100 nm) are to be etched, this is a particular advantage for complete etching. III. The more pronounced non-Newtonian or thixotropic properties of the etching paste have a particularly advantageous effect for screen printing and result in considerably improved results. In particular, this is evident in a shortened etching time or an increased etching rate for the same etching time and especially in a greater etching depth in the case of relatively thick layers. IV. The thickening associated with the addition of polymer particles ac- cording to the invention results in a considerably lower binding capa- city of the etching paste. Given a specific choice of the particles added, an increased etching rate and thus a considerably increased etching depth are, surprisingly, achieved for the same amount of added etching component. V. The significantly greater print height achieved under the same printing conditions, i.e. on use of the same screen and the same printing parameters, furthermore causes significantly delayed drying of the printed etching species. This enables the etching species to act on the substrate for longer. It is particularly important in the case of accelerated etching under elevated temperatures. In addition, the material remaining after the etching process can be removed significantly more easily in the final cleaning process. Significant improvements in the present compositions arise; in particular, through a considerably improved screen-printing behaviour, enabling continuous printing of surfaces to be treated without interruptions.The use of the etching pastes according to the invention enables considerably finer etching structures since the pastes have greater viscosities on addi- tion of the same amounts of thickener in the presence of polymer parti- cles. This enables the pastes to be applied in printing with a higher paste layer and consequently for the layers to be etched deeper. The improved rinsing behaviour (wafer cleaning) after etching also shortens the time required for subsequent cleaning. Surprisingly, experiments have shown that the addition of corresponding fine polymer particles also has an advantageous effect in processes for the selective etching of inorganic surfaces for the production of selective emitter structures in solar cells, in which, besides etching, specific phos- phorus doping for the production of n++ regions is also desired. Corre- sponding etching and doping pastes are described, for example, in WO 03/034504 A1. In contrast to the pure etching pastes, these pastes, after application to the wafer surfaces to be etched, are heated over the entire surface or locally depending on the particles present in the paste to tem- peratures in the range from 250 to 350°C for from 30 to 120 seconds and optionally, for additional n++ doping, to temperatures >800°C, in particular to temperatures in the range from 800 to 1050°C, for 20 - 40 minutes. The selected temperature is of course set in such a way that changes in the particles present in the paste do not give rise to any disadvantages. Corresponding etching media may comprise the various forms of phos- phoric acid or suitable phosphoric acid salts or compounds, which are decomposed to the corresponding phosphoric acid on heating, as etching and as doping components. It has been found that orthophosphoric acid, metaphosphoric acid, pyro- phosphoric acid and salts thereof and here in particular the ammonium salts ((NH4)2HPO4, NH4H2PO4, (NH4)3PO4) and other compounds which form one of these compounds on thermal decomposition are capable of completely etching away silicon nitride layers having a layer thickness of 70 mm within a few seconds to minutes at temperatures above 250°C. At 300°C, the etching time is about 60 seconds. For the preparation of the particle-containing media according to the in- vention, the solvents, etching components, thickeners, particles and ad- ditives are mixed successively with one another and stirred for a suffi- cient time until a viscous paste having thixotropic properties has formed. The stirring can-be carried put with warming to a suitable temperature. The, components are usually stirred with one another at room tempera- ture. Preferred uses of the printable etching pastes according to the invention arise for the described processes for the structuring of oxide layers ap- plied to a support material, for the production of solar cells having a se- lective emitter layer on the light incidence side and for the production of solar cells having a selective emitter layer on the light incidence side and a back-surface field on the back. For application of the pastes to the areas to be treated, the etching pastes can be printed through a fine-mesh screen which contains the print template (or etched metal screen). In a further step, the pastes can be baked in the screen-printing process by the thick-layer method (screen printing of conductive metal pastes), enabling the electrical and mechanical properties to be fixed. On use of the etching pastes according to the invention, the baking (firing through the dielectric layers) can instead also be omitted and the applied etching pastes washed off with a suitable solvent or solvent mixture after a certain reaction time. The etching action is terminated by the washing-off. Particularly suitable printing methods are essentially screen printing with screen separation or stencil printing without separation. In screen print- ing, the separation a of a screen is usually several hundred µm with a tilt angle a between the edge of the squeegee, which pushes the etching printing paste over the screen, and the screen. The screen is held by a screen frame, while the squeegee is passed over the screen at a squee- gee velocity v and a squeegee pressure P. In the process, the etching paste is pushed over the screen. During this operation, the screen comes into contact with the substrate in the form of a line over the squeegee width. The contact between screen and substrate transfers the vast ma- jority of the screen printing paste located in the free screen meshes onto the substrate. In the areas covered by the screen meshes, no screen printing paste is transferred onto the substrate. This enables screen print- ing paste to be transferred in a targeted manner to certain areas of the substrate. After the end of the movement E, the squeegee is raised off the screen. The screen is tensioned uniformly using a screen stretcher with hydrau- lic/pneumatic tension and clamping device. The screen tension is moni- tored by defined sag of the screen in a certain area at a certain weight using a dial gauge. With specific pneumatic/hydraulic printing machines, the squeegee pressure (P), the printing velocity (V), the off-contact dis- tance (A) and the squeegee path (horizontal and vertical, squeegee an- gle) can be set with various degrees of automation of the working steps for trial and production runs. Printing screens used here usually consist of plastic or steel-wire cloth. It is possible for the person skilled in the art to select cloths having different wire diameters and mesh widths, depending on the desired layer thick- ness and line width. These cloths are structured directly or indirectly us- ing photosensitive materials (emulsion layer). For the printing of extreme- ly fine lines and in the case of requisite high precision of successive prints, it may be advantageous to use metal stencils, which are likewise provided directly or indirectly with a hole structure or line structure. In order to carry out the etching, an etching paste, as described, for ex- ample, in Example 1, is prepared. Using an etching paste of this type, a thermal SiO2 having a thickness of approx. 100 nm can be removed se- lectively within 60 seconds at 50°C after screen printing. The etching is subsequently terminated by dipping the Si wafer into water and then rinsing with the aid of a fine water spray. For the production of solar cells, wafers comprising p-doped Pz silicon having orientation, for example, are selected. In these, a short, basic etching enables a structure to be produced on the surface which improves the light incidence geometry for reducing reflections. A thin dopant coating film comprising a boron-containing compound can be spin-coated onto the back and dried. The wafers prepared in this way are placed in a tray and introduced into an oven pre-heated to 1000 to 1100°C. An oxygen atmosphere is established in the oven, so that an oxide layer forms directly on all wafer surfaces that are not covered by the boron dopant coating film. At the same time, boron is expelled from the dopant coating film and diffuses into the back of the wafers. p+-doped regions with a depth of approx. 1 to 5 µm form. This embodiment of a solar cell is known to the person skilled in the art under the term "back- surface field". The oxide layers formed on the front can now be structured using the etching pastes described above. For example, these oxide layers can be formed as masks for high n+- phosphorus dopings for the formation of selective emitter layers, while significantly less n+-doping is aimed at in the masked areas. After opening of the pn junction, which would result in short circuits in the solar cell, for example by plasma etching or opening using a LASER beam, the electrical contacts are applied to the front and back of the cell. This can be carried out by means of two successive screen-printing steps using a paste, which may, besides the binders and oxidic additives, com- prise conductive silver particles and/or aluminium. After the printing, the printed contacts are baked at about 700 to 800°C. The present description enables the person skilled in the art to use the invention comprehensively. If anything is unclear, it goes without saying that the cited publications and patent literature should be used. Corre- spondingly, these documents are regarded as part of the disclosure con- tent of the present description. 4. Examples For better understanding and in order to illustrate the invention, ex- amples are given below which are within the scope of protection of the present invention. These examples also serve to illustrate pos- sible variants. Owing to the general validity of the inventive principle described, however, the examples are not suitable for reducing the scope of protection of the present application to these alone. The temperatures given in the examples are always in °C. It further- more goes without saying that the added amounts of the components in the composition always add up to a total of 100% both in the description and in the examples. Example 1 , Etching paste consisting of homogeneous and particulate thickeners To a solvent mixture consisting of 15 g of ethylene glycol monobutyl ether 15 g of triethylene glycol monomethyl ether 29 g of polycarbonate are added successively with stirring 72 g of formic acid (100%) and 46 g of ammonium hydrogen difluoride solution 35%. Then 46 g of polyvinylpyrrolidone (PVP) K-120 are slowly added in portions to the solution with vigorous stirring, and the mixture is stirred for a further 30 minutes. The clear paste pre-thickened with a homogeneous thickener (PVP) is then mixed with 60 g of Vestosint 2070 and the mixture is stirred for a further 2 hours. The paste, which is now ready to use, can be printed using a 280 mesh stainless-steel cloth screen. In principle, polyester or similar screen ma- terials can also be used. Example 2 Etching paste consisting of a particulate thickener to a solvent mixture consisting of 15 g of ethylene glycol monobutyl ether 15 g of triethylene glycol monomethyl ether 29 g of polycarbonate are added successively with stirring 72 g of formic acid (100%) and 46 g of ammonium hydrogen difluoride solution 35%. The clear homogeneous mixture is then mixed with 100g of Vestosint 2070, and the mixture is stirred for a further 2 hours. The paste, which is now ready to use, can be printed using a 280 mesh stainless-steel cloth screen. In principle, polyester or similar screen ma- terials can also be used. The etching paste prepared has proven to be stable on storage over a long time with retention of the advantageous etching properties. Further examples of compositions according to the invention having ad- vantageous properties are given in the following tables: Further examples of compositions according to the invention having ad- vantageous properties for the etching of SiNx are given in the following tables. Comparative Example: Etching paste without particulate additives For a comparative test, the following pressure and etching parameters were used: Screen: steel screen having a mesh count of 280 mesh/inch and a filament diameter of 25 µm and an emulsion thickness of 15 urn. Layout: 100 µm lines Screen printing machine: EKRA E1 Wafers: single-crystal silicon wafers, with 100 nm thermal SiO2 Etching: heated at 50°C for 30 s Result: Line width after etching and rinsing: about 180 µm on average Comparative Example: Etching paste with particulate additives For a comparative test, the following pressure and etching parameters were used: Screen: steel screen having a mesh count of 280 mesh/inch and a filament diameter of 25 µm and an emulsion thickness of 15 urn. Layout: 100 pm lines Screen printing machine: EKRA E1 Wafers: single-crystal silicon wafers, with 100 nm thermal SiO2 Etching: heated at 50°C for 30 s Result: The etched line had a width of 105 µm on average. We Claim: 1. A printable etching medium in the form of a paste for etching and optionally doping inorganic glass-like or crystalline layers selected from the group of glasses based on silicon dioxide and the glasses based on silicon nitride, which are located on crystalline or amorphous silicon surfaces, comprising a) an etching component b) solvent c) polymer particles having a relative particle diameter in the range from 10 nm to 50 urn, d) optionally a homogeneously dissolved organic thick-ener e) optionally at least one inorganic and/or organic acid, f) optionally an additive and g) optionally inorganic particles, said medium having a viscosity at 20° C. in the range from 6 to 35 Pas at a shear rate of 25 s-1. 2. A printable etching medium as claimed in claim 1, wherein the polymer particles have a relative particle diameter in the range from 100 nm to 30 µm. 3. A printable etching medium as claimed in claim 1, comprising polymer particles in an amount of 1 to 80% by weight, based on the total amount of medium. 4. A printable etching medium as claimed in claim 1, comprising polymer particles in an amount of 10 to 50% by weight based on the total amount of medium. 5. A printable etching medium as claimed in claim 1, wherein the etching component is present in an amount of 12 to 30% by weight based on the total amount of medium. 6. A printable etching medium as claimed in claim 1, wherein the thickener is present in an amount of 3 to 20% by weight, based on the total amount of medium. 7. A printable etching medium as claimed in claim 1, comprising one or different forms to phosphoric acid, phosphoric acid salts or compounds which are decomposed to the corresponding phosphoric acid on heating and act as etching and as doping components. 8. A printable etching medium as claimed in claim 1 for surfaces of glasses which comprise elements selected from the group of calcium, sodium, aluminium, lead, lithium, magnesium, barium, potassium, boron, beryllium, phosphorus, gallium, arsenic, antimony, lanthanum, scandium, zinc, thorium, copper, chromium, manganese, iron, cobalt, nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, silver, cerium, caesium, niobium, tantalum, zirconium, yttrium, neodymium and praseodymium. 9. A printable etching medium as claimed in claim 1, comprising as etching component, at least one fluorine compound selected from the group of ammonium, alkali metal and antimony fluorides, ammonium, alkali metal and calcium bifluorides, alkylated ammonium and potassium tetrafluoroborates and/or optionally at least one inorganic mineral acid selected from the group of hydrochloric acid, phosphoric acid, sulfuric acid and nitric acid and/or optionally at least one organic acid, which may contain a straight- chain or branched alkyl radical having 1-10 C atoms, selected from the group of the alkylcarboxylic acids, the hydroxycarboxylic acids and the dicarboxylic acids. 10. A printable etching medium as claimed in claim 9, comprising an organic acid selected from the group of formic acid, acetic acid lactic acid and oxalic acid. 11. A printable etching medium as claimed in claim 1, wherein the proportion of the organic and/or inorganic acids is in a concentration range form 0 to 80% by weight, based on the total amount of the medium, where the added acids each have a pKa value between 0 and 5. 12. A printable etching medium as claimed in claim 1, comprising a solvent that is: water, a mono- or polyhydric alcohols alcohol, such as glycerol, 1,2-propanediol, 1,4- butanediol, 1,3-butanediol, 1,5-pentanediol, 2-ethyl-1-hexenol, ethylene glycol, diethylene glycol, dipropylene glycol, or an ester thereof, ethylene glycol monobutyl ether, triethylene glycol monomethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, [2,2-butoxy(ethoxy)] ethyl acetate, an ester of carbonic acid, propylene carbonate, a ketone acetophenone, methyl-2-hexanone, 2- octanone, 4-hydroxy-4-methyl-2-pentanone, l-methyl-2-pyrrolidone, or a mixture thereof, in an amount of 10 to 90% by weight based on the total amount of the medium. 13. A printable etching medium according to claim 1, comprising a polymer particle that is a polystyrene, polyacrylic, polyamide, polyimide, polymethacrylate, melamine, urethane, benzoguanine or a phenolic resin, a silicone resin, a micronised cellulose, a fluorinated polymer (PTFE, PVDF) or a micronised wax. 14. A printable etching medium as claimed in claim 1, wherein said inorganic particle is an aluminium oxide, a calcium fluoride, a boron oxide or a sodium chloride. 15. A printable etching medium as claimed in claim 1, comprising one or more homogeneously dissolved thickener that is a cellulose, a cellulose derivative, a starch, a starch derivative, xanthan or a polyvinylpyrrolidone polymer based on an acrylate of functionalised vinyl units. 16. A printable etching medium as claimed in claim 1, comprising a homogeneously distributed thickener that is : a) a cellulose/cellulose derivative and/or b) starch/starch derivative and/or c) xanthan and/or d) a polyvinylpyrrolidone polymer based on an acrylate of functionalised vinyl units in an amount of 0.5 to 25% by weight, based on the total amount of the etching medium. 17. A printable etching medium as claimed in claim 1, comprising 0 to 5% by weight, based on the total amount, of additives selected from the group of antifoams, thixotropic agents, flow-control agents, deaerators and adhesion promoters. 18. The etching medium as claimed in claim 1, comprising a viscosity at 20°C. in the range from 10 to 25 Pas at a shear rate of 25s-1. 19. The medium as claimed in claim 1, wherein said optional additive is an antifoam agent, a thixotropic agent, a flow-control agent, a deaerator or an adhesion promoter. 20. The etching medium as claimed in claim 1, comprising a) an etching component b) 2 to 20% by weight, based on the total amount of a solvent c) 20 to 40% by weight, based on the total amount of polymer particles having a relative particle diameter in the range from 1 µm to 10 µm, said medium having a viscosity at 20°C. in the range 10 to 25 Pas at a shear rate of 25 s-1. 21. The etching medium as claimed in claim 1, having a viscosity at 20°C. in the range from 15 to 20 Pas at a shear rate of 25 s-1. 22. A method of etching comprising applying to a surface an etching medium of claim 1 and removing it after a reaction time of 10 s-15 min. 23. An etching process comprising applying-a printable etching medium as claimed in claim 1 to the surface to be etched and removing said printable etching medium after a reaction time of 10 s-15 min. 24. A process as claimed in claim 23, wherein said surface to be etched is a photovoltaic surface, a semiconductor surface, a high-performance electronic surface, a photodiode, a viewing window for a valve or a measuring instrument, a glass support for an outdoor application, a medical glass surface, a decorative glass, a sanitary glass, a cosmetic article, a food or beverage container surface, a flat glass or a flat-panel screen. 25. A process as claimed in claim 23, wherein said medium is applied by an off-contact and on-contact screen, pad, stamp, ink-jet or manual printing process. 26. A process as claimed in claim 23, wherein said surface to be etched is a support for a solar cell or a thermal collector. 27. A process as claimed in claim 23, for the etching of SiO2— or silicon nitride-containing glasses as uniform single-material non-porous and porous solids or of corresponding non- porous or porous glass layers of variable thickness which have been produced on other substrates. 28. A process as claimed in claim 23, for the etching of uniform, single-material, non- porous or porous glasses based on silicon dioxide or nitride systems and of layers of variable thickness of such systems. 29. A process as claimed in claim 23, for removing silicon oxide/doped silicon oxide and silicon nitride layers, for the selective opening of passivation layers comprising silicon oxide and silicon nitride for the production of dual-stage selective emitters and/or local p+ back- surface fields. 30. A process as claimed in claim 23, for the opening of passivation layers comprising silicon oxide and silicon nitride in the process for the production of semiconductor components and their circuits. 31. A process as claimed in claim 23, for the opening of passivation layers comprising silicon oxide and silicon nitride in the process for the production of components for high performance electronics. 32. A process as claimed in claim 23, for mineralogical, geological and microstructural investigations. 33. An etching process as claimed in claim 23, wherein said etching is carried out at elevated temperatures in the range from 40 to 200°C. and further comprising removing said printable etching medium after a reaction time of 30 s to 2 min. 34. A process for the etching of inorganic, glass-like, crystalline surfaces, comprising applying an etching medium as claimed in claim 1 over the entire surface of specifically, in accordance with the etching structure pattern, only at the points where etching is desired, and, after etching is complete, is rinsed off using a solvent or solvent mixture or burned off by heating. 35. A process as claimed in claim 34, wherein said doping is carried out by heating. 36. A process as claimed in claim 34, wherein said etching medium is rinsed off with water after etching is complete. 37. An etching process as claimed in claim34, wherein said etching is carried out at elevated temperatures in the range from 30 to 330°C. 38. An etching process as claimed in claim 34, wherein said etching of SiO2 or SiNx layers is carried out at elevated temperatures in the range from 50 to 100°C. at etching rates of 0.5 to 8 nm/s. ABSTRACT Title: PRINTABLE MEDIUM FOR THE ETCHING OF SILICON DIOXIDE AND SILICON NITRIDE LAYERS A printable etching medium in the form of a paste for etching and optionally doping inorganic glass-like or crystalline layers selected from the group of glasses based on silicon dioxide and the glasses based on silicon nitride, which are located on crystalline or amorphous silicon surfaces, comprising a) an etching component b) solvent c) polymer particles having a relative particle diameter in the range from 10 nm to 50 µm, d) optionally a homogeneously dissolved organic thick-ener e) optionally at least one inorganic and/or organic acid, f) optionally an additive and g) optionally inorganic particles, said medium having a viscosity at 20° C. in the range from 6 to 35 Pa*s at a shear rate of 25 s-1.

Full Text

Printable medium for the etching of silicon dioxide and
silicon nitride layers
The present invention relates to a novel printable etching medium having
non-Newtonian flow behaviour for the etching of surfaces in the produc-
tion of solar cells, and to the use thereof.
The present invention furthermore also relates to etching and doping
media which are suitable both for the etching of inorganic layers and for
the doping of underlying layers.
In particular, these are corresponding particle-containing compositions by
means of which extremely fine structures can be etched very selectively
without damaging or attacking adjacent areas.
The problem of structuring oxide layers on a support material arises, for
example, in the production of solar cells. A crystalline silica solar cell
usually consists of a p-conducting substrate into which a layer of an n-
conducting substance, for example phosphorus, of uniform thickness is
diffused on the front side. A metallically conducting contact is applied to
the front and reverse sides of the wafer for conduction of the current pro-
duced on incidence of light. With regard to an inexpensive production
process which is suitable for mass production, the contact is usually pro-
duced by screen printing.
Besides the oxide layers that have to be structured during solar cell pro-
duction, silicon nitride layers also have to be etched. For the etching of
corresponding nitride layers, the methods used have to be modified and
the etching pastes adapted in a suitable manner.
1. Prior art and object of the invention
The surfaces of crystalline silicon solar cells are coated with thin inorga-
nic layers during the production process, and optionally also after the end
thereof. These layers have thicknesses in the range from 20 to 200 nm,
in most cases in the range from 50 to 150 nm.

Duririg the process for the production of crystalline silica solar cells, it is
therefore advantageous in a number of process steps to etch fine lines
into these inorganic layers of the solar cell;
These openings in the surface of the solar cell can be used, for example,
for the production of a so-called selective emitter, also known as 2-stage
emitter. To this end, a high degree of n-doping, preferably by means of
phosphorus diffusing in, is produced in a subsequent diffusion step in the
partial openings of a diffusion barrier located on the silicon.
In the present description, inorganic surfaces is taken to mean oxidic and
nitride-containing compounds of silicon, in particular silicon oxide and
silicon nitride surfaces. The mode of action of such diffusion barriers is
known to the person skilled in the art and is described in the literature
[A. Goetzberger; B. VoB; J. Knobloch, Sonnenenergie: Photovoltaik
[Solar Energy: Photovoltaics], Teubner Studienbucher Stuttgart 1997,
pp 40; 107]. These diffusion barriers can be produced in a variety of
ways:
Very dense silicon dioxide layers are obtained, for example, by heat
treatment of silicon in an oxygen-containing atmosphere at temperatures
in the region of 900°C (thermal oxide).
Also known to the person skilled in the art is the deposition of silicon di-
oxide by the CVD process. Depending on the way the reaction is carried
out, a distinction is made here between, inter alia, the following proc-
esses:
- APCVD (atmospheric pressure CVD)
- PE-CVD (plasma enhanced CVD)
- LP-CVD (low pressure CVD)
A common feature of these processes is that the desired inorganic com-
pound is obtained from the gas phase of a volatile precursor, for example
silane (SiH4) or TEOS (tetraethyl orthosilicate) in the case of silicon di-
oxide, by deposition of the precursor on the target substrate with decom-
position.

Silicon dioxide layers which form a diffusion barrier can also be obtained
by means of wet-chemical coating with a liquid or dissolved solid precur-
sor in a solvent or solvent mixture. These liquid systems are usually ap-
plied to the substrate to be coated by spin coating. These systems are
known to the person skilled in the art as spin-on-glass (SOG).
In many cases, the SiO2 layer applied also remains as reflection-reducing
passivation layer. This is particularly frequently the case for thermally
grown SiO2.
Silicon nitride layers are used less as diffusion barriers in the art of crys-
talline solar cells, although they are in principle likewise suitable for this
purpose. Silicon nitride layers are mainly used as passivation and anti-
reflection layers.
It is also advantageous in the production of crystalline silicon solar cells
to be able to produce openings in a targeted manner in the silicon nitride
layers. An example which may be mentioned here is the application of
electrically conductive pastes. These metal pastes are usually "fired
through" the silicon nitride layer at temperatures in the region of 600°C,
facilitating an electrical contact to the emitter layer. Due to the high tem-
peratures, polymer-based (epoxy or phenolic resin) metallisation pastes
cannot be used. Crystal defects and metallic contamination in the under-
lying silicon also arise in the "fire-through process". Due to the system,
the passivation layer is additionally completely destroyed by the overlying
printed-on metal paste. A partial, narrower opening of the silicon nitride
layer for electrical contacting would be more advantageous, with
retention of the passivation layer in the edge regions, which are covered
by the overlying metallisation layer.
Besides the pure diffusion barriers consisting of silicon dioxide or silicon
nitride, it is also possible to use thin glass layers in the production of
crystalline silicon solar cells.
Definition of glass:
Glass is taken to mean per se a homogeneous material, for example
quartz, window glass, borosilicate glass, and also thin layers of these

materials produced on other substrates (for example ceramics, metal
sheets, silicon wafers) by various processes known to the person skilled
in the art (CVD, PVD, spin-on, thermal oxidation, inter alia).
Glasses below is taken to mean silicon oxide- and silicon nitride-con-
taining materials which are in the solid amorphous physical state without
crystallisation of the glass components and which have a high degree of
structural disorder in the microstructure owing to the lack of long-range
order.
Besides pure SiO2 glass (quartz), all glasses (for example doped
glasses, such as borosilicate, phosphosilicate, borophosphosilicate
glasses, coloured, milk and crystal glasses, optical glasses) which con-
tain SiO2 and other components, in particular elements such as, for ex-
ample, calcium, sodium, aluminium, lead, lithium, magnesium, barium,
potassium, boron, beryllium, phosphorus, gallium, arsenic, antimony,
lanthanum, zinc, thorium, copper, chromium, manganese, iron, cobalt,
nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, sil-
ver, cerium, caesium, niobium, tantalum, zirconium, neodymium, praseo-
dymium, which occur in the glasses in the form of oxides, carbonates,
nitrates, phosphates, sulfates and/or halides or function as doping ele-
ments in the glasses, are covered. Doped glasses are, for example,
borosilicate, phosphosilicate, borophosphosilicate, coloured, milk, crystal
glasses and optical glasses.
The silicon nitride may likewise comprise other elements, such as boron,
aluminium, gallium, indium, phosphorus, arsenic or antimony.
Definition of silicon oxide- and silicon nitride-based systems:
Silicon oxide-based systems are defined below as all crystalline systems
which do not fall under the definition of amorphous SiO2 glasses given
above and are based on silicon dioxide; these can be, in particular, the
salts and esters of orthosilicic acid and condensation products thereof-
generally known as silicates by the person skilled in the art - as well as
quartz and glass-ceramics.
Furthermore, other silicon oxide- and silicon nitride-based systems, in
particular the salts and esters of orthosilicic acid and condensation prod-

ucts thereof, are encompassed. Besides pure SiO2 (quartz, tridymite,
cristobalite), all SiO2-based systems built up from SiO2 or "discrete"
and/or linked [SiO4] tetrahedra, such as, for example, mesosilicates,
sorosilicates, cyclosilicates, inosilicates, phyllosilicates, tectosilicates,
and other components, in particular elements/components such as, for
example, calcium, sodium, aluminium, lithium, magnesium, barium,
potassium, beryllium, scandium, manganese, iron, titanium, zirconium,
zinc, cerium, yttrium, oxygen, hydroxyl groups, halides, are also encom-
passed.
Silicon nitride-based systems are defined below as all crystalline and
partially crystalline (usually referred to as microcrystalline) systems which
do not fall under the definition given above for the amorphous silicon
nitride glasses/layers. These include Si3N4 in its α-Si3N4 and β-Si3N4
modifications and all crystalline and partially crystalline SiNx and SiNx:H
layers. Crystalline silicon nitride may comprise other elements, such as
boron, aluminium, gallium, indium, phosphorus, arsenic and antimony.
Etching of structures
The use of etchants, i.e. chemically aggressive compounds, results in the
dissolution of the material exposed to the etchant attack. In most cases,
the aim is completely to remove the layer to be etched. The end of the
etching is reached by the encountering of a layer which is substantially
resistant to the etchant. In addition, there is the process known to the
person skilled in the art of partial removal of a layer by etching to a target
thickness which is usually defined.
Etching of structures on silicon oxide- and silicon nitride-based glasses
and other silicon oxide- and silicon nitride-based systems:
According to the current state of the art, any desired structures can be
etched selectively in silicon oxide- and silicon nitride-based glasses and
other silicon oxide- and silicon nitride-based systems or surfaces thereof
and layers thereof of variable thickness directly by laser-supported etch-
ing methods or, after masking, by wet-chemical methods ([1] D.J. Monk,
D.S. Soane, R.T. Howe, Thin Solid Films 232 (1993), 1; [2]J. Buhler, F.-

P. Steiner, H. Baltes, J. Micromech. Microeng. 7 (1997), R1) or by dry-
etching methods ([3] M. Kohier "Atzverfahren fur die Mikrotechnik" [Etch-
ing Methods for Microtechnofogy], Wiley VCH 1983).
In the laser-supported etching methods, the laser beam scans the entire
etching pattern on the glass dot by dot or line by line in the case of vec-
tor-orienting systems, which, besides a high degree of precision, also
requires considerable adjustment effort and time.
The wet-chemical and dry-etching methods include material-intensive,
time-consuming and expensive process steps.
A. Masking of the areas not to be etched, for example by:
» Photolithography: Production of a negative or positive of the etching
structure (depending on the resist), coating of the substrate surface
(for example by spin-coating with a liquid photoresist), drying of the
photoresist, exposure of the coated substrate surface, development,
rinsing, optionally drying
B. Etching of the structures by:
• dip methods (for example wet etching in wet-chemistry benches): dip-
ping of the substrates into the etching bath, etching operation, re-
peated rinsing in H2O cascade sinks, drying
• spin-on or spray methods: the etching solution is applied to a rotating
substrate, the etching operation can be carried out without/with input of
energy (for example IR or UV irradiation), this is followed by rinsing
and drying
• dry-etching methods, such as, for example, plasma etching, in expen-
sive vacuum units or etching with reactive gases in flow reactors

C. Removal of the photoresist:
in the final process step, the photoresist covering the protecting areas of
the substrate must be removed. This can be carried out by means of sol-
vents, such as, for example, acetone, or dilute aqueous alkaline solu-
tions. The substrates are finely rinsed and dried.
Full-area etching of silicon oxide- and silicon nitride-based glasses and
other silicon oxide- and silicon nitride-based systems:
In order to etch silicon oxide- and silicon nitride-based glasses and other
silicon oxide- and silicon nitride-based systems and layers of variable
thickness thereof over the entire area completely or only to a certain
depth, use is predominantly made of wet-etching methods. The silicon
oxide- and silicon nitride-based glasses and other silicon oxide- and sili-
con nitride-based systems and layers of variable thickness thereof are
dipped into etching baths, which usually contain the toxic and highly
caustic hydrofluoric acid and optionally additives of other mineral acids.
The disadvantages of the etching methods described lie in the time-con-
suming, material-intensive and expensive process steps which are in
some cases complex in technological and safety terms and are frequently
carried out discontinuously.
International Application WO 01/83391 A describes etching media in the
form of printable, homogeneous, particle-free etching pastes having non-
Newtonian flow behaviour for the etching of inorganic, glass-like amor-
phous or crystalline surfaces, in particular of glasses or ceramics, pref-
erably SiO2- or silicon nitride-based systems, and the use of these etch-
ing media. In particular on printing of surfaces, use of these particle-free
media gave rise to problems due to inadequate resilience of the printed
lines, dots or structures (inadequate structure fidelity), meaning that a
significant broadening of the originally printed lines occurs (bleeding of
the etching species on the substrate).
US 5,688,366 A uses particle-containing etching pastes for the etching of
a transparent conductive layer (for example ITO). The etching pastes

used are prepared from molten iron chloride containing water of crystalli-
sation, glycerol and polymer particles. These compositions are suitable
for the etching of lines having a width of about 1 mm. Experiments have
shown that these etching pastes are not suitable for the etching of very
thin lines having a width of less than 1 mm cleanly and without flaws, ir-
respective of whether polymer particles having a diameter of 0.01 µm or
of 30 µm are employed for the preparation of the pastes.
Objective
The object of the present invention is therefore to provide novel, inexpen-
sive etching pastes for the etching of very uniform, thin lines having a
width of less than 100 µm, in particular of less than 80 µm, and of micro-
fine structures on silicon dioxide and/or silicon nitride layers which are lo-
cated on silicon solar cells. A further object of the present invention is to
provide novel etching media which can be removed from the treated sur-
faces after the etching under the action of heat in a simple manner with-
out leaving residues.
2. Description of the invention
More recent experiments have now shown that, in contrast to previous
experience, the printing properties of etching pastes can advantageously
be improved if suitable, selected polymer particles are added. In this con-
nection, polymer particles which form a network in the prepared pastes
through physical interaction and/or chemical reaction with the other con-
stituents of the medium, simultaneously causing an increase in the visco-
sity of the composition, have proven particularly suitable. Entirely unex-
pectedly, the added particles also contribute to an improvement in the
printability of the medium.
Given a suitable choice of the added particulate components, it may even
be possible to omit entirely the addition of a thickener, which is usually
homogeneously distributed in known particle-free pastes.

The object of the present application is therefore achieved by the provi-
sion of a novel printable etching medium having non-Newtonian flow be-
haviour in the form of an etching paste for the etching of inorganic, glass-
like or crystalline surfaces selected from the group of glasses based on
silicon oxide and glasses based on silicon nitride,
which comprises polymer particles consisting of a material selected from
the group of polystyrene, polyacryl, polyamide, polyimide, polymeth-
acrylate, melamine, urethane, benzoguanine, phenolic resin, silicone
resin, fluorinated polymers (PTFE, PVDF, inter alia) and micronised wax,
in the presence of an etching component, solvent, thickener, optionally at
least one inorganic and/or organic acid, and optionally additives, such as
antifoams, thixotropic agents, flow-control agents, deaerators, adhesion
promoters. The etching medium according to the invention is effective
even at temperatures of 15 to 50°C or can optionally be activated by in-
put of energy. Preferred forms of the pastes according to the invention
and use thereof arise from Claims 2-18. The present invention further-
more relates to a process for the etching and optionally for the simulta-
neous doping of inorganic, glass-like, crystalline surfaces according to
Claims 29 and 33. Claim 28 relates to particular embodiments of the use
of the etching pastes according to the invention.
3. Detailed description of the invention
In accordance with the invention, the novel etching pastes having thixo-
tropic, non-Newtonian properties are used to structure silicon dioxide or
nitride layers in a suitable manner during the process for the production
of products for photovoltaics, semiconductor technology, high-perform-
ance electronics, of solar cells or photodiodes. To this end, the paste is
printed in a single process step onto the surface to be etched and re-
moved again after a pre-specified reaction time. In this way, the surface
is etched and structured in the printed areas, while unprinted areas re-
main in the original state.
The surface to be etched here can be a surface or part-surface of silicon
oxide- or silicon nitride-based glass and other silicon oxide- and silicon
nitride-based systems, and/or a surface or part-surface of a porous and

1 >
non-porous layer of glass and other silicon oxide- and silicon nitride-
based systems on a support material.
A suitable process having a high degree of automation and having high
throughput utilises printing technology for the transfer of the etching
paste to the substrate surface to be etched. In particular, the screen, pad,
stamp, ink-jet printing processes are printing processes that are known to
the person skilled in the art. Manual application is likewise possible.
Depending on the screen, plate or stamp design or cartridge addressing,
it is possible to apply the printable, homogeneous, particle-free etching
pastes having non-Newtonian flow behaviour which are described in ac-
cordance with the invention over the entire area or selectively in accor-
dance with the etch structure pattern only in the areas where etching is
desired. All masking and lithography steps which are otherwise neces-
sary are thus superfluous. The etching operation can be carried out with
or without energy input, for example in the form of heat radiation (using
IR lamps).
The actual etching process is subsequently completed by washing the
surfaces with water and/or a suitable solvent. More precisely, the print-
able, polymer particle-containing etching pastes having non-Newtonian
flow behaviour are rinsed off the etched areas using a suitable solvent
after etching is complete.
Use of the etching pastes according to the invention thus enables long
runs to be etched inexpensively on an industrial scale in a suitable,
automated process.
In a preferred embodiment, the etching paste according to the invention
has a viscosity in the range from 10 to 500 Pas, preferably from 50 to
200 Pas. The viscosity is the material-dependent component of the fac-
tional resistance which counters movement when adjacent liquid layers
are displaced. According to Newton, the shear resistance in a liquid layer
between two sliding surfaces arranged parallel and moved relative to one
another is proportional to the velocity or shear gradient G. The propor-
tionality factor is a material constant which is known as the dynamic vis-
cosity and has the dimension m Pa.s. In Newtonian liquids, the propor-

tionality factor is pressure- and temperature-dependent. The degree of
dependence here is determined by the materia! composition. Liquids or
substances having an in homogeneous composition have non-Newtonian
properties. The viscosity of these substances is additionally dependent
on the shear gradient.
For the etching of fine structures, having line widths of printed etching media,it has now been found to be particularly advanta-
geous to thicken etching media completely or partially using finely divided
particulate systems instead of particle-free etching pastes comprising a
homogeneously distributed polymer (types see WO 01/83391 A) for
thickening. Particularly suitable for this purpose are polymer particles
which interact with the other components of the composition and form a
network by means of chemical bonds or a purely physical interaction at
the molecular level. The relative particle diameters of these systems can
be in the range from 10 nm to 30 urn. Corresponding polymer particles
having a relative particle diameter in the range from 1 to 10 µm have
proved particularly advantageous. Particles which are particularly suitable
for the purpose according to the invention can consist of the following
materials:
- polystyrene
- polyacryl
- polyamide
- polyethylene
- ethylene-vinyl acetate copolymer
- ethylene-acrylic acid-acrylate terpolymer
- ethylene-acrylate-maleic anhydride terpolymer
- polypropylene
- polyimide
- polymethacrylate
- melamine, urethane, benzoguanine, phenolic resin
- silicone resin
- fluorinated polymers (PTFE, PVDF), and
- micronised waxes

The use of a very finely divided polyethylene powder, which is, for exam-
ple, currently marketed by DuPont PolymerPowders Switzerland under
the trade name COATHYLENE HX® 1681, having relative particle dia-
meters d50 value of 10 µm, has proven particularly suitable in the experi-
ments.
These particulate thickeners can be added to the etching medium in
amounts of 1 to 50% by weight, advantageously in the range from 10 to
50% by weight, in particular from 25 to 35% by weight.
Also suitable in principle are particulate polymeric thickeners based on
- polystyrene
- polyacryl
- polyamide
- polyimide
- polymethacrylate
- melamine, urethane, benzoguanine, phenolic resin
- silicone resin.
Compared with the particle-free etching pastes described in
WO 01/83391 A, the addition of the particulate thickeners according to
the invention has enabled the following improvements to be achieved:
I. Particulate thickening results in improved resilience of the etching
medium. The particles form a skeleton-structure in the etching me-
dium. Similar structures are known to the person skilled in the art
from highly dispersed silicic acid (for example Aerosil®). In particular
in screen printing of the etching pastes, a broadening of the printed
structures due to flow can be substantially prevented or at least
greatly restricted by the present invention. The printed, and thus
paste-covered area therefore corresponds substantially to the area
specified in the screen layout. Many inorganic particles, such as, for
example, silicic acid or modified silicic acid, cannot be employed for
thickening the etching medium owing to their reactivity with the etch-
ing component employed. For example, a chemical reaction of silicic
acid with NH4HF2 takes place if the latter serves as etching compo-
nent.

II. With the aid of particulate thickening, lines of greater print height with
retained width are, in addition, printed on use of the same screen or
mask than on use of corresponding particle-free pastes, as de-
scribed, for example, in WO 01/83391 A. This simultaneously results
in a greater application rate of etching component per unit area. If
relatively thick silicon dioxide or silicon nitride layers (> 100 nm) are
to be etched, this is a particular advantage for complete etching.
III. The more pronounced non-Newtonian or thixotropic properties of the
etching paste have a particularly advantageous effect for screen
printing and result in considerably improved results. In particular, this
is evident in a shortened etching time or an increased etching rate for
the same etching time and especially in a greater etching depth in the case of relatively thick layers.
IV. The thickening associated with the addition of polymer particles ac-
cording to the invention results in a considerably lower binding capa-
city of the etching paste. Given a specific choice of the particles
added, an increased etching rate and thus a considerably increased
etching depth are, surprisingly, achieved for the same amount of
added etching component.
V. The significantly greater print height achieved under the same
printing conditions, i.e. on use of the same screen and the same
printing parameters, furthermore causes significantly delayed drying
of the printed etching species. This enables the etching species to act
on the substrate for longer. It is particularly important in the case of
accelerated etching under elevated temperatures. In addition, the
material remaining after the etching process can be removed
significantly more easily in the final cleaning process.
Significant improvements in the present compositions arise; in particular,
through a considerably improved screen-printing behaviour, enabling
continuous printing of surfaces to be treated without interruptions.The
use of the etching pastes according to the invention enables considerably
finer etching structures since the pastes have greater viscosities on addi-
tion of the same amounts of thickener in the presence of polymer parti-

cles. This enables the pastes to be applied in printing with a higher paste layer and consequently for the layers to be etched deeper. The improved
rinsing behaviour (wafer cleaning) after etching also shortens the time
required for subsequent cleaning.
Surprisingly, experiments have shown that the addition of corresponding
fine polymer particles also has an advantageous effect in processes for
the selective etching of inorganic surfaces for the production of selective
emitter structures in solar cells, in which, besides etching, specific phos-
phorus doping for the production of n++ regions is also desired. Corre-
sponding etching and doping pastes are described, for example, in WO
03/034504 A1. In contrast to the pure etching pastes, these pastes, after
application to the wafer surfaces to be etched, are heated over the entire
surface or locally depending on the particles present in the paste to tem-
peratures in the range from 250 to 350°C for from 30 to 120 seconds and
optionally, for additional n++ doping, to temperatures >800°C, in particular
to temperatures in the range from 800 to 1050°C, for 20 - 40 minutes.
The selected temperature is of course set in such a way that changes in
the particles present in the paste do not give rise to any disadvantages.
Corresponding etching media may comprise the various forms of phos-
phoric acid or suitable phosphoric acid salts or compounds, which are
decomposed to the corresponding phosphoric acid on heating, as etching
and as doping components.
It has been found that orthophosphoric acid, metaphosphoric acid, pyro-
phosphoric acid and salts thereof and here in particular the ammonium
salts ((NH4)2HPO4, NH4H2PO4, (NH4)3PO4) and other compounds which
form one of these compounds on thermal decomposition are capable of
completely etching away silicon nitride layers having a layer thickness of
70 mm within a few seconds to minutes at temperatures above 250°C. At
300°C, the etching time is about 60 seconds.
For the preparation of the particle-containing media according to the in-
vention, the solvents, etching components, thickeners, particles and ad-
ditives are mixed successively with one another and stirred for a suffi-
cient time until a viscous paste having thixotropic properties has formed.

The stirring can-be carried put with warming to a suitable temperature. The, components are usually stirred with one another at room tempera-
ture.
Preferred uses of the printable etching pastes according to the invention
arise for the described processes for the structuring of oxide layers ap-
plied to a support material, for the production of solar cells having a se-
lective emitter layer on the light incidence side and for the production of
solar cells having a selective emitter layer on the light incidence side and
a back-surface field on the back.
For application of the pastes to the areas to be treated, the etching
pastes can be printed through a fine-mesh screen which contains the
print template (or etched metal screen). In a further step, the pastes can
be baked in the screen-printing process by the thick-layer method
(screen printing of conductive metal pastes), enabling the electrical and
mechanical properties to be fixed. On use of the etching pastes
according to the invention, the baking (firing through the dielectric layers)
can instead also be omitted and the applied etching pastes washed off
with a suitable solvent or solvent mixture after a certain reaction time.
The etching action is terminated by the washing-off.
Particularly suitable printing methods are essentially screen printing with
screen separation or stencil printing without separation. In screen print-
ing, the separation a of a screen is usually several hundred µm with a tilt
angle a between the edge of the squeegee, which pushes the etching
printing paste over the screen, and the screen. The screen is held by a
screen frame, while the squeegee is passed over the screen at a squee-
gee velocity v and a squeegee pressure P. In the process, the etching
paste is pushed over the screen. During this operation, the screen comes
into contact with the substrate in the form of a line over the squeegee
width. The contact between screen and substrate transfers the vast ma-
jority of the screen printing paste located in the free screen meshes onto
the substrate. In the areas covered by the screen meshes, no screen
printing paste is transferred onto the substrate. This enables screen print-
ing paste to be transferred in a targeted manner to certain areas of the
substrate.

After the end of the movement E, the squeegee is raised off the screen. The screen is tensioned uniformly using a screen stretcher with hydrau-
lic/pneumatic tension and clamping device. The screen tension is moni-
tored by defined sag of the screen in a certain area at a certain weight
using a dial gauge. With specific pneumatic/hydraulic printing machines,
the squeegee pressure (P), the printing velocity (V), the off-contact dis-
tance (A) and the squeegee path (horizontal and vertical, squeegee an-
gle) can be set with various degrees of automation of the working steps
for trial and production runs.
Printing screens used here usually consist of plastic or steel-wire cloth. It
is possible for the person skilled in the art to select cloths having different
wire diameters and mesh widths, depending on the desired layer thick-
ness and line width. These cloths are structured directly or indirectly us-
ing photosensitive materials (emulsion layer). For the printing of extreme-
ly fine lines and in the case of requisite high precision of successive
prints, it may be advantageous to use metal stencils, which are likewise
provided directly or indirectly with a hole structure or line structure.
In order to carry out the etching, an etching paste, as described, for ex-
ample, in Example 1, is prepared. Using an etching paste of this type, a
thermal SiO2 having a thickness of approx. 100 nm can be removed se-
lectively within 60 seconds at 50°C after screen printing. The etching is
subsequently terminated by dipping the Si wafer into water and then
rinsing with the aid of a fine water spray.
For the production of solar cells, wafers comprising p-doped Pz silicon
having orientation, for example, are selected. In these, a short,
basic etching enables a structure to be produced on the surface which
improves the light incidence geometry for reducing reflections. A thin
dopant coating film comprising a boron-containing compound can be
spin-coated onto the back and dried. The wafers prepared in this way are
placed in a tray and introduced into an oven pre-heated to 1000 to
1100°C. An oxygen atmosphere is established in the oven, so that an
oxide layer forms directly on all wafer surfaces that are not covered by
the boron dopant coating film. At the same time, boron is expelled from
the dopant coating film and diffuses into the back of the wafers. p+-doped

regions with a depth of approx. 1 to 5 µm form. This embodiment of a
solar cell is known to the person skilled in the art under the term "back-
surface field". The oxide layers formed on the front can now be structured
using the etching pastes described above.
For example, these oxide layers can be formed as masks for high n+-
phosphorus dopings for the formation of selective emitter layers, while
significantly less n+-doping is aimed at in the masked areas.
After opening of the pn junction, which would result in short circuits in the
solar cell, for example by plasma etching or opening using a LASER
beam, the electrical contacts are applied to the front and back of the cell.
This can be carried out by means of two successive screen-printing steps
using a paste, which may, besides the binders and oxidic additives, com-
prise conductive silver particles and/or aluminium. After the printing, the
printed contacts are baked at about 700 to 800°C.
The present description enables the person skilled in the art to use the
invention comprehensively. If anything is unclear, it goes without saying
that the cited publications and patent literature should be used. Corre-
spondingly, these documents are regarded as part of the disclosure con-
tent of the present description.
4. Examples
For better understanding and in order to illustrate the invention, ex-
amples are given below which are within the scope of protection of
the present invention. These examples also serve to illustrate pos-
sible variants. Owing to the general validity of the inventive principle
described, however, the examples are not suitable for reducing the
scope of protection of the present application to these alone.
The temperatures given in the examples are always in °C. It further-
more goes without saying that the added amounts of the components
in the composition always add up to a total of 100% both in the
description and in the examples.

Example 1 ,
Etching paste consisting of homogeneous and particulate thickeners
To a solvent mixture consisting of
15 g of ethylene glycol monobutyl ether
15 g of triethylene glycol monomethyl ether
29 g of polycarbonate
are added successively with stirring
72 g of formic acid (100%) and
46 g of ammonium hydrogen difluoride solution 35%.
Then
46 g of polyvinylpyrrolidone (PVP) K-120
are slowly added in portions to the solution with vigorous stirring, and the
mixture is stirred for a further 30 minutes. The clear paste pre-thickened
with a homogeneous thickener (PVP) is then mixed with
60 g of Vestosint 2070
and the mixture is stirred for a further 2 hours.
The paste, which is now ready to use, can be printed using a 280 mesh
stainless-steel cloth screen. In principle, polyester or similar screen ma-
terials can also be used.
Example 2
Etching paste consisting of a particulate thickener
to a solvent mixture consisting of
15 g of ethylene glycol monobutyl ether
15 g of triethylene glycol monomethyl ether
29 g of polycarbonate
are added successively with stirring
72 g of formic acid (100%) and
46 g of ammonium hydrogen difluoride solution 35%.
The clear homogeneous mixture is then mixed with
100g of Vestosint 2070,
and the mixture is stirred for a further 2 hours.

The paste, which is now ready to use, can be printed using a 280 mesh stainless-steel cloth screen. In principle, polyester or similar screen ma-
terials can also be used.
The etching paste prepared has proven to be stable on storage over a
long time with retention of the advantageous etching properties.
Further examples of compositions according to the invention having ad-
vantageous properties are given in the following tables:

Further examples of compositions according to the invention having ad- vantageous properties for the etching of SiNx are given in the following
tables.

Comparative Example: Etching paste without particulate additives
For a comparative test, the following pressure and etching parameters
were used:
Screen: steel screen having a mesh count of
280 mesh/inch and a filament diameter of
25 µm and an emulsion thickness of 15 urn.
Layout: 100 µm lines
Screen printing machine: EKRA E1
Wafers: single-crystal silicon wafers, with 100 nm
thermal SiO2
Etching: heated at 50°C for 30 s
Result: Line width after etching and rinsing: about 180 µm on average
Comparative Example: Etching paste with particulate additives
For a comparative test, the following pressure and etching parameters
were used:
Screen: steel screen having a mesh count of
280 mesh/inch and a filament diameter of
25 µm and an emulsion thickness of 15 urn.
Layout: 100 pm lines
Screen printing machine: EKRA E1
Wafers: single-crystal silicon wafers, with 100 nm
thermal SiO2
Etching: heated at 50°C for 30 s
Result: The etched line had a width of 105 µm on average.

We Claim:
1. A printable etching medium in the form of a paste for etching and optionally doping
inorganic glass-like or crystalline layers selected from the group of glasses based on
silicon dioxide and the glasses based on silicon nitride, which are located on crystalline or
amorphous silicon surfaces, comprising
a) an etching component
b) solvent
c) polymer particles having a relative particle diameter in the range from 10 nm to 50 urn,
d) optionally a homogeneously dissolved organic thick-ener
e) optionally at least one inorganic and/or organic acid,
f) optionally an additive
and
g) optionally inorganic particles,
said medium having a viscosity at 20° C. in the range from 6 to 35 Pa*s at a shear rate of 25 s-1.
2. A printable etching medium as claimed in claim 1, wherein the polymer particles have a relative
particle diameter in the range from 100 nm to 30 µm.
3. A printable etching medium as claimed in claim 1, comprising polymer particles in an
amount of 1 to 80% by weight, based on the total amount of medium.

4. A printable etching medium as claimed in claim 1, comprising polymer particles in an
amount of 10 to 50% by weight based on the total amount of medium.
5. A printable etching medium as claimed in claim 1, wherein the etching component is
present in an amount of 12 to 30% by weight based on the total amount of medium.
6. A printable etching medium as claimed in claim 1, wherein the thickener is present in an
amount of 3 to 20% by weight, based on the total amount of medium.
7. A printable etching medium as claimed in claim 1, comprising one or different forms to
phosphoric acid, phosphoric acid salts or compounds which are decomposed to the
corresponding phosphoric acid on heating and act as etching and as doping components.
8. A printable etching medium as claimed in claim 1 for surfaces of glasses which comprise
elements selected from the group of calcium, sodium, aluminium, lead, lithium,
magnesium, barium, potassium, boron, beryllium, phosphorus, gallium, arsenic,
antimony, lanthanum, scandium, zinc, thorium, copper, chromium, manganese, iron,
cobalt, nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, silver,
cerium, caesium, niobium, tantalum, zirconium, yttrium, neodymium and praseodymium.
9. A printable etching medium as claimed in claim 1, comprising as etching component, at
least one fluorine compound selected from the group of ammonium, alkali metal and

antimony fluorides, ammonium, alkali metal and calcium bifluorides, alkylated
ammonium and potassium tetrafluoroborates and/or optionally at least one inorganic
mineral acid selected from the group of hydrochloric acid, phosphoric acid, sulfuric acid
and nitric acid and/or optionally at least one organic acid, which may contain a straight-
chain or branched alkyl radical having 1-10 C atoms, selected from the group of the
alkylcarboxylic acids, the hydroxycarboxylic acids and the dicarboxylic acids.
10. A printable etching medium as claimed in claim 9, comprising an organic acid selected
from the group of formic acid, acetic acid lactic acid and oxalic acid.
11. A printable etching medium as claimed in claim 1, wherein the proportion of the organic
and/or inorganic acids is in a concentration range form 0 to 80% by weight, based on
the total amount of the medium, where the added acids each have a pKa value between
0 and 5.
12. A printable etching medium as claimed in claim 1, comprising a solvent that is: water, a
mono- or polyhydric alcohols alcohol, such as glycerol, 1,2-propanediol, 1,4-
butanediol, 1,3-butanediol, 1,5-pentanediol, 2-ethyl-1-hexenol, ethylene glycol,
diethylene glycol, dipropylene glycol, or an ester thereof, ethylene glycol monobutyl
ether, triethylene glycol monomethyl ether, diethylene glycol monobutyl ether,
dipropylene glycol monomethyl ether, [2,2-butoxy(ethoxy)] ethyl acetate, an ester of
carbonic acid, propylene carbonate, a ketone acetophenone, methyl-2-hexanone, 2-

octanone, 4-hydroxy-4-methyl-2-pentanone, l-methyl-2-pyrrolidone, or a mixture
thereof, in an amount of 10 to 90% by weight based on the total amount of the medium.
13. A printable etching medium according to claim 1, comprising a polymer particle that is
a polystyrene, polyacrylic, polyamide, polyimide, polymethacrylate, melamine,
urethane, benzoguanine or a phenolic resin, a silicone resin, a micronised cellulose, a
fluorinated polymer (PTFE, PVDF) or a micronised wax.
14. A printable etching medium as claimed in claim 1, wherein said inorganic particle is an
aluminium oxide, a calcium fluoride, a boron oxide or a sodium chloride.
15. A printable etching medium as claimed in claim 1, comprising one or more
homogeneously dissolved thickener that is a cellulose, a cellulose derivative, a starch, a
starch derivative, xanthan or a polyvinylpyrrolidone polymer based on an acrylate of
functionalised vinyl units.
16. A printable etching medium as claimed in claim 1, comprising a homogeneously
distributed thickener that is :

a) a cellulose/cellulose derivative and/or
b) starch/starch derivative and/or
c) xanthan and/or

d) a polyvinylpyrrolidone polymer based on an acrylate of functionalised vinyl units
in an amount of 0.5 to 25% by weight, based on the total amount of the etching
medium.
17. A printable etching medium as claimed in claim 1, comprising 0 to 5% by weight,
based on the total amount, of additives selected from the group of antifoams, thixotropic
agents, flow-control agents, deaerators and adhesion promoters.
18. The etching medium as claimed in claim 1, comprising a viscosity at 20°C. in the range
from 10 to 25 Pa*s at a shear rate of 25s-1.
19. The medium as claimed in claim 1, wherein said optional additive is an antifoam agent,
a thixotropic agent, a flow-control agent, a deaerator or an adhesion promoter.
20. The etching medium as claimed in claim 1, comprising

a) an etching component
b) 2 to 20% by weight, based on the total amount of a solvent
c) 20 to 40% by weight, based on the total amount of polymer particles having a relative
particle diameter in the range from 1 µm to 10 µm, said medium having a viscosity at 20°C.
in the range 10 to 25 Pa*s at a shear rate of 25 s-1.
21. The etching medium as claimed in claim 1, having a viscosity at 20°C. in the range
from 15 to 20 Pa*s at a shear rate of 25 s-1.

22. A method of etching comprising applying to a surface an etching medium of claim 1
and removing it after a reaction time of 10 s-15 min.
23. An etching process comprising applying-a printable etching medium as claimed in
claim 1 to the surface to be etched and removing said printable etching medium after a
reaction time of 10 s-15 min.
24. A process as claimed in claim 23, wherein said surface to be etched is a photovoltaic
surface, a semiconductor surface, a high-performance electronic surface, a photodiode, a
viewing window for a valve or a measuring instrument, a glass support for an outdoor
application, a medical glass surface, a decorative glass, a sanitary glass, a cosmetic article, a
food or beverage container surface, a flat glass or a flat-panel screen.
25. A process as claimed in claim 23, wherein said medium is applied by an off-contact and
on-contact screen, pad, stamp, ink-jet or manual printing process.
26. A process as claimed in claim 23, wherein said surface to be etched is a support for a
solar cell or a thermal collector.
27. A process as claimed in claim 23, for the etching of SiO2— or silicon nitride-containing
glasses as uniform single-material non-porous and porous solids or of corresponding non-
porous or porous glass layers of variable thickness which have been produced on other
substrates.

28. A process as claimed in claim 23, for the etching of uniform, single-material, non-
porous or porous glasses based on silicon dioxide or nitride systems and of layers of variable
thickness of such systems.
29. A process as claimed in claim 23, for removing silicon oxide/doped silicon oxide and
silicon nitride layers, for the selective opening of passivation layers comprising silicon oxide
and silicon nitride for the production of dual-stage selective emitters and/or local p+ back-
surface fields.
30. A process as claimed in claim 23, for the opening of passivation layers comprising
silicon oxide and silicon nitride in the process for the production of semiconductor
components and their circuits.
31. A process as claimed in claim 23, for the opening of passivation layers comprising
silicon oxide and silicon nitride in the process for the production of components for high
performance electronics.
32. A process as claimed in claim 23, for mineralogical, geological and microstructural
investigations.
33. An etching process as claimed in claim 23, wherein said etching is carried out at
elevated temperatures in the range from 40 to 200°C. and further comprising removing said
printable etching medium after a reaction time of 30 s to 2 min.

34. A process for the etching of inorganic, glass-like, crystalline surfaces, comprising
applying an etching medium as claimed in claim 1 over the entire surface of specifically, in
accordance with the etching structure pattern, only at the points where etching is desired,
and, after etching is complete, is rinsed off using a solvent or solvent mixture or burned off
by heating.
35. A process as claimed in claim 34, wherein said doping is carried out by heating.
36. A process as claimed in claim 34, wherein said etching medium is rinsed off with water
after etching is complete.
37. An etching process as claimed in claim34, wherein said etching is carried out at elevated
temperatures in the range from 30 to 330°C.
38. An etching process as claimed in claim 34, wherein said etching of SiO2 or SiNx layers
is carried out at elevated temperatures in the range from 50 to 100°C. at etching rates of 0.5
to 8 nm/s.

ABSTRACT

Title: PRINTABLE MEDIUM FOR THE ETCHING OF SILICON DIOXIDE AND
SILICON NITRIDE LAYERS
A printable etching medium in the form of a paste for etching and optionally doping
inorganic glass-like or crystalline layers selected from the group of glasses based on silicon
dioxide and the glasses based on silicon nitride, which are located on crystalline or amorphous
silicon surfaces, comprising
a) an etching component
b) solvent
c) polymer particles having a relative particle diameter in the range from 10 nm to 50 µm,
d) optionally a homogeneously dissolved organic thick-ener
e) optionally at least one inorganic and/or organic acid,
f) optionally an additive
and
g) optionally inorganic particles,
said medium having a viscosity at 20° C. in the range from 6 to 35 Pa*s at a shear rate of 25 s-1.

Documents:

02828-kolnp-2007-abstract.pdf

02828-kolnp-2007-claims 1.0.pdf

02828-kolnp-2007-claims 1.1.pdf

02828-kolnp-2007-correspondence others.pdf

02828-kolnp-2007-description complete.pdf

02828-kolnp-2007-form 1.pdf

02828-kolnp-2007-form 2.pdf

02828-kolnp-2007-form 3.pdf

02828-kolnp-2007-form 5.pdf

02828-kolnp-2007-gpa.pdf

02828-kolnp-2007-international publication.pdf

02828-kolnp-2007-international search report.pdf

02828-kolnp-2007-others.pdf

02828-kolnp-2007-pct request form.pdf

02828-kolnp-2007-priority document.pdf

2828-KOLNP-2007-(05-09-2012)-CORRESPONDENCE.pdf

2828-KOLNP-2007-(05-09-2012)-FORM-13.pdf

2828-KOLNP-2007-(05-09-2012)-PETITION UNDER RULE 137.pdf

2828-KOLNP-2007-(23-07-2012)-ABSTRACT.pdf

2828-KOLNP-2007-(23-07-2012)-AMANDED CLAIMS.pdf

2828-KOLNP-2007-(23-07-2012)-ANNEXURE TO FORM 3.pdf

2828-KOLNP-2007-(23-07-2012)-DESCRIPTION (COMPLETE).pdf

2828-KOLNP-2007-(23-07-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

2828-KOLNP-2007-(23-07-2012)-FORM-1.pdf

2828-KOLNP-2007-(23-07-2012)-FORM-2.pdf

2828-KOLNP-2007-(23-07-2012)-OTHERS.pdf

2828-KOLNP-2007-CANCELLED PAGES.pdf

2828-KOLNP-2007-CORRESPONDENCE OTHERS 1.1.pdf

2828-KOLNP-2007-CORRESPONDENCE.pdf

2828-KOLNP-2007-EXAMINATION REPORT.pdf

2828-KOLNP-2007-FORM 13.pdf

2828-KOLNP-2007-FORM 18 1.1.pdf

2828-kolnp-2007-form 18.pdf

2828-KOLNP-2007-GPA.pdf

2828-KOLNP-2007-GRANTED-ABSTRACT.pdf

2828-KOLNP-2007-GRANTED-CLAIMS.pdf

2828-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

2828-KOLNP-2007-GRANTED-FORM 1.pdf

2828-KOLNP-2007-GRANTED-FORM 2.pdf

2828-KOLNP-2007-GRANTED-FORM 3.pdf

2828-KOLNP-2007-GRANTED-FORM 5.pdf

2828-KOLNP-2007-GRANTED-SPECIFICATION-COMPLETE.pdf

2828-KOLNP-2007-INTERNATIONAL PUBLICATION.pdf

2828-KOLNP-2007-OTHERS-1.1.pdf

2828-KOLNP-2007-OTHERS.pdf

2828-KOLNP-2007-PETITION UNDER RULE 137.pdf

2828-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

2828-KOLNP-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

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Patent Number

256248

Indian Patent Application Number

2828/KOLNP/2007

PG Journal Number

21/2013

Publication Date

24-May-2013

Grant Date

22-May-2013

Date of Filing

02-Aug-2007

Name of Patentee

MERCK PATENT GMBH

Applicant Address

FRANKFURTER STRASSE 250, 64293 DARMSTADT

Inventors:

#	Inventor's Name	Inventor's Address
1	STOCKUM, WERNER	WALDSTRASSE 59 64354 REINHEIM
2	KLEIN, SYLKE	AM HUEHNERBUSCH 17 64380 ROSSDORF
3	KUEBELBECK, ARMIN	AUGARTENSTRASSE 45, 64625 BENSHEIM

PCT International Classification Number

C03C 15/00

PCT International Application Number

PCT/EP05/013657

PCT International Filing date

2005-12-19

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102005001343.0	2005-01-11	Germany
2	10200507743.9	2005-02-18	Germany