Title of Invention

ELECTRON BEAM MICRO/NANO FABRICATION METHOD

Abstract

An electron beam microprocessing method is disclosed where in the surface of an AlxGay ln1-x-yAszP1-z (0≤x, y,z≤1) layer (1) containing GaAs as a simple substance and an lnP substrate is irradiated with an electron beam (4) having abritrary electrom beam diameter and current dentisty, so that a natural oxide film (2) formed on the AlxGay ln1-x-yAszP1-z |ayer surface is selectively substituted with or formed into Ga2O3 (3), and then the AlxGay ln1-x-yAszP1-z layer surface is dry-etched using a bromide in single atom layer unit, thereby removing the natural oxide film other than the portion substituted with Ga2O3 and the AlxGay ln1-x-yAszP1-z substrate.

Full Text

DESCRIPTION ELECTRON BEAM MICRO/NANO FABRICATION METHOD Technical Field The present: invention relates to an electron beam micro/nano fabrication method for a compound semiconductor substrate, in particular, the surface of an AlxGay ln1-x-yAszP1-z epitaxially grown on GaAs or an InP substrate. Background Art In recent years, with the improvement in the degree of integration of ULSIs that form the core of microelectronics, circuit patterns in these quantum devices have been increasingly miniaturized. Conventionally, in fabrication processes of semiconductor devices, as basic techniques for removing unnecessary parts of insulating layers and thin metal layers with a high degree of accuracy along resist patterns, various etching methods have been widely employed. As one of these etching methods, dry etching using a halogen gas can be mentioned. This dry etching has been anticipated as being capable of fabricating a structure such as a minute quantum device since etching is carried out in a relatively clean atmosphere in a high vacuum. For example, for Si, which is a representative device material, a dry etching process by a fluorine and chlorine-based halogen gas has been carried out. In addition, there are many reports on a dry etching process with regard to compound semiconductors such as AlxGay ln1-x-yAszP1-z including GaAs as well, however, as a matter of fact, a technical means for enabling fabrication of a quantum element has not been completed. For example, GaAs is a material that is great in mobility compared to Si and is capable of a higher-frequency and higher-speed operation than that of Si, and in place of Si, which has developed on an industrial scale based on advantages such as abundance in resources and crystal integrity, this has been attracting attention for its excellent properties and diversity as one of the component semiconductors to overcome limitations thereof. Moreover, as epitaxial crystal growth techniques for compound semiconductors such as this GaAs, techniques such as an MBE (molecular beam epitaxial growth) method and an MOCVD (metal-organic chemical vapor deposition) method have advanced to allow a high-quality crystal growth, therefore, importance of compound semiconductors as device materials has been increasing. Therefore, as a dry etching method for overcoming technical limitations of a conventional dry etching method using a halogen gas for a compound semiconductor or the like, the present inventor has developed a method for dry-etching the surface of a semiconductor crystal by a bromide in single atomic layer units and has disclosed the same in Japanese Published Unexamined Patent Application No. H08-321483. However, in order to form a circuit pattern on the surface of a GaAs layer with accuracy, it has been necessary to form a dry etching mask even when dry etching is carried out in single atomic layer units as described above. Conventionally, fabrication of this dry etching mask has been carried out by use of an electron beam lithography technique as described in Japanese Published Unexamined Patent Application No. 2001-267213, for example. However, with miniaturization and a greater complexity of circuit patterns of quantum devices in recent years, it has become difficult to fabricate this dry etching mask itself, therefore, a problem has existed in that reproducibility of shape and size has deteriorated, and furthermore, cost considerably has risen. Moreover, since a surface oxide layer such as As2O3, As2O, or Ga2O has been naturally formed on the surface of a GaAs layer, when forming a dry etching mask, it has also been necessary to remove this surface oxide layer. The present invention has been made in view of the problems, and an object thereof is to provide an electron beam micro/nano fabrication method for forming on the spot, on the surface of an AlxGay ln1-x-yAszP1-z including GaAs, a minute circuit pattern having different aspect ratios used for a quantum device without necessity for removing in advance a surface oxide layer such as AS2O3, As2O, or Ga2O naturally formed on the surface of a GaAs layer and also without forming a dry etching mask for forming a miniaturized complex circuit: pattern. Disclosure of the Invention An electron beam micro/nano fabrication method of the present invention is for irradiating, onto a surface of a GaAs thin layer formed on an AlxGay ln1-x-yAszP1-z (0=x, y, z=1) surface including GaAs alone or an InP substrate, an electron beam controlled to an arbitrary electron beam diameter and current density so as to selectively substitute or generate Ga2O3 for a natural oxide layer formed on the GaAs surface, then dry-etching the GaAs layer surface by a bromide in single atomic layer units, and thereby selectively removing the natural oxide layer other than the part substituted by the Ga2O3, GaAs, and As such, for the electron beam micro/nano fabrication method of the present invention, it is unnecessary to fabricate and use a dry etching mask, which has been used at the time of dry etching, thus by changing Ga2O3 having etching resistance in crystallinity by controlling the amount of dose of an electron beam, it becomes possible to freely adjust the shape and aspect ratio of a pattern formed on the surface of AlxGay ln1-x-yAszP1-z layer. Therefore, it becomes possible to deal with a miniaturized circuit pattern, such as a circuit pattern used for recent quantum devices. Brief Description of the accompanying Drawings Fig. 1 is a diagram for explaining an embodiment example of an electron beam micro/nano fabrication method according to the present invention. Fig. 2 is a view showing micrographs of the surface of a substrate observed under an AFM according to respective amounts of dose of an electron beam of an electron beam micro/nano fabrication method according to the present invention. Fig. 3 is an enlarged view of Fig. 2 showing micrographs of the surface of a substrate observed under an AFM according to respective amounts of dose of an electron beam of an electron beam micro/nano fabrication method according to the present invention. Fig. 4 is a perspective view of Fig. 3 showing micrographs of the surface of a substrate observed under an AFM according to respective amounts of dose of an electron beam of an electron beam micro/nano fabrication method according to the present invention. Fig. 5 is a view showing a structural micrograph under an AFM indicating a difference in aspect ratios of microstructures formed when the amounts of dose of an electron beam are different. Best Mode for Carrying Out the Invention An electron beam micro/nano fabrication method according to an embodiment of the present invention is for irradiating, onto the surface of a GaAs thin layer formed on the surface of a AlxGay ln1-x-yAszP1-z layer including GaAs alone or an InP substrate, an electron beam controlled to an arbitrary electron beam diameter and current density so as to selectively substitute or generate Ga2O3 for a natural oxide layer formed on the GaAs layer surface, then dry-etching the GaAs and AlxGay ln1-x-yAszP1-z layer surface by a bromide in single atomic layer units, and thereby removing the natural oxide layer other than the part substituted by the Ga2O3, GaAs, and AlxGay ln1-x-yAszP1-z. In addition, anyof AsBr3, PBr3, GaBr3, and InBr3 is used for the bromide. In addition, by controlling etching resistance at the time of dry etching by controlling the amount of irradiation (amount of dose) of the electron beam and substituting Ga2O3 different in crystallinety for the GaAs natural oxide layer, micro/nano structures having different aspect ratios can be formed by a multi-chamber vacuum identical step. In addition, it is preferable that an acceleration voltage of the electron beam is 50keV or less and the amount of dose thereof is 1016 to 1020 electron/cm2. In addition, by an electron beam micro/nano fabrication method according to an embodiment of the present invention, onto a natural oxide layer on the surface of a GaAs thin layer formed on the surface of a AlxGay ln1-x-yAszP1-z layer, an electron beam controlled to an arbitrary electron beam diameter and current density is directly irradiated so as to selectively substitute chemically stable Ga2O3 for the natural oxide layer such as As203, As2O, or Ga2O naturally formed on the GaAs layer surface. Then, the other oxide such as As2O3, As2O, or Ga2O is selectively thermally desorbed under a depressurized environment of approximately 10-3Pa or less. At this time, the substituted stable oxide layer (Ga2O3) plays a role equivalent to a mask used for a conventional lithographic method, and when the AlxGay ln1-x-yAszP1-z. layer base material is etched in single atomic layer units in an atmosphere of a bromide such as As2Br3, PBr3, GaBr3, or InBr3r Ga2O3 being a chemically stable oxide layer remains on the surface of the AlxGay ln1-x-yAszP1-z. layer, thus an arbitrary pattern can be formed on the AlxGay ln1-x-yAszP1-z layer surface. Accordingly, by drawing an arbitrary pattern or the like on the AlxGay ln1-x-yAszP1-z layer surface at the time of electron beam irradiation by use of an electron beam, chemically stable Ga2O3 is formed on a portion of the AlxGay ln1-x-yAszP1-z layer surface irradiated with an electron beam, and this Ga203 remains without being etched by a bromide at the time of dry etching by a bromide, whereby it becomes possible to process an arbitrary pattern on the AlxGay ln1-x-yAszP1-z layer. In addition, by increasing the amount of dose of an electron beam at the time of electron beam irradiation, crystallinity of substituted Ga2O3 is improved, and mask resistance to dry etching also increases in accordance therewith, therefore, as a micro/nano structure formed after etching, one with a large aspect ratio can be formed. Namely, when the aspect ratio of a micro/nano structure formed after etching is to be increased, increasing the amount of dose of an electron beam makes it possible to control the line width and the like of a pattern on the AlxGay ln1-x-yAszP1-z layer surface in nano-order units. Here in after, an example of the embodiment of an ion beam micro /nano fabrication method according to this invention will be described with reference to the drawings. In Fig. 1, reference numeral 1 denotes a GaAs layer, and reference numeral 2 denotes a natural oxide layer on the surface of As2O3 or the like naturally formed on the surface of the GaAs layer 1. Also, in Fig. 1, it is shown that the amount of dose of an electron beam increases from left to right on the paper, that is, as it shifts to Fig. 1(a) to (c). By an electron beam micro/nano fabrication method according to the present embodiment example, first, without removing the natural oxide layer 2 such as As2O3 naturally formed on the surface of the GaAs layer 1, an electron beam is irradiated in a high vacuum toward the surface of this natural oxide layer 2 at an acceleration voltage of 50keV or less, and preferably, 20keV or less, so that the amount of dose becomes 1016xl020eletron/cm2. Here, the amount of dose of an electron beam is controlled by appropriately changing the amperage and irradiation time of the electron beam. By irradiating an electron beam, an oxide such as As2O3 or As203 of the natural oxide layer 2 is substituted by a chemically stable oxide 3 of Ga2O3. (see the upper tier of Pig. 1 (a) ) . Next, by raising the temperature of the GaAs layer 1 where a part of the surface oxide layer 2 has been substituted by the Ga2O3 3 to 580 to 620°C, the surface oxide layer 2 other than the part substituted by the Ga2O3 3 is thermally desorbed, and then by carrying out dry etching in single atomic layer units by etching the surface by irradiating thereon a bromide, the part other than the part substituted by the Ga2O3 3 is removed (see the lower tier of Fig. 1(a)). At this time, by applying patterning to the surface of the GaAs layer 1 so as to become a predetermined circuit pattern by use of an electron beam, it becomes possible to process an arbitrary pattern on the surface of the GaAs layer 1. Here, this dry etching makes it possible to obtain a surface excellent in flatness with excellent reproducibility. Concretely, in this etching by a bromide, atoms to be etched are atoms at step positions and kink positions of the surface, and since steps and kinks that compose a surface unevenness are preferentially removed, etching can be carried out in single atomic layer units. A surface obtained as a result of such etching in single layer units is extremely high in flatness. In other words, a flat surface can be obtained at the atomic level. Furthermore, this method allows isotropic etching regardless of plane indices. Therefore, for the surfaces of a GaAs crystal, it becomes possible to control, on the spot, etching in single layer units, namely, an etching depth and a profile shape of a processing region in nano-order units on all surfaces of (100), (110), and (111) regardless of plane indices. In this dry etching, etching can be carried out, by use of a bromide gas, in a ultra high vacuum, for example, after an evacuation to the level of 10-7Pa, by introducing an etenant gas (bromide gas) under a under a group V molecular gas partial pressure of 10"3 to 10-7Pa at 580 to 620°C. Here, as the bromide used as an etchant gas, preferably, AsBr3, which is a compound with As and PBr3, which is a compound with P, can be mentioned as representative examples thereof. As a matter of course, this may be of another type. As such, since it is possible to etch surface atomic layers with respect to every single layer, it becomes possible to process a part other than where a natural oxide layer that is present on the surface of an AlxGay ln1-x-yAszP1-z layer has been substituted by minute-sized chemically stable Ga2O3 formed by an electron beam irradiation in nano-order units, whereby micro/nano structures with high aspect ratios can be formed with excellent reproducibility and without difficulty, thus it becomes possible to carry out negative-tone lithography. By irradiating an electron beam 4 for a time longer than that of the aforementioned case to increase the amount of dose thereof, it becomes possible to increase the aspect ratio of the Ga2O3 3 as shown in Figs. 1 (b) and (c) . As such, by an electron beam micro/nano fabrication method according to the present invention, without removing a natural oxide layer such as AS2O3 naturally formed on the surface of a GaAs layer, by irradiating an electron beam onto this natural oxide layer, it becomes possible to form a chemically stable Ga2O3 on the surface. Then, by controlling the amount of dose of an electron beam, it becomes possible to control the crystallinity of Ga2O3 formed on the surface of the GaAs layer after dry etching by a bromide, whereby structures having different aspect ratios can be formed. In addition, by drawing, at the time of electron beam irradiation, on the surface of a GaAs layer so as to become a predetermined circuit by use of an electron beam, an arbitrary circuit pattern can be processed with excellent reproducibility. Thereby, it becomes possible to apply the method to wavelength discriminating devices, micro-machining, micro/nano fabrication of photonic crystals, micro-components, and the like, quantum wires, quantum boxes, and the like, not to mention semiconductor devices. Here, although a description has been given of a GaAs layer in the present embodiment example, effects similar to those of the GaAs layer described in the present embodiment example are provided as long as the layer is an AlxGay ln1-x-yAszP1-z layer, therefore, the invention is not limited to a GaAs layer. Hereinafter, the present invention will be described in grater detail based on an example. (Example) An electron beam whose electron beam diameter has been narrowed to 0.1µm is irradiated in a vacuum toward the surface of a natural oxide layer such as As2O3 naturally formed on the surface of a GaAs layer at an acceleration voltage of 30kV, and an amperage of 5xlO-7A for an irradiation time of 1 to 9 µsec/dot. At this time, lµm-wide lines were drawn by the electron beam at intervals of 10pm in a lattice form. In addition, by changing the irradiation time, the amount of dose was changed as follows: (1) 0. 6xl019electron/cm2 (2) 1. 2xl019electron/cm2 (3) 1.8xl019electron/cm2 (4) 2.4xl019electron/cm2 (5) 3.0xl019electron/cm2 (6) 3.6xl019electron/cm2 (7) 4.2xl019electron/cm2 (8) 4.8xl019electron/cm2 (9) 5.4xl019electron/cm2 After irradiating an electron beam at the above respective amounts of dose, the GaAs layer was introduced in an ultra-high vacuum unit, and after an evacuation to the level of 10-6Pa, the temperature is raised to 600°C, and after removing an oxide layer other than Ga2O3, etching was carried out for 17 minutes by introducing an AsBr3 gas under a gas partial pressure of 10~6 to 10-5Pa at 580°C. Fig. 2 to Fig. 4 show micrographs observed under an atomic force microscope (AFM) at the respective amounts of dose. Here, the respective numbers in the drawings correspond to the aforementioned respective amounts of dose. It can be understood from Fig. 2 through Fig. 4 that as the amount of dose of an electron beam increases, the line width of each pattern formed on the GaAs layer surface becomes wider. Consequently, by controlling the amount of dose of an electron beam, a circuit pattern having different line widths can be formed. In addition, Fig. 5 is a view showing a structural micrograph under an AFM indicating a difference in aspect ratios of micros true tures formed when the amounts of dose of an electron beam are different. As shown in Fig. 5, it can be understood from Fig. 5 that as the amount of dose of an electron beam increases, the aspect ratio becomes higher. Here, the respective numbers in the drawing correspond to the aforementioned respective amounts of dose of an electron beam. As in the above, by doping an electron beam into a natural oxide layer formed on the surface of a GaAs layer, chemically stable Ga203 that is not etched by a bromide can be formed, and furthermore, by controlling the amount of dose of an electron beam, it becomes possible to control the line width and aspect ratio of a pattern formed on the GaAs layer surface and carry out processing in nano-order units through a series of steps by use of an identical device. Accordingly, it becomes possible to considerably lower the manufacturing cost. As has been described in detail in the above, by the present invention, without removing a natural oxide layer naturally formed on the surface of a semiconductor crystal including a compound substrate such as an AlxGayIni_x_yAszPi_z layer, by doping an electron beam into the natural oxide layer, chemically stable Ga2O3 that is not etched by a bromide and that is high in crystallinity can be formed. Therefore, an arbitrary circuit pattern can be processed on the surface without using an etching mask at the time of etching as conventionally. Furthermore, by controlling the amount of dose of an electron beam, it becomes possible to process the line width and aspect ratio of a pattern formed on the AlxGay ln1-x-yAszP1-z layer in nano-order units. Moreover, the present invention is not limited to the embodiment and example as described above. Various other embodiments and examples without departing from the spirit and scope of the present invention can be made. Industrial Applicability According to the present invention, it becomes possible to realize a useful element that makes the best use of various quantum device characteristics, for example, a quantum wire, a quantum box, a diffraction grating, and a micro-machine. WE CLAIM : 1. An electron beam micro/nano fabrication method for allowing negative- tone lithography for irradiating, onto a surface of a GaAs thin layer formed on an AlxGay ln1-x-yAszP1-z (0=x, y, z=1) surface comprising GaAs alone or an InP substrate, an electron beam controlled to an arbitrary electron beam diameter and current density so as to selectively substitute or generate Ga2O3 for a natural oxide layer formed on the GaAs surface, then dry-etching the GaAs layer surface by a bromide in single atomic layer units, and thereby selectively removing the natural oxide layer other than the part substituted by the Ga2O3, GaAs, and AlxGay ln1-x-yAszP1-z wherein an acceleration voltage of the electron beam is 50keV or less and the amount of dose thereof is 1016 to 1020 electron/cm2, and microstructures having different aspect ratios can be formed by an identical step by controlling the amount of dose of an electron beam by controlling the amount to be etched at the time of dry etching by controlling the amount of irradiation of the electron beam and thereby generating Ga2O3 different in crystallinity on the GaAs layer surface. 2. The electron beam micro/nano fabrication method as claimed in Claim 1, wherein any of AsBr3, PBr3, GaBr3, and lnBr3 is used for the bromide. 3. The electron beam micro/nano fabrication method as claimed in Claim 1 or 2, wherein the AlxGay ln1-x-yAszP1-z layer surface is controlled on the spot in terms of an etching depth and a profile shape of a processing region in nano-order units by controlling the amount of irradiation of the electron beam. An electron beam microprocessing method is disclosed where in the surface of an AlxGay ln1-x-yAszP1-z (0≤x, y,z≤1) layer (1) containing GaAs as a simple substance and an lnP substrate is irradiated with an electron beam (4) having abritrary electrom beam diameter and current dentisty, so that a natural oxide film (2) formed on the AlxGay ln1-x-yAszP1-z |ayer surface is selectively substituted with or formed into Ga2O3 (3), and then the AlxGay ln1-x-yAszP1-z layer surface is dry-etched using a bromide in single atom layer unit, thereby removing the natural oxide film other than the portion substituted with Ga2O3 and the AlxGay ln1-x-yAszP1-z substrate.

Documents:

2395-KOLNP-2005-CORRESPONDENCE 1.1.pdf

2395-KOLNP-2005-CORRESPONDENCE.pdf

2395-KOLNP-2005-FORM 27-1.1.pdf

2395-KOLNP-2005-FORM 27.1.2.pdf

2395-KOLNP-2005-FORM 27.pdf

2395-KOLNP-2005-FORM-27.pdf

2395-kolnp-2005-granted-abstract.pdf

2395-kolnp-2005-granted-assignment.pdf

2395-kolnp-2005-granted-claims.pdf

2395-kolnp-2005-granted-correspondence.pdf

2395-kolnp-2005-granted-description (complete).pdf

2395-kolnp-2005-granted-drawings.pdf

2395-kolnp-2005-granted-examination report.pdf

2395-kolnp-2005-granted-form 1.pdf

2395-kolnp-2005-granted-form 18.pdf

2395-kolnp-2005-granted-form 3.pdf

2395-kolnp-2005-granted-form 5.pdf

2395-kolnp-2005-granted-gpa.pdf

2395-kolnp-2005-granted-reply to examination report.pdf

2395-kolnp-2005-granted-specification.pdf

2395-KOLNP-2005-PETITION UNDER RULE 137.pdf

2395-KOLNP-2005-PETITION UNDER RULE 138.pdf