|Title of Invention||
A PROCESS OF COATING HIGH TEMPERATURE REFRACTORY MATERIALS ONTO A SUBSTRATE
|Abstract||A process of coating high temperature refractory materials onto a substrate, said process comprising the following steps: (a) locating at least one filament of the material to be coated and the substrate in an air tight chamber adapted to handle suibatmospheric pressures; (b) reducing the pressures in said chamber to between 10-1to 10-3 torr; (c) heating the said filament/s to a temperature above 1200 degrees C and below the melting point of the filament/s; (d) heating said substrate to about 400 degrees C; (e) introducing an oxidizing gas and a reducing gas in said chamber while maintaining the pressure inside said chamber below 300 torr; and (f) maintaining the flow of said oxidizing gas and said reducing gas for a predetermined time to obtain a coating on said substrate of thickness in direct proportion to time.|
|Full Text||FORM - 2
THE PATENT ACT, 1970
(39 of 1970)
THE PATENT RULES, 2003
(See section 10 and Rule 13)
a) GODBOLE VIJAY PURUSHOTTAM
An Indian National
of 2032 Sadashiv Peth, Tilak Road, 6-Aparna Apt.Near Mastek Ltd.,
Pune-411 030, Maharashtra, India;
b) GUPTE ANIL SHANKAR
An Indian National
of Flat No. 101, Kalpita Apartments, Prabhat Road, Lane No. 10th,
Pune-411 004, Maharashtra, India; and
c) GODBOLE RHUSHIKESH VIJAY
An Indian National
Of C/o. Multi-Tech Corporation, Varadan, Plot No. 20, Girish Society, S. No. 6, 17, 125,
Off. NDA Road, Near old Warje-Toll Post, Warje, Pune-411 052, Maharashtra, India.
THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION
Field of the invention:
This invention relates to metal coatings. In particular, this invention relates to metal coatings of high melting temperature materials.
Coatings of metal either on metals or alloys are carried out for various
reasons, like enhancing aesthetic or functional utility of the base
Thin layer of metal coating on suitably prepared base material is
typically obtained by either dip process, electro plating methods or
chemical vapour deposition process.
Typical examples of dip process include galvanising of iron sheets,
covering of silver ornaments with gold coating. Decorative chrome
plating is done by an electrolytic deposit process and is extensively used
in automobile and electrical component manufacturing industries.
Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile byproducts are also produced, which are removed by gas flow through the reaction chamber.
Micro-fabrication processes widely use CVD to deposit materials in various forms, including: mono crystalline, poly crystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon
nanofibers, filaments, carbon nanotubes, Silicon dioxide, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxy-nitride, titanium nitride, and various high-k dielectrics. The CVD process is also used to produce synthetic diamonds.
Chemical vapor deposition methods are in wide use and these processes differ in the means by which chemical reactions are initiated and the process conditions.
CLASSIFIED BY OPERATING PRESSURE
Atmospheric pressure CVD (APCVD) - CVD processes at atmospheric pressure.
Low-pressure CVD (LPCVD) - CVD processes at sub atmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer. Most modern CVD process are either LPCVD or UHVCVD.
Ultrahigh vacuum CVD (UHVCVD) - CVD processes at a very low pressure, typically below 10-6 Pa (~ 10-8 torr).
CLASSIFIED BY PHYSICAL CHARACTERISTICS OF VAPOR
Aerosol assisted CVD (AACVD) - A CVD process in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically.
Direct liquid injection CVD (DLICVD) - A CVD process in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors. Then the precursor vapours are transported to the substrate as in classical CVD process. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.
Plasma-Enhanced CVD (PECVD) - CVD processes that utilize a plasma to enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors.
Remote plasma-enhanced CVD (RPECVD) - Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature.
Atomic layer CVD (ALCVD) - Deposits successive layers of different substances to produce layered, crystalline films.
Hot wire CVD (HWCVD) - Also known as Catalytic CVD (Cat-CVD) or hot filament CVD (HFCVD). Uses a hot filament to chemically decompose the source gases
Metal-organic chemical vapor deposition (MOCVD) - CVD processes based on metal-organic precursors.
Rapid thermal CVD (RTCVD) - CVD processes that use heating lamps or other methods to rapidly heat the wafer substrate. Heating only the substrate rather than the gas or chamber walls helps reduce unwanted gas phase reactions that can lead to particle formation.
The conventional CVD process for fabrication of coatings of high melting temperature materials such as Tungsten, Molybdenum, and/or their carbides etc. are cumbersome because of involvement of hazardous chemicals, complicated chemical reactions and environmental pollution.
Objects of the Invention:
One of the objects of the present invention is to provide a hot wire chemical vapour deposition process suitable for high melting temperature materials.
Another object of the present invention is to provide a hot wire chemical vapour deposition process that is simple and non- hazardous.
Another object of the present invention is to provide a hot wire chemical vapour deposition process that does not involve complicated chemical reactions.
Another object of the present invention is to provide a hot wire chemical vapour deposition process that does not cause environment pollution.
SUMMARY OF THE INVENTION:
This invention discloses a simple and novel method by which it is possible to obtain thin/thick coatings of refractory and other metal coatings, their carbides, oxides and/or composites.
In this process, in a closed chamber and at sub-atmospheric pressures, the mixture of hydrogen, and/or hydrocarbon (e.g. methane gas), and oxygen gas, in specific proportion, is flown over heated wire/s of parent metal to initiate pyrolytic re-dox processes. This leads to gasification of wire-material in form of molecules of metal compound. The work-piece is positioned sufficiently near to the heated wires. The molecules of metal compound settle on surface of work-piece. Further reactions also occur at the surfaces of work-piece leading to thin/thick coatings of parent metal (wire-metal), or its carbide, oxide, depending upon the composition of gas mixture. For required coating material, the chemical reactions can also initiated in step/s by appropriately changing gas composition for different time duration. The thickness and morphology of coatings depend upon the time of processing, process parameters and thermo-dynamical properties of given material.
Typically, the process could be carried out in a closed stainless steel chamber at pressures of 10-200 Torr. The metal wires are heated in excess of 1200-
1500°C by resistive heating, wherein the specific value of temperature depends upon the type of metal wire. The pure oxygen and hydrocarbon gases are diluted in excess amount of hydrogen gas, up to a few percent (by volume). The flow rate of gas mixture could be adjusted ~ 50-200 standard cubic centimeter per minute (seem). The temperature of work-piece is kept in excess of 500-700°C. Typical coating thickness are in the range of 50 nm to 30 microns and preferred range of coating thickness are 1 to 10 microns. The chamber pressures, the temperatures and the gas flow rates are measured by capacitance gauge, thermocouple/pyrometer, and mass flow controllers (MFC's), respectively.
The chamber pressures are controlled by appropriate throttle valve positioned in vacuum line from chamber to vacuum pump. At nominally optimized conditions, the efficiency of re-dox reactions determine the rate of deposition. Typically, the coatings such as of tungsten, molybdenum can be fabricated at the rate of ~ 5-20 micro-meters (um) per hour. The adhesion of coatings on the work-piece depends upon the extent of interface reactions between work-piece material and coating material. For example, adhesive coatings of tungsten, molybdenum, and their carbides can be obtained on ceramic materials such as Alumina. The results of this invention are well supported by various types of characterization methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of X-rays (EDX), X-ray Photo-electron Spectroscopy (XPS) and the like.
While considerable emphasis has been placed herein on the particular features of "hot wire chemical vapour deposition process" and the
improvisation with regards to it, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiment without departing from the principles of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
|Indian Patent Application Number||1423/MUM/2007|
|PG Journal Number||13/2014|
|Date of Filing||24-Jul-2007|
|Name of Patentee||GODBOLE VIJAY PURUSHOTTAM|
|Applicant Address||2032, SADASHIV PETH, TILAK ROAD, 6-APARNA APT., NEAR MASTEK LTD., PUNE|
|PCT International Classification Number||CO318/00|
|PCT International Application Number||N/A|
|PCT International Filing date|