Coating processes – Direct application of electrical – magnetic – wave – or... – Chemical vapor deposition
Reexamination Certificate
1999-08-31
2001-01-16
Meeks, Timothy (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Chemical vapor deposition
C427S596000, C427S597000, C427S248100, C427S250000
Reexamination Certificate
active
06174571
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to methods for applying protective coatings of a desired composition on articles by physical vapor deposition.
The thermal evaporation and condensation of solid materials, such as metals, ceramics and inorganic compounds, to form layers is a developed art. There are many prior art techniques and apparatuses that permit such materials to be evaporated from a source and condensed to form a layer on a substrate that is disposed a distance from the source. The processes involve heating a material to be evaporated to a temperature at which it has a significant vapor pressure, thus creating a vapor stream. Heating techniques include direct heating methods, such as heating the material to be deposited directly using resistance, induction, electron beam or lasers to melt all or some portion of the material to be evaporated, or indirect heating methods, such as by heating the surface of a higher melting material and flashing the material to be evaporated off the hot surface.
A coating composition is related to the composition of the evaporant source. Typically, substrates are positioned perpendicularly above, (i.e., in “line-of-sight”), of a vapor source for coating thereby. Different coating compositions at the line-of-sight position can be achieved by varying the composition of the evaporant source.
Generally, the evaporant source should be replenished as material is gradually consumed during the evaporation process. In this respect, where the vapor source is a molten pool held in a crucible, the bottom of the crucible can be adapted to provide an opening for receiving the continuous feed of a solid bar or ingot of the evaporating material. The evaporant source composition and, therefore, coating composition are dependent on the composition of the ingot. Accordingly, a desired coating composition at the line-of-sight position can be achieved by controlling ingot composition.
In some cases, depending on the materials involved, ingot composition is dictated by fabrication considerations. For instance, for a given group of materials, attempt to manufacture ingots of certain compositions will result in ingots that are unduly brittle or otherwise mechanically unsuitable. In such cases, control of ingot composition is severely limited and, therefore, control of coating composition at the line-of-sight is more difficult. Therefore, a need exists for a process to deposit materials for controlling the deposit composition.
SUMMARY OF THE INVENTION
It has been determined that the chemical composition of a deposited material on a substrate that is deposited by vapor deposition can vary from the chemical composition of the vapor source, and in particular can be caused to vary as a function of horizontal displacement of the substrate from a line normal to the surface of a vapor source. Accordingly, in order to be able to obtain a coating of a consistent, desired composition with an evaporant source of a fixed chemical composition, the invention provides a method of forming evaporated deposits of a desired composition on a plurality of workpieces, comprising the steps of:
i) disposing a plurality of workpieces above a vapor source, each workpiece positioned at a first vertical distance above the vapor source and at a first horizontally-disposed distance from a line extending perpendicularly upward from the vapor source, to provide a deposit thereon of a desired composition;
ii) heating the vapor source in a vacuum and evaporating a part of the vapor source; and
iii) condensing deposits evaporated from the vapor source on the workpieces.
The distances may be obtained in a number of ways. In one embodiment of the method of the invention, the such first vertical distance above the vapor source and the first horizontally displaced distance from the line corresponds to those distances determined by the following steps, namely:
(i) disposing an elongate test specimen a spaced distance above a vapor source so that the test specimen possesses a surface extending horizontally from a line extending perpendicularly upward from the vapor source to a position horizontally displaced from the line;
(ii) heating the vapor source in a vacuum to evaporate the vapor source;
(iii) condensing a deposit evaporated from the vapor source on the surface of the test specimen;
(iv) measuring the chemical composition of the deposit on the surface at various horizontally displaced positions thereon relative to the line; and
(v) selecting a desired horizontally displaced distance as a the horizontally-displaced distance that provides a deposit of the desired chemical composition.
In another embodiment for determining the first vertical distance above the vapor source and the first horizontally displaced distance from the line, the distances are determined by the following steps:
(i) disposing a test specimen a spaced distance above a vapor source so that the test specimen possesses a surface extending horizontally from a line extending perpendicularly upward from the vapor source to a position horizontally displaced from the line;
(ii) heating the vapor source in a vacuum to evaporate the vapor source;
(iii) condensing a deposit evaporated from the vapor source on the surface of the test specimen;
(iv) measuring the chemical composition of the deposit on the surface at various horizontally displaced positions thereon relative to the line; and
(v) selecting a desired horizontally displaced distance for the workpieces as a horizontally-displaced distance that provides a deposit of the desired chemical composition at the spaced distance above the vapor source.
Another aspect of the present invention for determining the first vertical distance above the vapor source and the first horizontally displaced distance from the line, the distances are determined by the following steps:
(i) disposing a test specimen a spaced distance above a vapor source and a horizontally spaced distance from a line extending perpendicularly upward from the vapor source from the line;
(ii) heating the vapor source in a vacuum to evaporate the vapor source;
(iii) condensing a deposit evaporated from the vapor source on the test specimen;
(iv) measuring the chemical composition of the deposit on the specimens;
(v) repeating steps (i) to (iv) above, in each instance locating the test specimen a different horizontally spaced distance from the line; and
(vi) selecting as a desired horizontally displaced distance and vertical spaced distance for the workpieces the horizontally-displaced distance and vertically spaced distance that provided a deposit of the desired chemical composition on a test specimen.
REFERENCES:
patent: 4701592 (1987-10-01), Cheung
patent: 5993904 (1999-11-01), Boucher
“An Algorithm for Optimization of Experimental Parameters for Maximum Uniformity of Film Thickness,” Ramprasad, B.S., Radha, T.S., and Ramakriskna Rao, M., J., Vac. Sci. Technol. 9 (3) 1104-05 (1972). (No month).
“The Deposit of Films of Uniform Thickness for Interferometer Mirrors,” Fisher, R.A., Platt, J.R. Rev. Sci. Instrum 8 505-7 (1937). (No month).
“On Uniformity of Film Thickness on Rotating Substrates,” Ramprasad, B.S., Radha, T.S., and Ramakriskna Rao, M., Vac. Sci. Technol. 9 (4) 1227-28 (1972). (No month).
“Thickness Distribution and Step Coverage in a New Planetary Substrate Holder Geometry,” Behrndt, K.H. J. Vac. Sci. Technol. 9 (2) 995-1007 (1972). (No month).
“Optimum Geometry for Uniform Deposits on a Rotating Substrate from a Point source,” Ramprasad, B.S., Radha, T.S., Vacuum 24 (4) 165-66 (1974). (No month).
“The distribution of Thin Films Condensed on Surfaces by the Vacuum Evaporation Method,” Holland, L. and Steckelmacher. W., Vacuum 11 (4) 346-64 (1952) (No months).
“Optical Applications of Dielectric Thin Films,” Lissberger, P.H., Rept. Prog. Phys. 33, 197-268 (1970). (No month).
“Distributing and Apparent Source Geometry of Electron-Beam-Heated Evaporation Sources,” E.B. Graber, J. Vac. Sci. Technol. 10 (1) 103-03 (1973). (No month).
“A Spatial Distribution Study of A Beam Vapour Emitted by Electron-
Corderman Reed Roeder
Nardi, Jr. Richard Arthur
General Electric Company
Johnson Noreen C.
Meeks Timothy
Stoner Douglas E.
LandOfFree
Method of using a substrate offset to obtain a specific... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of using a substrate offset to obtain a specific..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of using a substrate offset to obtain a specific... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2454229