Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-12-22
2001-04-10
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192120, C204S192160, C204S192170, C204S192230, C204S298120, C204S298130, C419S002000, C419S010000, C419S023000, C419S031000, C419S032000, C419S029000, C419S042000, C419S047000, C419S048000, C419S049000, C428S428000, C428S433000, C428S457000, C428S539500, C428S689000, C264S042000, C264S043000, C264S050000, C420S578000
Reexamination Certificate
active
06214177
ABSTRACT:
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH
Not applicable.
FIELD OF THE INVENTION
The invention relates generally to target materials used in sputtering processes, and more particularly to a method of preparing a target material for use in sputtering processes to coat glass.
BACKGROUND OF THE INVENTION
Sputtering is an electric discharge process used to synthesize materials while imparting certain characteristics thereto. For example, sputtering may be used to synthesize glass while, concurrently, providing the glass with characteristics such as emissivity, reflectivity, transmittance, chemical resistance or color.
During the sputtering process, gas ions bombard a target having a face formed of a desired material that is to be deposited or coated as a thin film or layer on a substrate. The ion bombardment of the target causes atoms or molecules of the target material to be ejected (or “sputtered”) onto the substrate to synthesize a material. The target may be specifically selected in view of the material to be synthesized and the characteristics to be provided to the synthesized material.
Silicon-aluminum alloys are often used as targets in sputtering processes to synthesize glass because the addition of the aluminum advantageously increases the electrical conductivity of the silicon. But, current methods for preparing such silicon-aluminum targets frequently result in targets that have several shortcomings which translate into serious drawbacks in glass synthesized using those targets.
Conventional silicon-aluminum targets are prepared by vacuum casting methods in which the targets are solidified from a 100% liquid state. This preparation technique results in target materials having certain undesirable characteristics such as grain size control difficulty, heterogeneity, or segregation. In turn, glass sputter-coated using these targets tends to have defects visible in the coating, thus rendering the glass useless.
A characteristic that is particularly undesirable, yet also difficult to avoid during vacuum-casting preparation of a silicon-aluminum target, is residual porosity at the center of the target. A sputtering process that is carried out with a silicon-aluminum target having a residual porosity of as little as 0.5 millimeters in diameter at the center of the target could cause electrical arcing during the sputtering process. In turn, glass sputter-coated using a silicon-aluminum target with residual porosity, has a reduced yield, and exhibits visible defects in the coating.
It would, therefore, be desirable to provide a silicon-aluminum sputtering target and a method for fabricating such a target, which provide certain enhanced characteristics to glass sputter-coated using the target.
SUMMARY OF THE INVENTION
The present invention provides a silicon-aluminum sputtering target and a method for producing such a target. Although the invention is primarily shown and described with reference to a method for preparing a silicon-aluminum sputtering target for use in the synthesis of glass, it is understood that the method has other applications as well.
In one embodiment, a powder base of silicon and aluminum metallic precursors are blended together. The blended base is placed in a metal containment unit which is heated under vacuum to eliminate a predetermined amount of residual moisture. The containment unit is then sealed and placed in a treatment unit. The silicon-aluminum base is heated and pressurized in the treatment unit until it is consolidated and sufficiently densified so as to form a silicon-aluminum sputtering target for use in synthesizing glass.
The powder base preferably includes between about 80% to about 95% silicon and about 5% to about 20% aluminum. The heating and pressurization of the powder base preferably occurs in a hot isostatic press at a pressure greater than about 3000 psi and at a temperature above about 580° C. (1076° F.), the silicon-aluminum eutectic melting point, but below about 815° C. (1500° F.). This temperature range prevents more than 30% liquid phase silicon-aluminum from being present during the preparation of the silicon-aluminum target, but also allows for sufficient liquid phase to be present in order to effect densification. By limiting the amount of liquid phase silicon-aluminum therein, the target has reduced residual porosity, has a substantially uniform chemistry, and is not brittle. The target, in turn, provides certain enhanced characteristics to glass that is sputter-coated using the target.
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SISPA ™Silicon Alloy Targets for ReactiveSi3N4/SiO2Coatings, Leybold Materials Inc. (Date Unknown).
Diamond Alan
Nutter & McClennen & Fish LLP
Ultraclad Corporation
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