Gasless ion plating

Abstract

Abstract A gasless ion plating process wherein plating material is melted, vaporized, and then subjected to an ionization environment in a low pressure chamber with a "virtual cathode" consisting of a plasma of ionized atoms of evaporant material created by evaporating in an RF field. It is a gasless ion plating process wherein the system ambient pressure prior to plating material evaporation may be much lower than that required to sustain a glow discharge, however, with vapor pressure of evaporant material added to the environment base pressure being such as to result in a plasma of ionized atoms of the plating material developing as the vaporized material approaches the RF cathode. This invention relates in general to high particulate energy level ion plating deposition of plating material, and in particular, to gasless ion plating. Various high-rate ion plating sources advantageously suited to applicant's gasless ion plating process are disclosed in applicant's co-pending application entitled, "High Rate Ion Plating Source," Application Ser. No. 551,703, filed Feb. 21, 1975, in addition to electron gun, filament and boat type sources, among other known sources. In the application of protective coatings to substrates, vacuum evaporation systems, sputtering, and classical ion plating have been used in the past with varying degrees of success. Vacuum evaporation provides high deposition rates, but has the disadvantage of being a "line-of-sight" process. Three-dimensional uniformity is very difficult to achieve and requires expensive tooling--and such deposited coating results in poorly bonded columnar grains. Further, since there is no particle acceleration involved in the vapor deposition, adhesion can frequently be a problem. To some extent, sputtering overcomes the "line-of-sight" problem, and offers a wide variety of materials, film stoichiometry, and generally better adhesion, than does vapor deposition. There are, however, serious problems with slow deposition rates and three-dimensional uniformity. An often overlooked problem with sputtering is the decreased energy of the deposited atom. Sputtering is a secondary process. An ion of inert gas is born in a plasma, at a space charge depression of typically +80 to +100 volts. Only after an inelastic collision with the target, is an atom of target material released for useful coating. The neutral atom must then migrate back across the dark space, through the plasma, onto the substrate. In the process, numerous collisions deplete the atom's energy. Thus, in its journey to the substrate, the inert gas that heretofore has been considered essential for maintaining the plasma and removing the target material, becomes a hindrance to the liberated atom of coating material. Additionally, a considerable amount of this inert gas becomes included in the deposited film. Classical ion plating--as described, for example, in Mattox, U.S. Pat. No. 3,329,601--provides some of the advantages of the previous two methods, but is entirely dependent upon an inert gas that is introduced into the system to maintain the plasma. The classical ion plating system ionizes only about 20% of the evaporated material. Further, the full effect of the gas upon the coating and/or substrate is unknown. It is therefore a principal object of this invention to provide an improved plating system. Another object is to provide a plating system with high deposition rates. A further object is to provide a plating system not subject to degradation caused by inert gases. A still further object is to provide a plating system which coats small internal diameters and irregularly shaped cavities of a substrate. Still another object of this invention is to provide a plating process for plating a wide variety of materials, both conductive and non-conductive. Features of this invention useful in accomplishing the above objects include a plating system utilizing a high rate ion source, operable in a vacuum. The ion source is instrumental in converting the plating material to the form of a plasma forming a "virtual" cathode in the region of the substrate. A specific embodiment representing what is presently regarded as the best mode of carrying out the invention is illustrated in the accompanying drawing:

Inventors

• 👤 Gerald W. White

Bibliographic Details