Deposition Processes
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onth's articles continue the sequence of ways to deposit films, the general direction being toward lower substrate temperatures. Along with the freedom to extensively vary thin film characteristics, resulting properties and applications comes the difficulty in understanding preparation-characterization-property relations in enough detail to control and reproduce deposition processes. The N o v e m b e r articles covered molecular dynamics computer modeling of nucleation and growth processes, molecular beam epitaxy, organometallic v a p o r p h a s e epitaxy, a n d chemical vapor deposition. This month's articles c o n t i n u e t h e s e q u e n c e of w a y s to d e p o s i t films, the general direction being toward lower substrate temperat u r e s . P l a s m a s , w h i c h offer b o t h
MRS BULLETIN/DECEMBER 1988
increased flexibility and complexity, are primarily considered. The last article covers thermal plasmas, not to control the vapor deposition but to melt powders which result in a multiple splatquenched array of particles that form coatings important to industry. • R.F. Bunshah and C.V. Deshpandey (University of California at Los Angeles) consider the broad topic of evaporation processes. They show that, although evaporation is one of the earliest and simplest deposition processes, many variations for thin film preparation are in use. After covering the theory, mechanisms, and approaches to evaporation, they detail the two more technologically important processes involving electron-beam-heated sources and arc evaporation sources. They discuss the wide range of elemental, alloy, and compound materials that can be prepared and show how reactive and activated reactive evaporation (ARE) processes are often used to obtain this wide range of materials. The ARE process, which was pioneered by Bunshah, uses thermal evaporation and plasmas to generate and control gas phase species and the energy of the species during growth. The article is an excellent lead-in to the other plasma-based deposition processes considered in this issue. • S.M. Rossnagel and J.J. Cuomo (IBM T.J. Watson Research Center) review the importance of independent control of ion bombardment by the use of sources such as the extensively used Kaufman-ion source. Using examples from the literature they show how controlled energy and flux of the ion bombardment during deposition can modify film grain size, nucleation density, defects, crystal structure lattice spacing, preferred crystallite orientation, density, and stress. In addition to physical processes at growing film surfaces, ion beams can control surface chemistry through the use of
reactive species. Although just several years ago we thought such ion beam sources to be mainly of use in small-scale research deposition systems, the authors indicate that their use in large-scale deposition processing will become more prominent. • W.D. Westwood (Bell Northern Research) points out the long history of sputter deposition processes and notes that the introduction of magnetron sputtering systems
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