Rapid Growth of Ceramic Films by Particle-Vapor Codeposition*
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RAPID GROWTH OF CERAMIC FILMS BY PARTICLE-VAPOR CODEPOSITION* ROBERT H. HURT AND MARK D. ALLENDORF Combustion Research Facility, Sandia National Laboratories, 8361 Livermore, California 94551-0969 * This work is supported by the Support of the Department of Energy Office of Conservation Advanced Industrial Materials Program. ABSTRACT Particle-enhanced chemical vapor deposition (PECVD) is capable of producing ceramic films at high deposition rates. A mathematical model of the particle-vapor codeposition process has been developed and has been applied to PECVD processes to predict deposition rate enhancements and deposit properties. I. INTRODUCTION Recently, substantial increases in the rate of chemical vapor deposition of TiO 2 , ZrO2, and AIN have been reported by introducing particles into the CVD process [1,2]. Improvements in AIN deposition rates of up to two orders of magnitude have been obtained with this technique. In general, particles may be introduced in the form of an aerosol, generated in situ by a controlled amount of gas-to-particle conversion (homogeneous nucleation), or in the form of an entrained powder, independently charged to the reactor [31. In this article, processes in which the rate of CVD is enhanced by the codeposition of particles, achieved either by seeding the gas phase or by in situ aerosol formation, will be referred to generically as "Particle-Enhanced Chemical Vapor Deposition" or PECVD processes. The structure of deposits formed by this technique is depicted in Figure 1. It is believed [1] that reactions of gas-phase species occur on the enhanced surface area of a porous region at the interface between the growing deposit and the gas phase. There is a close relation between this process and chemical vapor infiltration (CVI) processes [4], in which porous bodies (formed, for example, from compressed powders) are densified by internal CVD growth, the difference being that in PECVD the porous body is formed gradually with CVI-type densification occurring simultaneously in a restricted region at the porous interface of the growing deposit. In the existing literature there have been numerous studies of particle deposition and of vapor deposition processes and their applications. There has not, however, to the authors' knowledge, been a theoretical treatment of the particle-vapor codeposition process and, as a result, the factors determining the growth rate and properties of such deposits are not well established. In the present article, a random sphere formulation is developed and used in a unified treatment of both PECVD subprocesses: particle deposition and densification of porous media by vapor deposition. II. SUMMARY OF THE RASSPVDN MODEL DEVELOPMENT In this section, the development of the "lRandom Sphere Model of Simultaneous Particle and Vapor Deposition" or "RASSPVDN" is summarized. The complete development can be found elsewhere [5]. The model considers the local particle-vapor codeposition process, isolated from processes occurring prior to deposition, such as nucleation and gro
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