Effect of Process Conditions and Chemical Composition on the Microstructure and Properties of Chemically Vapor Deposited
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EFFECT OF PROCESS CONDITIONS AND CHEMICAL COMPOSITION ON THE MICROSTRUCTURE AND PROPERTIES OF CHEMICALLY VAPOR DEPOSITED SiC, Si, ZnSe, ZnS AND ZnS.Se,.. MICHAEL A. PICKERING, RAYMOND L. TAYLOR, JITENDRA S. GOELA AND HEMANT D. DESAI, Morton International, 185 New Boston Street, Woburn, MA 01801 ABSTRACT Sub-atmospheric pressure chemical vapor deposition (CVD) processes have been developed to produce theoretically dense, highly pure, void-free and large area bulk materials, SiC, Si, ZnSe, ZnS and ZnS.Se,_1 . These materials are used for optical elements, such as mirrors, lenses and windows, over a wide spectral range from the vacuum ultraviolet (VUV) to the infrared (IR). In this paper we discuss the effect of CVD process conditions on the microstructure and properties of these materials, with emphasis on optical performance. In addition, we discuss the effect of chemical composition on the properties of the composite material ZnS. Sel.5 . We first present a general overview of the bulk CVD process and the relationship between process conditions, such as temperature, pressure, reactant gas concentration and growth rate, and the microstructure, morphology and properties of CVD-grown materials. Then we discuss specific results for CVDgrown SiC, Si, ZnSe, ZnS and ZnSSel-.. INTRODUCTION Chemical vapor deposition (CVD) is a well known process to produce theoretically dense crystalline materials for a variety of applications [1-41]. This process has been used to produce metal films (W, Al, Mo, Au, Cu, Pt) for protective coatings [1-5]; ceramic materials (A120 3, TiC, SiC, B4C, TiB 2, HfC, HfN) used for hard or diffusion barrier coatings [6-11]; semiconductors (GaAs, GaP, InP, PbS, Si) with required doping [12-16]; refractory oxides (ZnO2) used for thermal barrier [6,17]; films (BN, MoSi 2, SiC, B4C) for protection against corrosion [18-20]; powders (Si3N4 , SiC) used to fabricate complicated shaped parts by sintering or hot-pressing [1]; materials (Si, GaAs, HgCdTe, CdZnTe) for solid state and energy conversion devices [21-24]; fibers (B, B4C, SiC) used to fabricate composite materials [24]; transmissive infrared optical materials (ZnSe, ZnS, CdS, CdTe, ZnSSel..) [25-31]; and monolithic ceramic materials (S3N4, SiC, Si) [32-41]. Five major types of products have been made via CVD technology. These are fibers, thin film coatings, powders, monolithic structures and composites. While there has been much CVD technology development and understanding for the first three types of products, less attention has been directed toward monolithic and composite materials. However, recently there has been a growing interest in developing CVD technologies to produce monolithic optical substrates and structural ceramic composite materials. The CVD process is capable of producing theoretically dense, high purity and homogeneous materials. This, combined with the fact that the process is readily scalable, makes it attractive for producing high performance optical Mat. Res. Soc. Symp. Proc. Vol. 250. ,11992 Materials Research Society
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