Selective Area Chemical Vapor Deposition of Si[sub 1−x]Ge[sub x] Thin Film Alloys by the Alternating Cyclic Method: A Thermodynamic Analysis. II. The System Si-Ge-Cl-H-Ar

Abstract

As a starting point, for a system of minimum chemical complexity, the analysis of the Si-Ge-Cl-H system 1 is a good introduction for setting up an experimental alternating cyclic (A.C.) process. However, in the experimental implementation of such a system, it may be somewhat difficult to reestablish flow equilibrium every time the hydrogen flow is terminated abruptly and then restarted, particularly if on-off cycles are very short. Experimentally, it would be advantageous to have a continuous flow of an inert carrier gas present, such as argon, to act as a flow rate buffer to the abrupt hydrogen flow cycling and to minimize back diffusion. 2 In the present paper we discuss the effect of including an inert gas such as argon on the behavior of the Si-Ge-Cl-H system. This paper describes thermodynamic analysis of the Si-Ge-Cl-H-Ar system and employs a first principles analysis as an integrity check. The approach is identical to that employed for the Si-Ge-Cl-H system described in Ref 1. In addition, the several potential advantages in using an inert carrier gas such as argon are discussed, and this was the system employed for the experimental studies described recently. 3,4 The Si-Ge-Cl-H-Ar System The Si-Ge-Cl-H-Ar system contains five chemical components (Si, Ge, Cl, H, Ar) present in two phases (vapor and solid). From the Gibbs' phase rule, the system possesses five degrees of freedom. The five independent variables can be chosen as total system pressure, p t , three different hypothetical component partial pressure ratios, e.g.,