Simple method for the calculation and use of CVD phase diagrams with applications to the Ti-B-Cl-H system, 1200 to 800/sup 0/K

Abstract

A simple method for calculating multi-component gas-solid equilibrium phase diagrams for chemical vapor deposition (CVD) systems is presented. The method proceeds in three steps: dtermination of stable solid assemblages, evaluation of gas-solid stability relations, and calcuation of conventional phase diagrams using a new free energy minimization technique. The phase diagrams can be used to determine (1) bulk compositions and phase fields accessible by CVD techniques; (2) expected condensed phases for various starting gas mixtures; and (3) maximum equilibrium yields for specific CVD process variables. The three step thermodynamic method is used to calcuate phase diagrams for the example CVD system Ti-B-Cl-H at 1200 and 800/sup 0/K. Examples of applications of the diagrams for yield optimization and experimental accessibility studies are presented and discussed. Experimental verification of the TiB/sub 2/ + Gas/Gas phase field boundary at 1200/sup 0/K, H/Cl = 1 confirms the calculated boundary and indicates that equilibrium is nearly and rapidly approached under laboratory conditions.