Significance of Vapor Phase Chemical Reactions on CVD Rates Predicted by Chemically Frozen and Local Thermochemical Equilibrium Boundary Layer Theories

Abstract

Two theories based on (i) chemically frozen (CF), and (ii) local thermochemical equilibrium (LTCE) boundary layers have been developed to predict mass transport (CVD) rates. The theories consider laminar convective‐diffusion boundary layers at high Reynolds numbers, use LTCE boundary conditions (no interfacial kinetic barriers) and include thermal (Soret) diffusion and variable property effects. A method of determining the significance of vapor phase reaction kinetics on deposition rates is provided by comparing these two extreme limits of hoomogeneous chemistry. deposition is studied as an example case, and it is determined that gas phase reactions have no important role on deposition rates and deposition onset conditions. Excellent agreement is obtained between the results of deposition experiments and the predictions of the theories. The implications of the predictions of the two extreme theories to other CVD systems are discussed in detail. It is recommended that in the absence of surface kinetic barriers computationally more efficient schemes paying the greatest practical dividends by providing in‐depth understanding and insight, such as the ones presented here, should precede the detailed “multiparameter” modeling of mass transport phenomena coupled with finite‐rate homogeneous chemistry.