Numerical simulation of chemical vapor deposition processes under variableand constant property approximations

The chemical vapor deposition (CVD) process for silicon, using silane (SiH4 ) with hydrogen (H-2) as the carrier gas, is modeled numerically using cons tant properties evaluated at various reference temperatures T-r e f . Resul ts are compared with those from a numerical model based on variable transpo rt properties. When the susceptor is isothermally heated, deposition rates predicted by the simplified model agree very well (5% error) with the varia ble property solution. A susceptor heated by means of a uniform heat flux i nput has a large temperature variation across the susceptor surface, yieldi ng considerable error from the constant property model. However, a carefull y chosen T-r (e f) for cases with large heat flux input, which gives rise t o diffusion-controlled deposition (surface Damkohler number D alpha(S) much greater than 1) is able to capture property variation effects and predict the deposition rate with reasonable accuracy. A variable property model is necessary at low heating rates, since reaction-controlled deposition (D alp ha(S) much less than 1) has a strong dependence arising from exponential te mperature dependence of the chemical reactions and the properties. The stud y shows that the constant property model may be used to obtain solutions wi th satisfactory accuracy for a variety of operating conditions. The results and observations may be used as guidelines for future CVD reactor design a nd choice of appropriate operating conditions.