Study of buoyancy-induced flows in a prototypical CVD reactor

Numerical simulations of flow, temperature and concentration fields are used to understand the effects of operating parameters on flow pattern, and film growth in vertical rotating-disk chemical vapor deposition (CVD) reactors. A study was first undertaken to understand the effects of various parameters on the flow and concentration fields in a prototypical CVD reactor, which has been constructed in a laboratory. The growth characteristics of the prototypical reactor in terms of operating pressure, flow rate, substrate rotation rate, and the diameter of precursor gas supply are predicted. While these results are similar to what have been previously reported, the present study reaffirms current understanding of CVD flow physics and led to explorations in new operating and geometrical conditions that can improve quality and growth rate of the films.; Based on the study of the prototypical CVD reactor, a new design is proposed. The performance of the new stagnation flow CVD reactor at pressures close to atmospheric pressure is numerically explored. This reactor has a low height with inflow from the top through a central nozzle. The annular wall above the substrate is maintained at a low temperature to avoid deposition on this surface. The substrate is also rotated to improve the hydrodynamic patterns and provide azimuthal symmetry. Results of a number of high-resolution calculations indicate that this reactor can be operated at sub-atmospheric and atmospheric pressures. It is also shown that the growth rate is significantly large, in addition to a high degree of film uniformity.; Next, an understanding the influence of the transient operating conditions in the prototypical CVD reactor was sought. Film growth rate shows time varying pattern due to the transient operating conditions. But it oscillates between two end steady states. Thus, it is observed that film growth rate and uniformity cannot be improved by applying pulse sequence of precursor gas, pulse sequence of inlet mass flow rate, and time-varying rotation speed of the wafer.