FLOW AND HEAT-TRANSFER IN CVD REACTORS - COMPARISON OF RAMAN TEMPERATURE-MEASUREMENTS AND FINITE-ELEMENT MODEL PREDICTIONS

A combined experimental and modelling study of flow and heat transfer in a horizontal chemical vapor deposition (CVD) reactor is described. Effects of manipulation of standard CVD operating conditions (flow rate, pressure, and carrier gas) on flow and heat transfer characteristics are considered along with changes in susceptor tilt angle and orientation of the reactor relative to the direction of gravity. Gas phase temperatures are measured by spontaneous Raman scattering and smoke trace experiments are used to visualize flow structures. Excellent agreement is obtained between measured temperatures and those predicted by a finite element analysis of a two-dimensional model. The observed flow structures, including recirculation cells and qualitative changes with reactor orientation are also reproduced by the model. In particular, the results show a reversal of the fluid motion in recirculation cells when the susceptor is placed on the top reactor wall rather than on the bottom. The temperature measurements demonstrate that high flow rates and replacement of H2 by N2 as a carrier gas lead to the formation of steep thermal gradients adjacent to the susceptor and development of a "cold finger" of gas that may be advantageous in obtaining uniform deposition rates. Furthermore, the importance of accurate heat transfer modelling of CVD reactor walls is emphasized. © 1990.