Mixed Convection in a Large Area Atmospheric Pressure CVD Reactor

This paper investigates a new CVD reactor geometry to deposit uniform films on large area substrates at atmospheric pressure. The reactor employs a stagnation flow geometry with an impinging central jet. The substrate is also rotated in order to get film uniformity. Calculations have been performed for a wide range of parameters to investigate the effects of inlet flow rates, substrate rotation, and height of the reactor chamber. It is seen that for some combinations of the parameters the flow above the wafer is unsteady. The unsteadiness of the flow is subsequent to the sharp turning at the conclusion of the inlet nozzle. The sudden expansion makes the shear layer unsteady much in the same way as the flow in a sudden expansion. Thus, the effect of rounded corners on damping such instabilities of the shear layers is explored. By employing the rounded corners, we have been able to reduce the RMS non-uniformity to about 1% at atmospheric pressure on 30 cm wafer. The impinging jet geometry can therefore be used for the deposition of many thin solid films without the penalty of a vacuum system and associated equipment costs.