Applied RTP optical modeling: an argument for model-based control

A simulation of a complete rapid thermal processing (RTP) system is made to investigate the accuracy of various techniques for temperature control. The process simulated was the chemical vapor deposition (CVD) of polycrystalline silicon over an oxide. Control strategies considered were, open loop control, pyrometer control, pyrometer control with a correction for emissivity changes produced by CVD, and open loop control with the lamp heating programmed as a function of time, based an model predictions. The temperature variation and final film thickness of each was predicted by the simulation. The results indicate that model-based open loop control is viable strategy for practical RTCVD control. Based on this strategy, model-based open loop control was then implemented for the control of an existing RTP system. The experimental results confirm the simulations and provide improved temperature control for RTCVD