Thermal Stress Analysis for Rapid Thermal Process With Convective Cooling

Abstract

A fast temperature ramp of rapid thermal processing (RTP) with convective cooling used to shorten the cooling time for the wafer is presented in this paper. Based on thermal and stress analyses, the behavior of the highly coupled physics in RTP, such as radiative heat transfer, transient flow, and thermal stress is studied in detail. From simulation results of the flow field, a large recirculation cell between the wafer edge and the chamber wall is predicted and the effect of buoyancy on the behavior of the flow field is examined. Since the buoyancy-induced recirculation aggregates thermal nonuniformity due to edge effect, a guard ring is then suggested to be placed at the edge of the wafer to reduce the heat loss from the wafer edge and reflect the radiative energy back into the wafer during the cooling process. Furthermore, a large inlet gas mass flow rate is found to suppress the recirculation and shorten the cooling time. However, a fast convective cooling rate would result in a significant temperature difference between center and edge of the wafer, thus causing material failure due to an increase of thermal stresses.