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In-situ wafer curvature measurements during rapid thermal annealing of Si(100) wafers

During Rapid Thermal Annealing (RTA) of silicon wafers a nonuniform temperature distribution may exist across the wafer caused by a variation of the radiation flux. Due to the thermal gradient, differences in thermal expansion introduce thermal stresses in the material. In a modified RTA system the deformation originating from the thermal stress was monitored by measurement of the wafer curvature using the reflection of a laser beam off the wafer surface. The measurements were performed in real-time by a dedicated image processing system. Silicon wafers were radiatively heated to approximately equals 850 degree(s)C for 90 seconds by halogen lamps at a constant temperature of approximately equals 1740 degree(s)C. The results show that during the complete RTA cycle wafers are in a deformed state. In particular, the deformation is largest during the heating and cooling transients. It is shown that the deformation is reduced by application of radiation shielding.