Spatial temperature distribution in semiconductor wafers during rapid thermal processing is obtained by means of acoustic tomography. Ultrasonic Lamb waves are excited in the wafer by acoustic transducers bonded to spring‐loaded quartz support pins located at the wafer periphery. The Lamb wave time of flight in the wafer is used to measure the average wafer temperature with ±0.5 °C accuracy for a S/N ratio exceeding 55 dB. Spatial temperature information is gathered by electronic switching of the transmitter and receiver transducers. Tomographic reconstruction techniques are then used to calculate the temperature distribution from the measurements with different pixel maps. Using eight transducers, the thermal image of a 10 cm, (100) silicon wafer is obtained with 2×2 cm2 pixel resolution. Thermal image rates of 2 images/s are achieved by the system enabling real‐time control of wafer temperature distribution during rapid thermal processing.
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