OPTICAL-TEMPERATURE MEASUREMENT BY GRATING EXPANSION FOR ROTATING SEMICONDUCTOR WAFERS

A noncontact temperature measurement technique, diffraction-order anal ysis, based on monitoring the change in diffraction angle from a grati ng as a result of thermal expansion, is described and results for both Si and GaAs are presented. Two incident beams are used to provide a d ifferential measurement, independent of wafer tilt. Image processing t echniques are used to calculate the relative temperature in near real time from the optical signals. Good agreement between optical and the thermocouple temperature measurements is obtained, with an accuracy an d precision of +/-0.3 degrees C demonstrated over a 20-600 degrees C t emperature range for a GaAs sample. Analysis of the effects of all six rigid-body motions of the wafer on the measurement is presented. The measurement is independent of all translational motions; rotational mo tions (pitch, roll, and yaw) can all be monitored with the same measur ement scheme and the temperature measurement corrected for their effec ts. In many applications in semiconductor manufacturing, wafers are ro tated to ensure uniformity. The diffraction-order analysis technique i s demonstrated for a rotating wafer with a 3 sigma precision of 1.95 d egrees C. (C) 1996 American Vacuum Society.