Abstract

Precise, real-time noncontact temperature measurement of semiconductor wafers during processing steps is of critical importance in semiconductor manufacturing. This is particularly true for new processes, such as rapid thermal processing (RTP), which are being developed in response to the reduced thermal budgets associated with extreme submicrometer features. Present noncontact temperature measurement schemes based on pyrometry, infrared transmission, and Raman scattering each suffer from some combination of high cost, measurement complexity, process sensitivity, and insufficient resolution. Recently, we have proposed and demonstrated a technique based on thermal expansion of a grating etched into the Si.¹ A highly precise temperature readout (±0.5°C) is achieved in a projection moire configuration in which the grating on the wafer is referenced to a second grating formed by interference of two laser beams at the wafer surface. Various geometric configurations have been investigated. A major benefit of this technique is that it is insensitive to the inevitable tilt and warpage of the wafer under the extreme thermal conditions of RTP. An optical Fourier transform technique is demonstrated that allows for a direct temperature measurement. Signal processing techniques have been developed both for optimizing the signal-to-noise ratio, and hence the resolution, and for measurement automation.

© 1992 Optical Society of America