SOI material characterization using optical second harmonic generation

While SOI wafer manufacturing processes such as SIMOX and BESOI have been developed, it remains a challenge to produce SOI wafers with extremely thin top silicon layers that are uniform in thickness, low in defects, high in crystalline quality, and compatible to bulk silicon in electrical performance. These stringent requirements on SOI wafers have stimulated a parallel effort to develop characterization techniques for starting SOI wafer qualification, as conventional characterization techniques often prove to be inadequate as a result of complications arising from the presence of the buried oxide layer in SOI. New methods therefore have emerged to answer the needs. Here we report the use of optical second harmonic generation (SHG) method for the characterization of SOI wafer quality. This technique is non-destructive, real time, very sensitive and versatile. It can be used to address a number of SOI wafer issues such as silicon film uniformity, wafer bonding induced mechanical stress, dopant and defect density in the thin film, and buried oxide layer interfacial quality. Applying this method to the investigation of BESOI and SIMOX wafers, we have observed distinctive SHG signals and signal changes as the wafers are subjected to different processing conditions. These results indicate that the quality of the SOI wafers can in fact be probed effectively using the SHG technique.