Direct observation of gate oxide destruction due to BOX breakdown in SOI

Gate oxide integrity (GOI) of silicon-on-insulator (SOI) wafers is, in most cases, inferior to that of bulk Si wafers. GOI degradation mechanisms related to BOX breakdown have been studied in previous works (Adan et al., 1998; Iwamatsu et al., 1997), where an equivalent circuit model or responsibility of pre-existing BOX defects have been reported. In this work, we observed leakage spots of gate oxide and BOX using optical beam induced current (OBIC) and cross-sectional TEM. As a result, we found that gate oxide is broken at the same location as BOX leakage spots, and degradation of gate oxide integrity is caused by mechanical damage associated with deformation of BOX rather than electrical damage.