Evaluation of super-critical thickness strained-Si on insulator (sc-SSOI) substrate

Crystal quality and strain distribution in SOI layer of conventional strained-Si on insulator (SSOI) and super-critical thickness strained-Si on insulator (sc-SSOI) were evaluated by in-plane X-ray diffraction (XRD), Raman spectroscopy, and other techniques. The surface defect distribution measured by wafer inspection system shows pit-type and line defects in both SSOI layers. More specifically, the sc-SSOI material has more line defects than conventional SSOI layers. Cross-hatched pattern defects were observed using X-ray topography (XRT) measurements. Raman mapping of 300 mm wafers shows the strain at the center of the wafer is larger than at the edge. In magnified close-up mapping, cross-hatched contrasts corresponding to misfit dislocations are observed, while the surface morphology is completely smoothed out. In-plane XRD measurements show the strain depth variations are quite uniform along the depth direction. The full width at half maximum (FWHM) of in-plane XRD peaks obtained from strained-Si layers is much larger than for un-strained SOI and bulk Si, reflecting poor crystal quality. SSOI was fabricated by the layer transfer of strained-Si on a virtual SiGe substrate. Therefore, we believe the crystal quality and strain distribution originate in the donor strained Si when virtual SiGe substrate is the starting material.