We evaluate the electrical properties of the silicon-on-insulator (SOI) layer made by the wafer bonding using a noncontact laser beam induced conductivity/current (LBIC) method. Since the thickness of the SOl layer used in this study is about 40μm, the He-Ne laser, whose penetration depth for Si is small (about 3μm), is used as the carrier-injection light source.
We use the SOI wafer with some voids which are revealed by the X-ray topography. We have reported that the LBIC signal intensity decreases in the void region. In this study, we measure the microscopic signal variation near the edge of the void. It is observed that the LBIC signal intensity decreases in the outside region within a distance of about 700μm from the void edge. The diffusion length of the injected carrier (100-150μm) is shorter than the width of the region where the signal intensity decreases. Thus the decrease is not due to the carrier diffusion to the void. These results show that the formation of the void degrades the electrical properties not only in the void region but also outside the void.