Large area, uniform silicon-on-insulator using a buried layer of oxidized porous silicon

We describe a process for the formation of silicon-on-insulator structures by selective anodization of a buried p-type layer to form porous silicon which is then oxidized. A buried n-type layer ensures that the flow of the anodizing current, and hence the formation of the porous silicon layer, is directed laterally rather than downwards. By this means we have produced defect-free, 200-nm-thick and 40-μm-wide silicon strips extending across the full width of device wafers and resting on 800 nm of silicon dioxide. This approach, which shows considerable promise for further enhancement, gives continuous large areas of high quality isolated silicon with minimal wafer warpage compared with most existing silicon-on-silicon dioxide technologies.