Oxygen out-diffusion from buried layers in SOI and SiC–SOI substrates

We have made a comparative study of the oxygen out-diffusion process during heat treatment of SOI wafers and SiC–SOI hybrid substrates. SOI materials with three different thicknesses (2, 20 and 410 nm) of buried oxide (BOX) were used in the investigation. High-resolution cross-sectional transmission electron microscopy (HRXTEM) together with laser interferometry was used to determine the remaining thickness of the BOX-layer after heat treatment. After complete removal of the BOX-layer of SOI wafers, the Si/Si interface appears to be sharp and defect-free. Similar results were obtained for SiC–SOI hybrid substrates after removal of the entire buried oxide layer. For all combinations investigated oxide removal was accompanied by a thickness reduction and roughening of the silicon surface layer as verified by atomic force microscopy (AFM).