Stabilization of the 3C-SiC/SOI system by an intermediate silicon nitride layer

The material system 3C–SiC on SOI (silicon on insulator) offers outstanding possibilities for high temperature applications. In order to fully benefit from these possibilities, the quality of especially the SOI substrate must be maintained throughout all process steps of device fabrication. This work demonstrates the stabilizing effect of a 6 nm thin silicon nitride layer at the interface silicon overlayer/buried oxide layer (SOL/BOX) of a UNIBOND–SOI substrate. This layer was formed by implantation of nitrogen into a SOI substrate and subsequent annealing for 2 h at 1100°C. The improved stability of the SOI system during SiC deposition is explained by the following fact: the wetting angle of silicon at the melting point is decreased from 87° (Si on SiO2) to 25° (Si on Si3N4). The improved wetting behavior decreases the tendency of silicon to redistribute and to form cavities. A 2.6 μm thick layer of cubic SiC was deposited at 1200°C on a UNIBOND SOI substrate. This sample was only partly implanted with nitrogen. At the non-implanted part, a significant redistribution of the SOL occurred and cavities were extended from the SOL deep into the BOX. Whereas at the N-implanted part, the BOX was completely protected by the silicon nitride layer and only small cavities were extended into the SOL (thicknesses of SOL and BOX were about 150 and 400 nm, respectively). The crystal quality of the SiC layer was almost the same in both cases. Furthermore, the results indicate that an optimization of the whole process will even lead to better results.