Microstructure of silicon-on-insulator structures produced by high dose nitrogen implantation of silicon

Abstract (100) silicon wafers have been implanted with 200 keV N + ions to doses ranging from 0.25 to 1.4×10 18 cm −2 , at a temperature of 500±10° C . The microstructure in the as-implanted state and after annealing at 1200°C for 2 h was investigated by TEM. In the unannealed sample implanted to a dose of 0.25×10 18 cm −2 , cross-sectional TEM indicated an amorphous layer close to the peak of the nitrogen distribution as shown by SIMS. Damaged silicon layers were present above and below the amorphous layer. A dose of 1.4×10 18 cm −2 produced a thicker amorphous region containing bubbles. Annealed samples, implanted with doses of 1.0 and 1.4×10 18 cm −2 were examined and compared with earlier observations at doses of 0.25 and 0.75×10 18 cm −2 . A dose of 1.0×10 18 cm −2 produced a well defined α-Si 3 N 4 layer showing a sub-layer structure, and containing small silicon islands. A dose of 1.4×10 18 cm −2 gave a more complex layer structure, including α-Si 3 N 4 free from silicon islands, and bubbles. Some threading dislocations (∼10 8 –10 9 cm −2 ) were present in the silicon overlayer.