Layer morphology and Al implant profiles after annealing of supersaturated, single crystalline, amorphous and nanocrystalline SiC

Al supersaturated SiC layers (5x10^20 Al cm-3) were produced by multi-energy, high dose ion implantation into 6H- and 4H-SiC. Several implantation schemes with varying implantation sequence and temperature were investigated. In dependence on the implantation conditions damaged single-crystalline, amorphous or nanocrystalline layers were formed. The layer morphology and Al distribution in the as-implanted state as well as structural changes and related Al redistribution after high temperature annealing (1500-1700°C) were characterized by XTEM, RBS/C, AFM and SIMS analysis. Remarkable Al redistribution effects have been found after annealing of Al supersaturated SiC. During high temperature annealing Al atoms in excess to the solid solubility (2x1020 Al cm-3) tend to precipitate in single crystalline SiC whereas they diffuse out in amorphous or nanocrystalline SiC. Redistribution of Al with concentration below the solid solubility is governed by transient enhanced diffusion which can be controlled by the annealing scheme. Amorphization of SiC is advantageous in the case of Al doping to levels higher than the solid solubility because it prevents Al precipitation during annealing and helps to form box-like Al profiles with smooth plateau and abrupt edge.