POLYTYPE TRANSITIONS IN ION-IMPLANTED SILICON-CARBIDE

The effects of ion implantation in 6H-SiC have been studied, using layer-by-layer etching in conjunction with RHEED. Samples were implanted with 100 keV Si at doses ranging from 10(13) to 2.5 x 10(15) cm-2, and annealed at temperatures of 1100-2200 K. On the basis of RHEED picture analysis taken from annealed and unannealed crystals, and comparison with calculated depth profiles of impurity distribution and damage profiles, the following conclusions were drawn: In crystals implanted with doses lower than the amorphization dose, microinclusions of twinned 3C-SiC were found in the region of the maximum of each depth profile and between them. In crystals implanted with doses larger than the amorphization dose which were annealed at temperatures leading to formation of polytype 3C-SiC, the 3C-SiC layer was thinner than the amorphized layer. This is due to the reproduction of the substrate structure at the beginning of recrystallisation, accompanied by defect generation which results in the phase transition 6H --> 3C. At annealing temperatures which lead to formation of a polytype of the substrate, microinclusions of 3C-SiC were found in the area of both depth profiles. Under nonisothermal annealing conditions, the polytype structure of the recrystallized layer is determined by the temperature at which the maximum recrystallisation rate occurred. The findings obtained were used to prepare buried layers of polytype 3C in 15R and 6H substrates.