Thermal stability of metastable silicon phases produced by nanoindentation

Raman spectroscopy and transmission electron microscopy are used to investigate the temperature effects on the stability of metastable silicon phases (Si–III and Si–XII) produced by nanoindentation. It is found that the thickness of the specimen beneath the residual imprint plays an important role in the phase transformation sequence during heating up to 200 °C. Amorphization is preferred in nanoindents located in thin and loosely constrained areas; formation of Si–IV from Si–III/Si–XII is observed in the residual imprints located in the areas with an intermediate thickness; and the formation of an unidentified “Si–XIII” structure, which precedes the formation of Si–IV, is observed in nanoindents constrained by the bulk wafer. The phase transformation sequence in the indented samples under annealing is established as follows: Si–XII→Si–III→Si–XIII (thick sample only)→a-Si or Si–IV→nanocrystalline Si–I→Si–I.