Deformation Mechanisms of Semiconductor Materials under Nanoscratching and Nanogrinding

Semiconductor wafer machining that enables the wafers to be used practically must achieve a damage-free subsurface. This requires a comprehensive understanding of the fundamental mechanisms of deformation of the semiconductor materials involved in the machining processes. In this thesis, the deformations of monocrystalline Silicon (Si) under nanoscratching and nanogrinding were systematically investigated. The experimental results demonstrated that lateral force in nanoscratching/nanogrinding played a key role in the amorphization and the phase transformation of Si. Those results were compared with the well-documented deformation mechanisms induced by nanoindentation. Subsurface crystalline defects, such as stacking faults, dislocations, and twins were observed in the scratched/ground Si samples. The existence of high pressure phases embedded in amorphous Si was discovered when a relatively high load was used in nanoscratching or when large diamond grit sizes were employed during nanogrinding. No cracks were observed under the experimental conditions used. The formation sequence of the deformations was determined. The deformations of monocrystalline gallium arsenide (GaAs) under nanoscratching and nanogrinding were also thoroughly studied. It was found that no amorphization occurred. Twins, dislocations, and cracks were found to be the main deformation mechanisms involved in nanoscratching and nanogrinding of GaAs. An extraordinary phenomenon, i.e. lattice bending, was observed when the scratching/grinding pressure was sufficiently high. Residual stress was suggested to be responsible for this lattice bending. By comparing the nanoscratching/nanogrinding-induced deformations of Si and GaAs, it was noted that amorphization was always the first-induced deformation for Si, whereas no amorphization was observed in the scratched or ground GaAs. This raised a question: what were the mechanisms responsible for the different deformations in those two semiconductor materials? To answer this question, the theory of stacking fault energy was employed. Consequently, the deformation mechanisms of semiconductor materials were related to their intrinsic properties. It was proposed that amorphization was less likely to occur in a semiconductor material with relatively low stacking fault energy. To verify this hypothesis, cadmium zinc telluride (CdZnTe, CZT – with a very low stacking fault energy) was investigated under nanoscratching and nanogrinding. No amorphization was observed in the scratched or ground CZT samples, which was in excellent agreement with the hypothesis