Defect-free removal of monocrystalline germanium

Germanium (Ge) serves as an emerging alternative for smaller devices with dense features and is of significance in the microelectronics industry. Since surface defects can degrade directly the performance of Ge-based devices, it is essential to reduce or eliminate machining damage on Ge substrate. In this study, the defect-free material removal behaviors of Ge were investigated by a series of nanoprocessing with SiO₂ and Al₂O₃ tips using atomic force microscope (AFM), and the tests with a diamond tip were performed for comparison. Material removal on Ge surface exhibited the dependence on ambient humidity whatever SiO₂, Al₂O₃ or diamond tip was employed, while the sliding with Al₂O₃ tip can lead to the largest quantity of surface removal. Combined with micro-Raman spectra and high-resolution transmission electron microscopy (HRTEM) detection of the worn area, it was confirmed that no defects existed on the Ge surface during the material removal process by SiO₂ and Al₂O₃ tips. It also demonstrates that defect-free material removal occurred on the Ge surface under contact pressures far below the yield strength of Ge, which can be attributed to water-participated mechanochemical reactions. Further analysis showed that the presence of hydroxyl ions and radicals weakening Ge-Ge backbone bonds could dominate the defect-free removal behavior by SiO₂ or Al₂O₃ tip sliding. This study may shed light on the mechanochemical removal mechanism and provide the guidance for defect-free processing of Ge.