Defect-free removal of monocrystalline germanium

Germanium (Ge) serves as an emerging alternative for smaller devices with dense features and is of significance in microelectronics industry. Since surface defects can degrade directly the performances of Ge-based devices, it is essential to reduce or eliminate machining damage on Ge substrate. In this study, defect-free material removal behaviors of Ge were investigated by a series of nanoprocessing with SiO2 and Al2O3 tips using an atomic force microscope (AFM), and the tests by diamond tip was 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 most 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 Ge surface during the material removal process by SiO2 and Al2O3 tips. It also demonstrates that defect-free material removal occurred on 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 defect-free removal behavior by SiO2 or Al2O3 tip sliding. This study may shed light on mechanochemical removal mechanism and provide the guidance for defect-free processing of Ge.