Rapid identification of ultrathin amorphous damage on monocrystalline silicon surface
Amorphous silicon (a-Si) remains a common surface damage during ultra-precision machining of monocrystalline Si. However, it was difficult to identify the amorphous damage with several nanometers by traditional detection methods, which hinders severely performance improvement of Si-based products. In this study, ultrathin a-Si was found to act as a mask against etching in HF/HNO3 mixtures, resulting in forming protrusive hillocks. Reciprocating sliding on an atomic force microscope (AFM) was employed for simulating material removal event in surface manufacturing. Effects of normal load, etching time and etchant concentration on selective etching were investigated to optimize parameters for amorphous damage detection. The mechanism for the selective etching were further addressed based on high-resolution transmission electron microscope (HRTEM) detection, as well as comparative etching of surface structures with different crystal damages or Si oxide. Further analysis demonstrated that lower dangling bond density of a-Si can result in the reduction of dissolution rate, while deformed Si lattices, including stacking faults, dislocations and microcracks, can facilitate rapid selective etching. By the proposed selective etching, ultrathin amorphous damage and its spatial distributions can be identified rapidly with high resolution and low destruction. This study sheds a new light on achieving high-quality Si surface in ultra-precision machining.