Spatial Distribution of Strain and Phases in Si Nano-Indentation Analysed by Raman Mapping

摘要

Raman mapping was used to obtain information on strain and phase distribution around Berkovich indentations in a (001) silicon wafer. Strain is obtained through phonon shift while metastable phases of silicon are identified by their signatures at respective wavenumbers. Raman line mapping across several indentations, characterized by various maximum loads and loading rates, allowed determination of both the strain in the cubic diamond structure of silicon (cd or the Si-Ⅰ phase) and the spatial distribution of the Si phases produced under contact loading. Crystalline silicon phases (Si-Ⅲ (6c8) and Si-Ⅻ (r8) phases), as well as amorphous material were observed within the indentation contact area. The volume ratio of the two metastable Si phases (bc8 and r8) with respect to cd silicon, deduced from the Raman intensity ratio Ⅰ_(350)/Ⅰ_(520), increased with the maximum load due to a larger size of the transformed area compared to the laser probe size. Asymmetric profile of the Raman shift across the indentation suggests that a steep relaxation of the stress occurs along the direction defined by the two facets, while a gradual behaviour is observed in the direction perpendicular to the facet.