Constraints on micro-Raman strain metrology for highly doped strained Si materials

Abstract

Ultra-violet (UV), low penetration depth, micro-Raman spectroscopy and high resolution X-ray diffraction (HRXRD) are utilised as complementary, independent stress characterisation tools for a range of strained Si samples doped by low energy (2 keV) Sb ion implantation. Following dopant implantation good agreement is found between the magnitudes of strain measured by the two techniques. However, following dopant activation by annealing, strain relaxation is detected by HRXRD but not by micro-Raman. This discrepancy mainly arises from an anomalous red shift in the Si Raman peak position originating from the high levels of doping achieved in the samples. This has serious implications for the use of micro-Raman spectroscopy for strain characterisation of highly doped strained Si complementary metal-oxide semiconductor devices and structures therein. We find a direct correlation between the Si Raman shift and peak carrier concentration measured by the differential Hall technique, which indicates that UV micro-Raman may become a useful tool for non-destructive dopant characterisation for ultra-shallow junctions in these Si-based materials.