Optical strain measurement in ultrathin sSOI wafer

摘要

Three optical characterizations, Raman spectroscopy (RS), low temperature photoluminescence (LTPL) and photoreflectance (PR) have been used for strain characterization in thin (15 nm) strained silicon on insulator (sSOI) layer. The RS using visible and UV excitation allows to determine the strain in the thin overlayer and a value of 1% has been deduced from the LO phonon energy shift. The LTPL spectra analysis shows a bandgap shrinkage at Δ point of 140 meV. This is due to the Δ_6 conduction band splitting and leads to a strain value of 1%. Finally from PR measurements a bandgap shrinkage at Γ point of 0.19 eV and 0.08 eV for light holes and heavy holes respectively has been measured, thus confirming the 1% strain value obtained by Raman spectroscopy and LTPL measurements.