Non-destructive characterisation of doped Si and SiGe epilayers using FTIR spectroscopic ellipsometry (FTIR-SE)

FTIR-SE has been used to determine, non-destructively, carrier density (n, p) and thickness (t) of Si and SiGe epitaxial layers. The FTIR-SE measurements were made using a SOPRA GES5-FTIR instrument, operating over the range 600–4000 cm−1. A range of samples has been studied, including undoped and doped Si epilayers with t ≈1–17 μm, p ≈7×1017–1.5×1019 cm−3 and doped Si0.9Ge0.1 epilayers with t ≈50–100 nm, p ≈1–3×1019 cm−3. The results were compared with SIMS and four-point probe measurements. For the Si epilayers, excellent agreement was obtained for thickness values and best agreement for carrier density values was obtained using m*=0.26 me in the Drude free-carrier analysis. Carrier density of thin SiGe layers has been measured by FTIR-SE for the first time. A novel layer structure was used to improve sensitivity in the available spectral range. Lower limits of sensitivity to thickness and doping level have been established. Both thickness and carrier density were determined with good precision for 100 nm layers.