Quantitative depth profiling of Si1–xGex structures by time-of-flight secondary ion mass spectrometry and secondary neutral mass spectrometry

Quantification of Ge in Si1–xGex structures (0.092 ≤ x ≤ 0.78) was carried out by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and electron-gas secondary neutral mass spectrometry (SNMS). A good linear correlation (R2 > 0.9997) of the intensity ratios of secondary ions GeCs2+/SiCs2+ and 74Ge−/30Si− and post-ionized sputtered neutrals 70Ge+/28Si+ with Ge concentration was obtained. The calibration data were used for quantitative depth profiling of [10 × (12.3 nm Si0.63Ge0.37/34 nm Si)] structures on Si. Satisfactory compliance of the quantified Ge concentration in SiGe layers with the values obtained by high-resolution X-ray diffraction was revealed for both techniques. SIMS and SNMS experimental profiles were fitted using Hofmann's mixing-roughness-information depth (MRI) model. In the case of TOF-SIMS, the quality of the reconstruction was better than for SNMS since not only the progressing roughening, but also the crater effect and other processes unaccounted in the MRI simulation could have a significant impact on plasma sputter depth profiling.