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

Abstract: Quantification of Ge in Si1-xGex structures (0.092<x\<0.78) was carried 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 intensity ratios of GeCs2+/SiCs2+ and 74Ge-/30Si- secondary ions and post-ionized 70Ge+/28Si+ sputtered neutrals with Ge concentration was obtained. The calibration data were used for quantitative depth profiling of [10x(12.3 nm Si0.63Ge0.37/34 nm Si)] structures on Si. Satisfactory compliance of the quantified Ge concentration in SiGe layers with the data measured by high-resolution X-ray diffraction was obtained for both techniques. Both SIMS and SNMS experimental profiles were fitted using the Hofmann mixing-roughness-information depth (MRI) model. In case of TOF-SIMS the quality of the reconstruction was higher than for SNMS since not only the progressing roughening, but also crater effect and other processes unaccounted in the MRI simulation could have significant impact on plasma sputter depth profiling.