Quantification of carbon in Si_1-x-yGe_xC_y with uniform profiles

Methods to quantify the carbon concentration of CVD grown Si_1-x-yGe_xC_y (0.25 < x < 0.37 and 0.01 < y < 0.12) layers on (100) Si with uniform composition profiles were investigated. Two analysis techniques were used: Rutherford backscattering spectrometry (RBS) using a 4.295 MeV He⁺² incident ion and elastic recoil detection (ERD) using a 24 MeV Si⁺⁵ incident ion. For the RBS measurements the ¹²C(α,α)¹²C elastic resonance reaction near 4.265 MeV was used to enhance the scattering cross section of carbon. These carbon concentrations were calculated by either integrating the resonant scattering cross section across the energy width of the layer or by using a Lorentzian fit to estimate the area. The backscattering data were additionally analyzed with the program RUMP. These different analysis techniques resulted in a large scatter in the RBS predictions for the carbon concentrations depending on how the resonant cross sectional area was calculated. The appropriateness of each technique was judged by comparing the predicted concentrations to those obtained by ERD. The divergence between the carbon concentration predicted by using the Lorentzian approximation and the ERD values was great enough to deem this method as inappropriate. The values obtained by RUMP were systematically greater than the ERD concentrations, however the percent difference was never more than 20. The predicted carbon concentration that had the closest correlation to ERD was found by integrating an appropriate scattering cross section across the energy width of the layer.