Quantification of substitutional and interstitial carbon in thin SiGeC films using in-line X-ray-photoelectron spectroscopy

One of the most important questions concerning the epitaxial growth of Si1-yCy or Si1-x-yGexCy is the ratio of carbon incorporated into substitutional and interstitial sites, which is highly dependent on growth conditions. Usually, the quantification of the total (C-tot), the substitutional (C-sub) and the interstitial (C-int) carbon concentrations is achieved using a combination of secondary-ion mass spectrometry and X-ray-diffraction, based on careful calibration and appropriate preparation. In this study, we demonstrate the potential of non-destructive, in-line X-ray photoelectron spectroscopy to obtain the quantification of both C-sub and C-int in a single measurement. For substitutional carbon atoms, the XPS C 1s signal intensity increases proportionally with the carbon content, with a characteristic peak at 284.00 eV. When carbon is incorporated into interstitial sites, a shift of the C 1s peak towards lower binding energies is detected. Moreover, a broadening of the peak is observed, due to the appearance of a characteristic peak at 283.30 eV. Here, we describe the development of a measurement procedure and provide a critical discussion on the possible sources of error. Finally, an excellent correlation between the newly developed XPS quantification and the standard XRD/SIMS method is demonstrated.