Quantitative analysis of carbon impurity concentration in silicon epitaxial layers by luminescence activation using carbon ion implantation and electron irradiation

The calibration curve for the carbon concentration in silicon epitaxial layers was obtained by photo-luminescence spectroscopy after carbon ion implantation and electron irradiation. Low carbon concentrations on the order of 1014 atoms/cm3 affected properties such as the on-resistance and carrier lifetime of insulated gate bipolar transistors (IGBTs). We focused on carbon impurities because interstitial carbon can form complexes, such as complexes of interstitial and substitutional carbon (Ci-Cs) and of interstitial carbon and oxygen (Ci-Oi), which produce deep levels in the energy band gap. To verify the effects of carbon impurities separately from those of oxygen impurities, oxygen-free silicon epitaxial layers were studied. The carbon concentration in silicon epitaxial wafers was evaluated quantitatively by using our calibration curve. Carbon ion implantation and photoluminescence spectrum measurements were performed to obtain the slope of the calibration curve. In addition, secondary ion mass spectrometry measurement gave absolute carbon concentration against photo-luminescence intensity for fixing the calibration curve. The calibration curve was used to determine the carbon concentration for each IGBT. Carbon impurity concentrations as low as 1014 atoms/cm3 in silicon epitaxial layers lowered device performance. Therefore, decreasing the carbon impurity concentration is essential for improving the performance of advanced IGBTs. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)