Photoluminescence evaluation of light element impurities in ultrathin SOI wafers by luminescence activation using electron irradiation

Light element impurities in ultrathin silicon-on-insulator (SOI) wafers were characterized by photoluminescence (PL) spectroscopy under ultraviolet (UV) light excitation. Various commercial SOI wafers were irradiated by 1 MeV electrons with a fluence of 3 × 1016–1 × 1017 cm−2. The electron irradiation induces point defects, which react with light element impurities, resulting in the formation of strong radiative centers. We were able to successfully observe the C-line originating from the complex between interstitial carbon and oxygen in all the samples and also the G-line from the complex between interstitial and substitutional carbon in some of them. This demonstrates the presence of carbon and oxygen impurities in an ultrathin top Si layer with a thickness down to 62 nm. We investigated the difference in the impurity concentration depending on the wafer fabrication methods and the variation of impurity concentration in the respective wafers.