Detection of impurities on silicon surfaces

Impurities initially present on a Si surface can be detected using the photo I-V technique. An Al impurity deposited to a thickness less than 8 Å on a silicon substrate which was subsequently oxidized, capped by a chemically vapor deposited (CVD) SiO2 layer, and incorporated into a capacitor structure with an Al gate electrode was found mostly near the interface between the thermal and CVD oxides using the photo I-V technique. This impurity layer which was probably converted to Al2O3 showed greatly enhanced electron trapping compared to either oxide layer.