Positive Charges and E' Centers Formed by Vacuum Ultraviolet Radiation in SiO2 Grown on Si

Silicon dioxide films thermally grown on Si are irradiated with vacuum ultravioulet (VUV) photons (16.7 and 16.8 eV) as the films are supplied with bias voltages between -10 and 10 V. The resultant positive charges and E' centers in the films are studied by C-V (capacitance-voltage) and ESR measurements, respectively. The observed E' centers are distributed near the SiO2 surface, while the positive charges are localized at or very near the SiO2/Si interface. The positive charges and the E' centers show different characteristics in their bias and irradiation time dipendencies as well as in their depth distributions. These results indicate that the detected positive charges are different from holes trapped at oxygen vacancy sites between weak Si–Si bonds.