Study on excimer laser induced defects in SiO2 films on Si by variable-energy positron annihilation spectroscopy

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Abstract
Using variable‐energy positron annihilation spectroscopy, we have investigated the defects induced by ArF excimer laser (6.4 eV) irradiation of SiO2 films (500 nm thick) on Si(100). Films of both thermally grown oxide, and plasma enhanced chemical vapor deposited oxide were studied. It is proposed that E’ centers (≡Si⋅), nonbridging oxygen hole centers (NBOHC, ≡Si‐O⋅) and their charge transfer states may trap positrons and affect the positronium annihilation modes. For the thermally grown oxide, the content of E’ centers, and hence original structural defects such as oxygen vacancies (≡Si‐Si≡) at the SiO2/Si interface, is much higher than that in the SiO2 film itself. For SiO2 films deposited on Si by plasma‐enhanced chemical vapor deposition, the impurity of ≡Si‐OH (1.2 wt %) throughout the oxide layer acts as a precursor to the radiation‐induced defects. The NBOHC formed strongly trap positrons and decrease the positronium formation fraction. The annealing behavior of the radiation‐induced defects in both samples is characteristic of the original structural defects.