STUDY ON EXCIMER-LASER INDUCED DEFECTS IN SIO2-FILMS ON SI BY VARIABLE-ENERGY POSITRON-ANNIHILATION SPECTROSCOPY

Using variable-energy positron annihilation spectroscopy, we have inve stigated the defects induced by ArF excimer laser (6.4 eV) irradiation of SiO2 films (500 nm thick) on Si(100). Films of both thermally grow n oxide, and plasma enhanced chemical vapor deposited oxide were studi ed. It is proposed that E' centers (=Si.), nonbridging oxygen hole cen ters (NBOHC, =Si-O.) and their charge transfer states may trap positro ns and affect the positronium annihilation modes. For the thermally gr own oxide, the content of E' centers, and hence original structural de fects such as oxygen vacancies (=Si-Si=) at the SiO2/Si interface, is much higher than that in the SiO2 film itself. For SiO2 films deposite d 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 th e radiation-induced defects. The NBOHC formed strongly trap positrons and decrease the positronium formation fraction. The annealing behavio r of the radiation-induced defects in both samples is characteristic o f the original structural defects.