Thermoluminescence and color centers in rf-sputtered SiO2 films
Abstract
Thermoluminescent (TL) glow curves of rf-sputtered SiO2 films deposited on silicon have been measured and correlated with optical absorption of the films. As-sputtered SiO2 films are thermoluminescent without further exposure to exciting radiation. Films with a strong optical-absorption band at 7.6 eV (E band) give first-order glow curves. They have a TL center with energy ∼ 0.66 eV and a low-frequency factor s ∼ 104 sec -1, which suggests that trapping centers and recombination centers are physically separated. Irradiation of sputtered SiO2 films with x rays produces complex TL glow curves which have been analyzed by thermal cleaning techniques. Trapping centers with energies of 0.66, 0.84, and 1.04 eV are found. The complexity of TL glow curves in sputtered SiO2 films after x-ray irradiation arises primarily from variations in s, rather than from a broad spectrum of trapping energies. The effect on TL glow curves of annealing SiO2 films in oxygen and forming gas has been studied. When samples with a strong E band are annealed in O2, a decrease in absorption coefficient at 7.6 eV is paralleled by an increase in TL intensity. A trapping center with E ∼ 1.40 eV is produced by annealing of the E band followed by x-ray irradiation. A hyperbolic heating rate 1/T=1/T0 - at, used for all TL measurements, simplified analysis of TL glow curves. © 1972 The American Institute of Physics.