Defect centers in oxygen-deficient rf-sputtered SiO2 films. I. Electron spin resonance

Abstract

Two new defect centers have been observed by electron spin resonance (ESR) in rf‐sputtered SiO₂ films with low metallic impurity content. At 77°K, as‐sputtered films have three ESR centers, two HX centers, and an HY center. The HY center, a hole center, has g = 2.008–2.009. The HX center has two components, the HX_a center with axial symmetry and with ga_∥ = 2.022 and ga_⊥ = 2.037; the HX_b center with g_b = 1.984 which is split by hyperfine interaction with hydrogen. The hydrogen hyperfine interaction has axial symmetry, Ab_∥ = 30.2 G and Ab_⊥ = 63.6 G. Both the HX and HY centers show hyperfine splitting due to interaction with Si²⁹. Annealing of as‐sputtered films in hydrogen‐containing atmospheres at 350°C eliminates the HY center, leaving the HX center. Annealing in N₂ or O₂ at 550°C also eliminates the HY center; the resulting HX resonance is identical to that obtained after hydrogen anneal. The activation energy for the appearance of the HX center is 0.036 eV when samples are cooled to 77°K. From similarities in hyperfine interactions, activation energies, and g values, it is suggested that the HY center is the silicon analog of the Al center in SiO₂. It occurs in oxygen‐deficient SiO₂ and is due to removal of a nonbonding electron from an oxygen which bonds Si⁺³ to Si⁺⁴. The HY center is converted to the HX center by bonding with hydrogen which can be provided by H₂ from the annealing ambient or by the H atom in Si–OH incorporated in SiO₂ films.