Coulombic and neutral electron trapping centers in SiO₂

Metal-oxide-semiconductor (MOS) structures incorporating thermally grown silicon dioxide (SiO2) films were implanted with arsenic ions (As+) and then annealed at high temperatures. Coulombic-attractive traps (for electrons) were produced with the avalanche injection of holes from the silicon substrate and their subsequent capture on some of these arsenic-related sites. During internal photo-emission of electrons from a thin aluminum gate, the voltage shifts due to hole annihilation by electrons were recorded and the macroscopic capture cross-section, σ, was determined. We found that σ varies from ∼10-12 to 3 × 10-15 cm2 for average electric fields ranging from 2 × 105 to 3 × 106 V/cm. Below an average field threshold of Fth ≈ 1.2 × 106 V/cm, the capture cross-section versus average field (σ versus Fave) dependence follows a power law with the exponent n ≈ -1.5. Above the average field threshold, the power law exponent was found to be n ≈ -3.0. Also when the amphoteric arsenic-related sites are empty, they form neutral trapping sites for electrons. For average fields ranging from 5 × 105 to 6 × 106 V/cm, the neutral cross-section is found to be approximately constant at σ ≈ (1-2) × 10-15 cm2. © 1989.