Effect of Deep-Level Defects on Surface Recombination Velocity at the Interface Between Silicon and Dielectric Films

The surface recombination velocity (SRV) characteristic of deep-level defects at Si interfaces with dielectric thin films was obtained from conductance measurements on metal-insulator-semiconductor capacitor (MISCAP) devices. The dielectrics in contact with Si were thermal SiO₂ (Tox), chemical SiO₂, and atomic layer deposition (ALD) Al₂O₃, which were annealed and exposed to a low flux of X-rays. A modified conductance technique was developed in which a large ac signal was superimposed on a dc bias and the surface potential was swept across the band gap of a MISCAP from near accumulation to deep depletion. The frequency-dependent energy loss due to all defects across the band gap and their correlations were measured using the effective equivalent conductance. A model containing one resistor and one capacitor was sufficient to describe the frequency-dependent energy losses due to defects with similar activities. The total SRV was 112 ± 19 cm/s for Si/Tox, 1045 ± 150 cm/s for Si/chemical SiO₂/Al₂O₃, and 578 ± 96 cm/s for Si/Al₂O₃ interfaces. After forming gas annealing at 400°C, the SRV decreased to ~ 1 cm/s for both Si/Tox and Si/chemical SiO₂/Al₂O₃ and 47 ± 6 cm/s for Si/Al₂O₃. Vacuum annealing improved the Si/chemical SiO₂/Al₂O₃ interface but had an adverse effect on Si/Al₂O₃. Soft X-ray exposure increased the SRV of both Si/chemical SiO₂/Al₂ O₃ and Si/Al₂O₃.