Effects of minute impurities (H, OH, F) on SiO2/Si interface as investigated by nuclear resonant reaction and electron spin resonance

The effects of minute amounts of impurities (H, OH, and F) in SiO ₂ are investigated to obtain a guideline for improving the reliability of MOS devices. To examine the behavior of hydrogen, deuterium (D) is adopted as a tracer. The quantity of deuterium dissolved in SiO₂ is measured by the D(³He,p)⁴He nuclear resonant reaction (NRR) technique. The Influence of the impurities on the SiO₂-Si interface structure is studied by electron spin resonance (ESR) measurement. Hot-carrier injection with MOS capacitors and transistors are examined to determine the effects of minute impurities on the electrical characteristics of gate SiO₂ and the correlation of this effect with the NRR and ESR experimental results. It was found that significant amounts of D₂O are diffused into SiO₂ , even at 200°C, and these dissolved D₂O molecules are eliminated at temperatures above 700°C. The number of unpaired bonds at the interface increases with decrease of dissolved water in SiO ₂. The disappearance of the interface traps after high-temperature annealing above 800°C is thought to be due to the viscous flow of SiO₂ and to the interface reoxidation. Reducing the hydrogen and relaxing the interface strain are essential for improving the MOS device endurance against hot carriers