Influence of hydrogen on the regeneration of boron-oxygen related defects in crystalline silicon

Abstract

When exposed to light, boron doped monocrystalline Czochralski grown silicon suffers from degradation of the minority carrier lifetime due to the formation of recombination active boron-oxygen related defects. The so called regeneration procedure is able to convert these recombination active defects into a new less recombination active state characterized by a higher minority charge carrier lifetime and stability under illumination. However, the exact working principle on microscopic scale is still unknown even though some influencing factors were identified. The role of hydrogen in the regeneration process is investigated in this work. We find that the characteristic regeneration time constant is subject to variation depending on the process parameters of a Plasma Enhanced Chemical Vapor Deposition a-SiNx:H deposition, namely the applied gas flows, as well as on the thermal history of the sample prior to applying the regeneration procedure. The positive effect of a short high temperature (800–900 °C) step leads to the idea that the presence of atomic hydrogen in the silicon bulk is crucial for the regeneration effect to occur. The different regeneration behavior of samples with variable thickness of a hydrogen diffusion barrier, namely an Al2O3 layer capped by SiNx:H, supports those results. Finally, the importance of hydrogen for regeneration is directly shown on samples having different hydrogen bulk concentrations due to direct hydrogenation in a Microwave Induced Remote Hydrogen Plasma reactor. A new model to explain the effect of the regeneration of boron-oxygen related defect centers based on the possible role of atomic hydrogen is presented.