Influence of hydrogenated passivation layers on the regeneration of boron-oxygen related defects

When exposed to light, boron-doped monocrystalline Czochralski grown silicon suffers from degradation of the minority carrier lifetime due to formation of recombination active boron-oxygen related defects. The so called regeneration procedure is often able to convert these recombination active defects into a new less recombination active state characterized by the higher original minority carrier lifetime and being stable under illumination. The regeneration behavior of silicon wafers passivated with different dielectric layers is investigated in this work. We found that the characteristic regeneration time constant is subject to variation depending on the surface passivation layers used and the temperature steps applied prior to the regeneration procedure. Namely, a positive effect of a short high temperature (800-900 degrees C) firing step is shown as well as the influence of SiNx:H layer density. In addition to that, results are presented that suggest a negative effect of Al2O3/SiNx:H stacks depending on the thickness of the Al2O3 interlayer. All three effects are attributed to the influence of the respective processes on the hydrogen content in the silicon bulk. A hypothesis to explain the effect of the regeneration of boron-oxygen related defect centers including a possible role of hydrogen is presented. This includes the assumption of regeneration actually being hydrogen passivation of boron-oxygen related defects, triggered by carrier injection in combination with slightly elevated temperatures. (C) 2013 The Authors. Published by Elsevier Ltd.