Improvement of charge minority‐carrier lifetime in<i>p</i>(boron)‐type Czochralski silicon by rapid thermal annealing

Abstract

Abstract In p ‐type Czochralski‐grown (Cz) silicon a light‐induced degradation of the minority‐carrier lifetime is well known in the literature. Reducing the extent of this degradation would significantly improve the stable effective lifetime and thus the related performance of solar cells. In this work, the reduction of the density of the metastable defect underlying the degradation is performed by rapid thermal annealing (RTA). For a proper analysis it is extremely important to avoid contamination by the RTA furnace. Both, SiN x and SiO 2 were examined as a barrier layer. A 60 nm SiN x layer was proven to act as the most effective barrier layer, allowing maintenance of a very high lifetime of 700 μs on 1.25 Ω cm p ‐type FZ material. A design‐of‐experiments (DOE) study was used to analyze the effect of five process parameters on the stable effective lifetime. Especially, the plateau temperature shows a strong correlation with τ d , the stable effective lifetime after light‐induced degradation. The effect of plateau temperature on τ d of Cz‐ and FZ‐Si wafers is examined in the temperature range of 700–1050°C for plateau time 120 s. It was found that the stable effective lifetime of all RTA‐treated Cz‐wafers is increased compared with the initial stable effective lifetime before processing. The highest increase of stable effective lifetime (by a factor of around 2) is obtained at 900°C with a process time of 120 s. This increase in lifetime is reflected in a reduced concentration of the metastable defect. Copyright © 2001 John Wiley &amp; Sons, Ltd.