Iron precipitation in float zone grown silicon

Abstract

Temperature dependent iron precipitation in float zone grown silicon wafers has been experimentally investigated. Results of iron precipitation experiments over a wide thermal process temperature range and time are presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photovoltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 10 11 -10 13 atoms/cm 3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500-600°C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 min.

Surface photovoltage phenomena: theory, experiment, and applications

“…In addition, surface contamination of Fe has been investigated using SPV (albeit in a destructive manner) by performing a rapid thermal annealing Fe drive-in step prior to SPV measurements [12,428,488,498± 500]. Fe and Fe-silicide precipitation in Si wafers has also been examined recently [501,502].…”

Improvement of multicrystalline silicon solar cells by a low temperature anneal after emitter diffusion

“…Photoluminescence images revealed an improvement of the minority carrier lifetime in regions without grain boundaries or dislocation clusters. The effect was attributed to a reprecipitation of impurities 3. In precipitated form, one expects a smaller negative impact of a given amount of metals compared to the dissolved state, because only the precipitate surfaces act as recombination sites.…”

Precipitation of Interstitial Iron in Multicrystalline Silicon

“…Internal gettering of iron, by a low temperature annealing process, has been shown to be effective in reducing the interstitial iron concentrations and thus improve the minority carrier lifetimes in both mono-and multi-crystalline silicon materials [1][2][3][4]. These studies [1][2][3][4] have found that the optimal annealing temperature lies in the range of 500 o C-600 o C, where the Fe point defects have sufficiently high diffusivity to move to the precipitation sites and the Fe solubility is low enough to cause precipitation to occur. In multicrystalline silicon (mc-Si), the precipitation sites are mainly the structural defects within the material.…”