Investigating Wafer Quality in Industrial Czochralski-Grown Gallium-Doped p-Type Silicon Ingots with Melt Recharging

Abstract

Herein, a systematic study of the electronic quality of gallium-doped p-type silicon wafers from Czochralski-grown ingots with melt recharging is presented. It is found that in the as-grown state, the ingots contain interstitial iron concentrations in the range of 3 × 109–2 × 1010 cm−3, with a trend of slightly higher concentrations toward the tail end of each ingot, and in subsequently grown ingots. However, analysis of the effective lifetimes indicates that iron–gallium pairs are not the dominant recombination centers in the as-grown state. Moreover, when these wafers are subjected to a tabula rasa step, an increase in the iron concentration is observed in the range of 1 × 1010–6 × 1010 cm−3, with iron–gallium pairs becoming the dominant recombination centers. This is possibly caused by the dissolution of pre-existing precipitated iron in the wafers. Nevertheless, the negative impact of iron contamination can be dramatically reduced by subjecting the wafers to a phosphorus diffusion gettering step, as is commonly incorporated in the fabrication of p-type passivated emitter and rear cells. Therefore, it is concluded that the quality of the ingots is not limited by iron contamination, even after multiple ingots are pulled from the recharged melt.