Limiting Factors of Backside External Gettering by Nanocavities and Aluminum-Silicon Alloying in Silicon Wafers

Abstract

Float zone silicon single crystalline wafers are submitted to He ion implantations at various energy levels and fluences in the ranges 40 to 120 keV and 1016 to 1017 cm−2, respectively. Cavities are formed after annealing at 900°C for 1 h in argon. Al-Si gettering results from the deposition of a backside 1 µm thick Al wafer and annealing at 900'C for 4 h in argon. The wafers are voluntarily contaminated by 1014 to 1017 cm−3nickel atoms and diffusion length of minority carriers is determined by SPV technique and measured before and after gettering.It is found that gettering by cavities works fairly well provided the fluence is 1017 cm−2. The gettering efficiency decreases in heavily contaminated samples suggesting that the capture of impurities by the cavities is limited by the saturation of their internal surface. Al-Si alloying appears more efficient at higher contamination levels. This is most likely due to the high solubility of metal atoms in the liquid Al-Si alloy formed during the annealing.