Minority-carrier lifetime optimization in silicon MOS devices by intrinsic gettering

Abstract

The effect of intrinsic gettering on the minority-carrier generation lifetime ( τ g) of Si MOS devices fabricated on CZ and HMCZ Si substrates of varying interstitial oxygen concentration was investigated. Wafers cut from 57 mm diameter Si ingots grown under a horizontal magnetic field of B=0 to B=5.4 kG were divided into three groups according to the initial interstitial oxygen concentration: low oxygen (8–12 ppma (New ASTM)), medium oxygen (13–17 ppma), and high oxygen (18–20 ppma). When subjected to an intrinsic gettering method consisting of 1150°C/1 h denudation and 650°C/1 h nucleation preanneal followed by 1000°C/11 h process simulation anneal, the medium-oxygen CZ Si specimens by far showed the best intrinsic gettering effect, yielding a generation lifetime ( τ g) of 26.7 μs as compared to those of 5 μs or less observed in other specimens. Apparently, the low-oxygen CZ Si specimens lacked sufficient SiO x nuclei to cause oxygen precipitation required for intrinsic gettering, while the high-oxygen CZ Si specimens had too many SiO x nuclei to cause the oxygen precipitation terminate prematurely during the 1000°C/11 h process simulation step. As for the HMCZ Si specimens, on the other hand, the lack of grown-in defects, which may work well for nongettering processes, is believed to have muted the effect of the intrinsic gettering heat treatment.