This study evaluates minority carrier lifetime in floating zone Si affected by advanced and conventional Si IGBT (insulated gate bipolar transistor) processes. Si gate oxidations reduce lifetime due to the formation of interface states between the Si and the oxide. As a result, cross-sectional photoluminescence imaging shows that the lifetime around a trench is lower than that in the bulk region. The high temperature thermal treatment for B-base/P-emitter layer activation after gate oxidation improved the interface, thus resulting in the recovery of the lifetime. TEM observations reveal that the (110) trench surface shows irregular contrast while the (100) surface shows relatively smooth contrast, which is consistent with the lifetime result of "trench side wall surface (100)" > "trench side wall surface (110)." Our study conclusively clarifies that lifetime is correlated with the SiO2 surface state. (C) 2019 The Japan Society of Applied Physics