Abstract 13.56 MHz capacitance coupled Ar plasma irradiation at 50 W for 120 s caused serious damage at SiO2/Si interfaces for n-type 500-μm-thick silicon substrates. The 635-nm-light induced minority carrier effective lifetime (τeff) was decreased from 1.7 × 10−3 (initial) to 1.0 × 10−5 s by Ar plasma irradiation. Moreover, the capacitance response at 1 MHz alternative voltage as a function of the bias voltage (C–V) was changed to hysteresis characteristic associated with the density of charge injection type interface traps at the mid gap (Dit) at 9.1 × 1011 cm−2 eV−1. Subsequent 940-nm laser annealing at 3.7 × 104 W/cm2 for 4.0 × 10−3 s markedly increased τeff to 1.7 × 10−3 s and decreased Dit to 2.1 × 1010 cm−2 eV−1. The hysteresis phenomenon was reduced in C–V characteristics. Laser annealing effectively decreased the density of plasma induced carrier recombination and trap states. However, laser annealing with a high power intensity of 4.0 × 104 W/cm2 seriously caused a thermal damage associated with a low τeff and a high Dit with no hysteresis characteristic.