A simple annealing method using a commercial 2.45 GHz microwave oven is reported to increase the minority carrier lifetime eff for 4-in.-size 500m-thick 20 cm n-type silicon substrates coated with 100-nm-thermally grown SiO 2 layers. The microwave annealing was conducted with 2-mmthick glass substrates, which sandwiched a silicon sample to maintain the thermal energy in silicon and realize gradual cooling. A 9.35 GHz microwave transmittance measurement system was used to measure eff in the cases of continuous-wave 635 and 980 nm laser diode (LD) light illuminations. Radio-frequency Ar plasma irradiation at 50 W for 60 s to the top surface of a silicon sample markedly decreased eff in the range from 6:0 Â 10 À6 to 2:4 Â 10 À5 s and from 4:2 Â 10 À5 to 6:4 Â 10 À5 s in the cases of 635 and 980 nm light illuminations, respectively, while eff had the same distribution from 1:6 Â 10 À3 to 3:1 Â 10 À3 s for the initial samples. The finite element numerical analysis revealed that Ar plasma irradiation caused high densities of recombination defect states at the silicon top surface in the range from 1:3 Â 10 13 to 5:0 Â 10 13 cm À2. Microwave annealing at 700 W for 120 s markedly increased eff in the range from 8:0 Â 10 À4 to 2:5 Â 10 À3 s, which were close to those of the initial samples. The density of recombination defect states was well decreased by microwave annealing to low values in the range from 7:0 Â 10 10 to 3:4 Â 10 11 cm À2. The high eff achieved by microwave annealing was maintained for a long time above 5000 h.
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