Investigation of Silicon Surface Passivation by Microwave Annealing Using Multiple-Wavelength Light-Induced Carrier Lifetime Measurement

Abstract

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.

Heat treatment in 110 °C liquid water used for passivating silicon surfaces

“…2 [35][36][37]. The system had waveguide tubes, which had a narrow gap for placing a sample for s eff measurement.…”

“…Microwave transmission in a dark field, T d and under LD light illumination, T p were detected and analyzed to obtain s eff . We constructed a finite element numerical calculation program including theories of carrier generation associated with optical absorption coefficients, carrier diffusion, and annihilation to estimate the surface recombination velocity S at the top and rear surfaces [35][36][37][38][39]. The most probable S was determined by the best coincidence between the experimental and calculated s eff values.…”

Heat treatment in 110°C liquid water used for passivating silicon surfaces

“…In order to measure τ eff precisely, we used a 9.35 GHz microwave transmittance measurement system [16][17][18]. The system had waveguide tubes, which had a narrow gap for placing a sample to measure τ eff .…”

Passivation of silicon surfaces by heat treatment in boiled water and its application of solar cells

“…In order to measure τ eff precisely, we used a 9.35-GHz microwave transmittance measurement system [14][15][16]. The system had waveguide tubes, which had a narrow gap for placing a sample to measure τ eff .…”

“…The penetration depth at 635 nm was about 3 μm, while it is very deep of 125 μm for 980 nm light [17]. We constructed a finite-element numerical calculation program including theories of carrier generation associated with optical absorption coefficients, carrier diffusion, and annihilation for estimating the surface recombination velocity at the top surface S top and the rear surface S rear [16]. Optical reflectivity spectra were measured between 250 and 1000 nm using a conventional spectrometer to estimate the oxide thickness formed by heat treatment in boiled water.…”