Fabrication and performance of p+ layer by SiO2 nanospheres assisted liquid boron diffusion

Boric acid mixed with SiO₂ nanospheres was used as a boron source in the spin-on method to improve p⁺ layer doping quality in the surface of p-type single crystal silicon (c-Si) wafers with pyramid structure texture. The effects of boric acid concentration, diffusion temperature and diffusion time on diffusion uniformity, surface hole concentration, junction depth and minority carrier lifetime were investigated. It was found that the addition of SiO₂ nanospheres in boric acid could result in a high degree of diffusion uniformity more than 96%. When the boric acid concentration was 5 g/100 mL and diffusion was at 940 °C for 40 min, the obtained p⁺ layer in silicon wafer showed a best overall performance with a surface hole concentration of 8 × 10¹⁸ cm⁻³, a sheet resistance (R_S) of 70.2 Ω/□, a junction depth of 0.28 μm and minority carrier lifetime of 3.39 μs.