Rapid thermal annealing of spin-coated phosphoric acid films for shallow junction formation

Rapid thermal annealing (RTA) of spin-coated phosphoric acid (H3PO4) films on silicon substrates has been studied for the formation of shallow junctions. The junctions are characterized by spreading resistance profiling. Device quality, shallow (<0.2 μm), n+p junctions are formed by the resulting phosphorous diffusion with the junction depth and surface concentration depending on the RTA conditions. The films have been studied by Fourier transform infrared spectroscopy after various RTA treatments. The presence of P=O bonds in the films becomes evident after the RTA treatment at elevated temperatures (>750 °C), below which absorption bands originating from water species are noted. More than 15% efficient, shallow emitter, large-area (10 cm×10 cm) n+pp+ silicon solar cells are fabricated with a short-time processing using this rapid thermal processing technique.