Effects of low temperature anneal on the interface properties of thermal silicon oxide for silicon surface passivation

High quality surface passivation has gained a significant importance in photovoltaic industry for reducing the surface recombination and hence fabricating low cost and high efficiency solar cells using thinner wafers. The formation of good-quality SiO₂ films and SiO₂/Si interfaces at low processing temperatures is a prerequisite for improving the conversion efficiency of industrial solar cells with better passivation. High-temperature annealing in inert ambient is promising to improve the SiO₂/Si interface. However, annealing treatments could cause negative effects on SiO₂/Si interfaces due to its chemical at high temperatures. Low temperature post oxidation annealing has been carried out to investigate the structural and interface properties of Si-SiO₂ system. Quasi Steady State Photo Conductance measurements shows a promising effective carrier lifetime of 420 μs, surface recombination velocity of 22 cm/s and a low interface trap density (D_it) of 4×10¹¹ states/cm²/eV after annealing. The fixed oxide charge density was reduced to 1×10¹¹/cm² due to the annealing at 500 °C. The FWHM and the Si-O peak wavenumber corresponding to the samples annealed at 500°C reveals that the Si dangling bonds in the SiO₂ films due to the oxygen defects was reduced by the low temperature post oxidation annealing.