Influence of firing temperature on APCVD poly-Si properties for fired passivating contacts

Abstract

We demonstrate the usage of boron-doped polycrystalline-silicon (poly-Si) fabricated by atmospheric pressure chemical vapor deposition for the formation of fired passivating contacts. Layers of different thicknesses are studied regarding their crystallite size, resistivity, and passivation properties for different fast firing temperatures. From X-ray diffraction measurements, it is concluded quantitatively that a higher firing peak temperature increases the crystallite size of the poly-Si to values up to 10 nm. This change in crystallite size varies inversely proportional with the resistivity, which is drastically decreased for higher firing temperatures. Higher implied open circuit voltages (iVOC) and lower saturation current densities (J0) are found for thinner poly-Si layers and at higher firing temperatures, most probably due to a difference in hydrogen diffusion time from the SiNX:H layer to the interface oxide. Although no blisters of the (p) poly-Si are observed, blistering of the SiNX:H layer at high firing temperatures >900°C impairs the passivation for thin layers. A maximum iVOC of 708 mV and minimum J0 of ∼12 fA/cm2 are achieved.