Electronic Properties of a-SiOx Ny:H/SiN x Stacks for Surface Passivation of P-Type Crystalline Si Wafers

摘要

The surface passivation quality of plasma-enhanced chemical vapor-deposited silicon oxynitride/silicon nitride (a-SiOxNy:H/SiNx) stacks has been investigated for p-type float-zone crystalline silicon wafers. The effective lifetime τeff, density of fixed charge Qf, and density of interface defects Dit were measured as a function of the a-SiOxNy:H layer thickness both before and after firing at 800°C for 3 s. Photoluminescence imaging under applied bias has been used to characterize Qf and the surface recombination parameters S0n and S0p through fitting τeff versus voltage curves to an extended Shockley-Read-Hall (SRH) model. The results are in good agreement with values measured using capacitance-conductance-voltage measurements. Good surface passivation has been obtained with a peak effective lifetime of 2.41 ms. For both as-deposited and fired samples, Qf and Dit decrease with increasing a-SiOxNy:H layer thickness up to ~18 nm. The results indicate that the field-effect passivation is weakened as the a-SiOxNy:H thickness increases and that chemical passivation from a-SiOxNy:H/SiNx plays a prominent role. Increasing the a-SiOxNy:H/SiNx thickness to 50 nm produces similar results, indicating that an 18-nm interlayer is enough to obtain the desired passivation properties. Compared with as-deposited samples, fired samples exhibit lower Dit, indicating that the firing process enhances chemical passivation of the a-SiOxNy:H/SiNx stacks.