Ultrathin silicon oxide prepared by in-line plasma-assisted N2O oxidation (PANO) and the application for n-type polysilicon passivated contact

Abstract

We develop a plasma-assisted nitrous-oxide (N2O) gas oxidation (PANO) method to prepare the ultrathin silicon oxide (SiOx) for polysilicon (poly-Si) passivated contact. The effects of preparation conditions, including the substrate temperature, processing time, and plasma power, are studied. Afterwards, we integrate the PANO SiOx into the polysilicon passivated contact and optimize the passivation and contact performances. Excellent surface passivation with the n-type poly-Si and PANO SiOx on the n-type c-Si wafer is achieved by 880 °C annealing, which shows competitive passivation quality to the one with NASO SiOx. Champion implied open-circuit voltage (iVoc) and single-sided recombination saturated current (J0) reach 730 mV and 4.3 fA/cm2 after crystallization; and they are further improved to 747 mV and 2.0 fA/cm2 (3 × 1015cm−3) after subsequent AlOx/SiNx hydrogenation. Using transmission electron microscopy (TEM), we find that the thickness of PANO SiOx ranges 1.1–2.4 nm and the controlled nitric acid oxidized SiOx (NAOS) ranges 1.3–1.8 nm. The contact resistivity (ρc) is typically <10 mΩ cm2 with the annealing temperature of >820 °C. Also, the crystallinity, phosphorous in-diffusion profile, and current-leaking density of the passivated contacts are investigated. In general, the PANO SiOx and in-situ doping amorphous silicon precursor can be fabricated in one PECVD system without additional equipment or transfer procedures, which is favorable for the high-efficiency, low-cost industrial manufacture.