Analysis of the negative charges injected into a SiO2/SiNx stack using plasma charging technology for field‐effect passivation on a boron‐doped silicon surface

Abstract

AbstractWe investigated field‐effect passivation by injecting negative charges into SiO2/SiNx stack using a plasma charge injection technique. The Si/SiO2/SiNx samples exhibited a very high flat‐band shift with a high injected negative charge density (>3.0 × 1013 cm2) after plasma negative charge injection; this density was higher than that for the well‐known Al2O3 layer. Most injected negative charges were present within approximately 90 nm of the surface of the SiNx layer deposited by plasma‐enhanced chemical vapor deposition (PECVD) when comparing the capacitance–voltage analysis results obtained while etching the SiNx film considering four assumptions of the injected negative charge distribution. The saturation current density in a 90‐ohm/sq boron emitter decreased from ~90 to 50 fA/cm2 after negative charge injection, which is equivalent to the J0e of the structure passivated with an Al2O3/SiNx stack. Six‐inch n‐type bifacial cells with an approximately 100‐ohm/sq boron emitter passivated with SiO2/SiNx displayed an approximately 0.2% increase in absolute cell efficiency after negative charge injection. In addition, n‐PERT bifacial cells with a high boron sheet resistance of ~150 ohm/sq exhibited a 1.0% or higher absolute efficiency enhancement from a relatively low precharging efficiency of approximately 19.0%. We also demonstrated that the final efficiency after charging was comparable with n‐PERT bifacial cells with Al2O3 passivation, suggesting that the proposed process is a potential low‐cost alternative method that could replace expensive Al2O3 processes.