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

We 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 x 10(13)cm(2)) 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 similar to 90 to 50 fA/cm(2) after negative charge injection, which is equivalent to theJ(0e)of the structure passivated with an Al2O3/SiNx stack. Six-inchn-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 similar to 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 withn-PERT bifacial cells with Al2O3 passivation, suggesting that the proposed process is a potential low-cost alternative method that could replace expensive Al2O3 processes.