Hydrogen in stacked dielectric layers

Abstract

Hydrogen plays a major role for passivation of silicon surfaces. The hydrogen needed for passivation is usually delivered by hydrogenated dielectric layers which are deposited on the silicon surface. The absolute concentration of hydrogen within the layers as well as the change in concentration and hydrogen bond structure due to firing or annealing steps are important factors for surface and volume passivation quality. Our recent work demonstrates major gains in passivation quality of stacked dielectric layers using a silicon oxide (SiO2) capping layer compared to single layer systems [1,2]. As these stacked systems can be used as double layer anti-reflection coatings they are interesting for solar cell production. This study focuses on passivation layer stacks consisting of plasmaenhanced chemical vapour deposition (PECVD) hydrogenated silicon nitride (SiNx) capped with PECVD SiO2. Improved performance on stacked layer lifetime samples and solar cells on minority carrier lifetime level and Voc compared to samples with single SiNx layers, require a deeper look into the hydrogen kinetics and bonding structure. Fourier transform infrared spectroscopy (FTIR) and nuclear resonance reaction analysis (NRRA) reveal considerable differences in the bond density change due to firing and higher hydrogen concentrations at the silicon/dielectric interface of stacked systems compared to single layer anti-reflection coatings.