Nanoindentation and Stability Response of Sub-100 nm PECVD-Grown Silicon Nitride Single- and Double-Layer Antireflection Coatings

This study presents a comprehensive mechanical and environmental stability assessment of sub-100 nm PECVD-grown silicon nitride (SiNx) antireflection coatings in single-layer (SLAR) and double-layer (DLAR) configurations for photovoltaic applications. Nanoindentation was performed on SiNx SLAR 75 nm with refractive index as 2.05 and SiNx DLAR as 55 nm/30 nm, R.I = 1.90/2.10 for top and bottom layer films following deposition temperature ranging from 300 to 400 °C. SiNx SLAR thin film exhibited excellent thermal resilience with hardness decreasing only slightly (15.845–15.666 GPa) and reduced modulus remaining stable (∼165 GPa), while SiNx DLAR coatings showed softening with an ∼2.3 GPa drop in hardness and ∼10 GPa in modulus, attributed to hydrogen effusion and matrix relaxation. Mean contact depths remained within 30% of the film thickness, validating the Oliver–Pharr modeling. AFM scans confirmed dense, defect-free surfaces with Rq 0.704 nm for SiNx SLAR and 0.355 nm for DLAR, establishing a high-quality baseline for durability tests. Under damp heat aging (85 °C/85% RH), minority carrier lifetime declined by 4.41% in SiNx SLAR and 2.65% DLAR, with subsequent H2-forming gas annealing enabling a partial recovery of 4.13% for SLAR and 2.59% for DLAR. These findings highlight the need to balance mechanical durability and thermal stability in designing reliable antireflection coatings for high-efficiency silicon solar cells.