Effective antireflection and surface passivation of silicon using a SiO2/a-TiOx film stack

This article reports an effective and industrially relevant passivation and anti-reflection film stack featuring a 10 nm silicon dioxide (SiO2) film followed by a »65 nm amorphous titanium oxide (a-TiOx) film. This film stack has equivalent optical performance to a single-layer silicon nitride (SiNx) antireflection coating (ARC) for unencapsulated cells, and slightly better performance for encapsulated cells (»0.2 mA×cm-2 increase). The field effect passivation properties of the SiO2/aTiOx film stack have been modified extrinsically after the film deposition to demonstrate surface recombination velocities below 1.2 cm/s in a 1 Ω·cm n-type silicon wafer. Finally, the TiOx films have been deposited using an in-line atmospheric pressure chemical vapor deposition (APCVD) system at temperatures below 350o C, thus demonstrating this film stack offers both better passivation and optical performance, as well as a potentially lower manufacturing cost compared to SiNx, due to the use of APCVD rather than plasma-enhanced chemical vapor deposition. Simulations indicate further gains in terms of optical performance (»0.3 mA×cm-2 increase compared to SiNx – encapsulated case) may be possible using a double-layer ARC featuring a polycrystalline TiOx (pc-TiOx) film followed by an aluminum oxide (AlOx). However, potential contamination from the APCVD may pose a risk to maintaining high bulk carrier lifetimes.