Effective Antireflection and Surface Passivation of Silicon Using a SiO2/a-T iOx Film Stack

This paper reports an effective and industrially relevant passivation and antireflection film stack featuring a 10 nm silicon dioxide (SiO
₂
) film followed by a ≈65 nm amorphous titanium oxide (a-TiO
_x
) film. This film stack has equivalent optical performance to a single-layer silicon nitride (SiN
_x
) 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 SiO
₂
/a-TiO
_x
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 TiO
_x
films have been deposited using an inline atmospheric pressure chemical vapor deposition (APCVD) system at temperatures below 350 °C, thus demonstrating this film stack offers both better passivation and optical performance, as well as a potentially lower manufacturing cost compared to SiN
_x
, 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 SiN
_x
-encapsulated case) may be possible using a double-layer ARC featuring a polycrystalline TiO
_x
film followed by an aluminum oxide (AlO
_x
). However, potential contamination from the APCVD may pose a risk to maintaining high bulk carrier lifetimes.