Hydrogenation of Si/SiO 2 interface using HF-etched wafer as a source of hydrogen

Abstract Surface passivation plays an important role in solar cell efficiency, and a well-established surface passivation technique is using the silicon oxide layer. The ultrathin layer of so-called tunnel oxide is a core of very promising TOPCon technology. As a part of the technology, is a post-hydrogenation process that has been extensively developed and is utilized to mitigate the dangling bonds and other surface impurities mainly at the interface between silicon and oxide layer. Even though these commercial processes are very effective in terms of enhancing the silicon solar cell performance, they require extra layer deposition, firing step followed by layer removal. This work introduces the sandwiching process, a tunnel oxide hydrogenation approach in which a Si wafer bearing a chemical tunnel oxide is positioned between HF-etched wafers serving as hydrogen sources and subjected to a 650 °C anneal for 15 min. This process leads to achieving the effective carrier lifetimes of 0.1 ms. We have varied temperature conditions from 450 °C–850 °C to investigate the trade-off between the hydrogenation process and thermal oxidation that is a competing process. At 650 °C, we successfully maintained the desired oxide thickness between 1 nm and 2 nm along with a reliable carrier lifetime(∼100 μs), exhibiting an error variation of ±5%. Although the measured carrier lifetime decreases by nearly 50% from its initial value i.e. ∼100 μs, it exhibits relative temporal stability over a duration of up to 250 min. FTIR surface analysis of the sandwiched wafer confirms that the sandwiching process introduces additional hydrogen into the SiO 2 layer at the Si/SiO 2 interface.