Surface improvement investigation of sol-gel SiO₂ cladding for waveguide device passivation

The sol-gel method is a well-known process for SiO₂ formation on top of a semiconductor-based waveguide. This method does not require expensive equipment or SiH₄ gas. However, it may result in difficulty with wet-etching, which prevents proper current injection into the semiconductor layer. We have investigated the surface condition of sol-gel SiO₂ on top of Si, and have confirmed that the main causes of the anti-etching property might be due to the formation of a polymer layer after the curing process. To improve the surface condition, plasma ashing, in addition to 700 °C curing, is proposed. Regular wet etching of SiO₂ layer on Si with a ratio of 1800 nm min^-1 has been successfully confirmed.