Study of the plasma etching process for low-loss SiO2/Si optical waveguides

Deep etching of Ge-doped SiO2 using an epoxy based negative resist and a Chromium film as a mask in CHF3/O2 plasma has been investigated. Parameters varied in design that include radio-frequency (RF) power, gas ratio, work pressure and gas total flux, and the major etch responses including etch rate and selectivity are modeled. In the high etch rate and high selectivity reactive ion etching process, it was found that the bottom and sidewall surfaces were rough in the Cr mask etching because of physical sputtering of the Cr film by ion bombardment. In addition, a tapered facet on the etched sidewall of resist mask sample when the etching process goes on some extent that attributed to epoxy resist film degeneration induced by ion bombardment effects. A novel resist-on-Cr double-layer mask that can overcome the single-layer mask limitation is developed for enhancing the Ge-doped SiO2 etching result and improving the epoxy resist mask utilization. Based on studies, low-loss SiO2/Si channel waveguides with propagation loss of − 0.07 dB/cm are fabricated at last.