Inductively coupled plasma etching for arrayed waveguide gratings fabrication in silica on silicon technology

Abstract

Arrayed waveguide gratings (AWGs) in silica on silicon technology were fabricated and tested in our laboratory. The silica optical layers were all deposited in low-pressure chemical vapor deposition furnaces, and waveguide core was etched using a photoresist mask in an inductively coupled plasma source with C4F8/O2/He gas mixture. This article reports the dependence of important process parameters, including aspect ratio dependent etch rate (ARDE) effect, selectivity, and waveguide sidewall angle, on rf power, chamber pressure, and gas flow rates. In particular, the effects of He and O2 addition on ARDE effect and waveguide sidewall angle were investigated. Based on these results, a reliable and high throughput process was set up to etch silica waveguides suitable for AWG fabrication, with etch rate higher than 300 nm/min, selectivity on photoresist higher than 5:1, and waveguide sidewall angle higher than 88.5°. Measurements of the first 16 channel 200 GHz AWGs fabricated with this process are presented and discussed. To conclude, preliminary results are reported about etching of high aspect ratio (>3:1) trenches with depths greater than 15 μm, to be used for stress releasing grooves in AWGs.