Etching studies of silica glasses in SF6/Ar inductively coupled plasmas: Implications for microfluidic devices fabrication

To fabricate microlaboratories, commercially available silica glasses represent a good alternative to the expensive quartz or fused silica substrates. Therefore, the authors have here investigated the behavior of four of them-Vycor, Pyrex, D263, and AF45-in SF6 and SF6/Ar inductively coupled plasmas. Using Vycor, a material close to pure SiO2, as a reference, they demonstrated that the etch rate negatively correlates with the global content in metallic oxides. However, no such clear trend was found for the surface roughness and they hypothesize that the large asperities (>500 nm) sometimes observed might be due to local variation in the glass surface composition. Furthermore, investigations on the influence of the plasma conditions (i.e.,source power, dc self-bias, gas mixture, and pressure) on the etch rate, surface chemistry, and surface morphology, as well as positive ion current and fluorine concentration measurements, enable them to unravel an ion enhanced chemical etching mechanism, where stronger ion assistance is needed when more metallic oxides are present. By increasing the ion to neutral flux ratio, they consequently could, for all the materials, reduce the surface roughness to less than 5 nm while maintaining etch rates around 150 nm/min. These conditions have further been used to optimize pattern transfer experiments. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3298875]