A modified inductively coupled plasma for high-speed, ultra-smooth reactive phase etching of silica glass

We report on the etching of borosilicate glass substrates in a conventional and modified inductively coupled plasma - reactive ion etch (ICP-RIE) tool. We present the etch rates and surface roughness of borosilicate glass in various fluorine based plasmas using C₄F₈, SF₆, Ar, NF₃, and H₂O gases. In the conventional ICP-RIE etching mode an etch rate of 0.55 μm/min at a rms surface roughness of 25 nm was obtained at C₄F₈, SF₆ flow rates of 5 sccm, O₂ flow rate of 50 sccm, 2000 W of ICP power, 475 W of substrate power. A maximum etch rate of 0.67μm/min was obtained at a high rms surface roughness of 450 nm by increasing flow rate of C₄F₈ to 50 sccm. Using the modified ICP-RIE system consisting of a gas diffuser ring clamped to the substrate holder, the physical component of the etching was considerably reduced and we have been able to achieve etch rates ~0.72 μm/min with surface smoothness of ~1 nm for borosilicate glass and fused silica respectively after 5 minutes etches.