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

Abstract

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 C ₄ F ₈ , SF ₆ , Ar, NF ₃ , and H ₂ O 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 C ₄ F ₈ , SF ₆ flow rates of 5 sccm, O ₂ 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 C ₄ F ₈ 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.