Deep reactive ion etching of commercial PMMA in O2/CHF3, and O2/Ar-based discharges

The reactive ion etching of PMMA in O2, O2/CHF3 and O2/Ar discharges has been examined as a function of bias voltage, flow rate and composition of the gas mixtures. Etching in O2, O2/CHF3 and O2/Ar plasmas (with a flow ratio of Ar/O2 ≤ 50%) shows higher ion-enhanced chemical etching dependence than in O2/Ar (with a flow ratio of Ar/O2 ≥ 50%). In Ar/O2 plasmas, with an increasing proportion of Ar, the dominant process changed from an ion-enhanced chemical process with high values of etch rate to a physical sputtering etch process. PMMA etched in O2 (10 sccm)/Ar (40 sccm) produced a smooth and vertical sidewall. With an increasing amount of CHF3, the etch rates of PMMA show a larger dependence on physical sputtering and a gradual decrease. When the depth of PMMA etched in O2 (25 sccm)/CHF3 (25 sccm) is about 100 µm the profile is vertical, but the sidewall surface is rough.