Photoresist etching with dielectric barrier discharges in oxygen

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Abstract
This article presents results on the surfaceetching of a Novolak-type polymer (Shipley, SPR2) on Si wafers using dielectric barrier discharges in oxygen at high pressures and room temperature. The etching depth is measured by mechanical profilometry as a function of gap spacing and gas pressure. Figures of merit are generated allowing comparison with conventional plasmasurface treatment, as etch rate per power density coupled onto the sample surface ( nm J −1 cm 2 ), or coupled into the gas volume ( nm J −1 cm 3 ). Energy-density specific etch rates were measured as a function of the gap spacing (d) and the total oxygen gas pressure (p), as well as a function of the product of pd in the gas pressure range of 50–1500 mbar and of the gap spacing range of 1–20 mm. At a constant gap spacing and pressure, the removal rate is a linear function of the applied power density. The highest achieved etching rate per surface energy density is 2.2 nm J −1 cm 2 at 730 mbar and 1 mm (0.2 nm J −1 cm 3 ) and the highest etching rate per volumetric energy density is 0.85 nm J −1 cm 3 at 290 mbar and 7 mm (0.87 nm J −1 cm 2 ). The surface of the etchedphotoresist is characterized using mechanical profilometry and scanning electron microscopy. The results obtained in this work suggest that dielectric barrier discharges can be an efficient, alternative plasma source for general surface processing, because they can provide nonthermal discharges also near atmospheric pressures and thereby eliminate the need of costly vacuum systems.

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