Selective etching of PDMS: Etching technique for application as a positive tone resist

Abstract

Although, poly(dimethylsiloxane) (PDMS) is a widely used material in numerous applications, such as micro- or nanofabrication, the method of its selective etching has not been known up to now. In this work authors present two methods of etching the pure, additive-free and cured PDMS as a positive resist material.To achieve the chemical modification of the polymer necessary for selective etching, energetic ions were used. We created 7 μm and 45 μm thick PDMS layers and patterned them by a focused proton microbeam with various, relatively large fluences. In this paper authors demonstrate that 30 wt% Potassium Hydroxide (KOH) or 30 wt% sodium hydroxide (NaOH) at 70 °C temperature etch proton irradiated PDMS selectively, and remove the chemically sufficiently modified areas. In case of KOH development, the maximum etching rate was approximately 3.5 μm/min and it occurs at about 7.5 × 1015 ion × cm−2. In case of NaOH etching the maximum etching rate is slightly lower, 1.75 μm/min and can be found at the slightly higher fluence of 8.75 × 1015 ion × cm−2.These results are of high importance since up to this time it has not been known how to develop the additive-free, cross-linked poly(dimethylsiloxane) in lithography as a positive tone resist material.