Dry etching of polydimethylsiloxane using microwave plasma

This paper presents a new polydimethylsiloxane (PDMS) dry-etching method that uses microwave plasma. The applicability of the method for fabricating microstructures and removing residual PDMS is also verified. The etch rate of PDMS was dominantly influenced by the gas flux ratio of CF4/O-2 and the microwave power. While the PDMS etch rate increased as the flux ratio of CF4 was increased, the etch rate decreased as the flux ratio of O-2 was increased. The maximum etch rate of 4.31 mu m min(-1) was achieved when mixing oxygen (O-2) and tetrafluoromethane (CF4) at a 1: 2 ratio at 800 W power. The PDMS etch rate almost linearly increased with the microwave power. The ratio of the vertical etch rate to the lateral etch rate was in a range of 1.14-1.64 and varied with the gas fluxes. In consideration of potential applications of the proposed PDMS etching method, array-type PDMS microwells and network-type microprotrusion structures were fabricated. The contact angle was dramatically increased from 104 degrees (non-etched PDMS surface) to 148 degrees (etched PDMS surface) and the surface was thereby modified to be superhydrophobic. In addition, a thin PDMS skin that blocked holes and PDMS residues affixed in nickel microstructures was successively removed.