Dry etching of polydimethylsiloxane using microwave plasma

Abstract

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 CF 4 /O 2 and the microwave power. While the PDMS etch rate increased as the flux ratio of CF 4 was increased, the etch rate decreased as the flux ratio of O 2 was increased. The maximum etch rate of 4.31 μm min −1 was achieved when mixing oxygen (O 2 ) and tetrafluoromethane (CF 4 ) 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 • (non-etched PDMS surface) to 148 • (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.

Implementation of PDMS-based Slanted Edge-type Microelectrode Array for Neural Stimulation

“…This phenomenon can lead to irreversible cell damage during neural stimulation and electrode damage in certain areas of the electrode. Therefore, an electrode structure with more uniform current density distribution is required, which can be achieved by slanted-edge electrodes [12].…”

“…Then, the surface of the PDMS is etched by about 1 μm using a tetrabutylammonium fluoride (TBAF) solution and the sacrificial post is removed. Finally, the outline of the electrode is cut using a ND:YVO4 laser [12]. The detailed process sequence is shown in Figure 1.…”

“…To adjust the mask distance, a 160-μm-thick PET film was used between the mask and photoresist layer. By adjusting the exposure time and the exposure distance, it is possible to manufacture sacrificial posts having various inclination angles [12]. Figure 4 shows the fabricated sacrificial posts.…”

“…Polymer-based electrodes have been recently studied for these reasons [8][9][10][11][12]. These electrodes are commonly fabricated with an insulator-conductor-insulator sandwich-like structure.…”

“…Polyimide and parylene polymers are widely used as the insulators owing to their high biocompatibility and easy fabrication process. However, PDMS has attracted much attention as the base material for inserted electrodes because it has excellent biocompatibility and its Young's modulus is very similar to that of nerve tissue [10,12]. It is used for medical applications and food additives, and is certified by the FDA.…”