Removal of SU-8 by two types of hot-wire atomic hydrogen sources - Dissection of contributions by atomic hydrogen and substrate heating

The removal of the permanent photoresist SU-8 by atomic hydrogen was studied using hot-wire reactors of the conventional open type and the remote type. The remote type hot wire reactor has a separate glass chamber for hydrogen decomposition via the hot wire, and can supply atomic hydrogen to a substrate without significant radiation from the hot wire. Therefore, the atomic hydrogen density and substrate temperature can be independently controlled. Using the remote type setup together with the conventional open type setup, the authors demonstrated that the presence of atomic hydrogen in combination with substrate heating was necessary to completely remove SU-8. At a substrate temperature below 150 °C, the SU-8 removal rate was impractically small. In addition, after the apparent removal of SU-8 a white powder-like residue was found on the sample, which was identified with x-ray photoelectron spectroscopy as silicon components that originated from the silane coupling agent in SU-8. At a substrate temperature above 250 °C, on the other hand, SU-8 was thermally decomposed in a reduced pressure hydrogen environment, but the final state of the sample was an apparently carbonized film, that is likely owing to the insufficient fragmentation of SU-8 molecules in the absence of atomic hydrogen.