Advances in Fabrication of X-ray Masks based on Vitreous Carbon using a new UV sensitive positive Resist

LIGA is a well-established process to fabricate metallic micro parts with high resolution, high precision and very low sidewall roughness by means of X-ray lithography and electroplating. Typical mask substrate materials, e.g. beryllium, carbon based foils, Si3N4 or SiC show different disadvantages such as low X-ray transparency or high toxicity or high prices or low conductivity or high thermal expansion or surface porosity causing X-ray scattering. Due to the amorphous structure of vitreous carbon this mask material proved to significantly reduce the amount of side wall striations, leading to extremely smooth pattern sidewalls. For the fabrication of X-ray masks, PMMA with its unique features such as high aspect ratio patterns with high precision, exhibits low sensitivity and the layers preparation is not easy. SU-8, an epoxy-based UV and X-ray sensitive, chemically amplified negative tone photoresist exhibits high aspect ratio patterns with vertical sidewalls. The difficult remove of the resist after the electroplating process significantly hinders the inspection of the fabricated X-ray mask. We present the suitability of an UV sensitive, chemically amplified, aqueous-alkaline developable, and easy removable positive tone photoresist, XP mr-P 15 AV for the fabrication of X-ray masks by means of UV lithography on vitreous carbon substrates.