Ivo Rudolph

Generation and Characterization of Super-Hydrophobic Micro- and Nano-structured Surfaces

Here we describe the use of a backside exposure method for the creation of high aspect ratio tapered microstructures with nano-porous sidewalls. These sidewalls result from the exposure and curing conditions of the SU8 matrix. The structures show ultra-hydrophobic behavior with water contact angles of more than 160°, without an additional coating of the SU8 polymer. By choosing appropriate exposure conditions, needlelike structures can be created with a high level of porosity, covering their entire surface. The contact angle hysteresis values of such structures lie in the range of 20°. After an additional deposition of smooth and thin metallic gold film and coating it with an alkyl thiol selfassembled monolayer (SAM), we were able to decrease this hysteresis to values of around 10°. By using thin and rough metallic films like wet chemically oxidized titanium oxide and a fluoralkylsilane SAM, the hysteresis values could be reduced to only 4°.

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.