Combinatorial multi-level mold inserts using micro machining and X-ray lithography

The present technology advancement in biomedical, micro-electro-mechanical systems (MEMS) engineering, bio-MEMS, healthcare, etc. is driving the need to fabricate devices with multi-level, high aspect ratio and complex microstructures, which in turn requires high quality mold inserts with all these features. The present thesis is concentrated in fabricating a multi-level mold insert with complex quasi 3 dimensional micro structures with dimensions down to 10µm and aspect ratios greater than 30 using a process combination of micro milling with X-ray lithography. Therefore, in this study the main focus was to fabricate a high quality mold insert template, which can be electroplated to obtain a mold insert. A suitable substrate, copper, was first selected for the blank from the available choices of materials. Further, to improve the adhesion of copper to the resist, different surface modifications were employed. The results showed that oxidation of copper gave the optimal surface for excellent adhesion to resist. In order to expose structures at multi-level, two different exposure methods to obtain equal bottom dose (counter replica structures and aperture exposures) were explored. Two exposure methods showed similar results in terms of patterning quality and retaining high aspect ratio microstructures. Finally, fabricated template was electroplated with nickel to demonstrate the feasibility of producing a multi-leveled mold insert with complex, high aspect ratio microstructures