The microfabrication of thick electroforming micro moulds using a KMPR negative tone photoresist has been investigated. SU-8 resist is currently the most widely used thick resist for electroforming masking, but difficulties in removing crosslinked SU-8 have considerably limited its applications in microelectroforming applications. KMPR resist is a complement to SU-8 in providing electroforming moulds. A considerable advantage of KMPR compared to SU-8 is that it can easily be removed after completion of electroforming using commercially available chemical removers. In the characterization of KMPR for making microelectroforming moulds, an optimized double spin lithography process using an UV mask aligner has been developed. The process enables the KMPR moulds to have dimensional accuracy and sidewall verticality comparable to those of SU-8. Structures of 180 µm in thickness and aspect ratio of 18:1 have been fabricated repeatedly in experiments. Microelectroforming was conducted in the KMPR moulds and the results show excellent geometry. The KMPR moulds were easily stripped without damaging the metal components or leaving residues around the metal structures. KMPR resist was also successfully stripped from confined areas, such as nickel channels of 180 µm thickness and 40 µm width.
This paper presents the effects of BCl 3 additive gas on physical damage and the prevention against damage in oxide hard-mask-based Al etching. The BCl 3 addition in the TiN/Ti break-through step effectively passivated the sidewall against the upper TiN/Ti notching damage; however, the TiN/Ti profile was easily distorted under excessive BCl 3 added. The Al bottom notching depth decreased with decreasing BCl 3 /Cl 2 ratio in the Al over-etch step. As the BCl 3 /Cl 2 ratio is less than or equal to 0.625, the Al bottom notching was eliminated. Nevertheless, the low BCl 3 addition in the Al over-etch step would result in increasing Al residues because insufficient passivation at low BCl 3 flow cannot effectively protect the semi-iso Al sidewall from attack of Cl atoms, and insufficient ion bombardment at this low BCl 3 cannot remove those residues around the damaged sidewall. An optimized condition achieves both notching-free and residue-free profiles.
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