Investigation on LIGA-like process based on multilevel imprint lithography

A low-cost quasi-LIGA process is proposed, in which, instead of using thick resist technique, micro-structure with large structural height is achieved by multilevel imprinting and through-mask plating. To achieve precise alignment between individual layers, an alignment system based on computer micro-vision is developed and the experimental results show an average overlay accuracy within 1.5 μm with a standard deviation within 0.33 μm. Good adherence of resist on seed layer is achieved by substrate surface oxidation and using a coupling agent, which establishes a chemical bond between substrate surface and the resist layer. The deposit uniformity is improved by electroplating process optimization to enhance the cathode polarization. Through electrolyze etching on previous layer before next level of metal deposition, the fresh metal surface is obtained and the bonding strength between adjacent metal layers is enhanced. With the developed process, tri-layer photoresist and metallic structures with a pattern feature size of 20 μm were successfully fabricated.