Fabrication of fine metal microstructures packaged in the bonded glass substrates

In order to realize fine microstructures with high aspect ratio, two kind of thick-resist-based metal molding processes were studied. A novel technique obtaining fine line/space and high aspect ratio thick photoresist patterns on a glass substrate by the simple UV lithography was developed. A three-layer resist method using reactive ion etching (PIE) for patterning thick photoresist was also examined. The former method is to use fine thin metal patterns (<1 μm) formed on the glass substrate as the exposure mask. A thick negative photoresist is coated on it and UV light is iliuminated from the backside. Perfect contact between mask and photoresist is obtained and the influence of light diffraction is also avoided. By using SU-8 as the negative photoresist, minimum line/space of 1 μm and high aspect ratio of about 5 was achieved. The metal layer is served as a seed layer for Ni electroplating as well. Metal microstructures were also fabricated by the three-layer resist method using the thick photoresist-thin SiO₂-thin photoresist structure. Even an usual contact UV lithography was applied to pattern the thin photoresist layer and a usual CCP-RIE was used to etch the SiO₂ and thick photoresist layer, at least 1 μm gap microstructures were obtained by the Ni electroplating. Micro-packaging method using SiO₂-SiO₂ bonding with hydrofluoric acid was also studied. HF bonding has a remarkable feature that the bonding of quartz-to-quartz can be obtained at low temperature (<80 C). The bonding conditions suitable for micropackaging were examined under different HF concentration, pressure, and temperature. Reasonable bond strength equal to that by the anodic bonding is obtained under high-applied pressure during bonding. Packaging method is proposed using combination of the thick-resist-based molding and the HF bonding.