Self-assembly and transferring of photoresist as planar layer for fabrication of TSV and free standing beams

This paper outlines a novel technique for using suspended photoresist above holes and trenches as planar bridge layer in the fabrication of through silicon vias (TSVs) and beams. Photoresist film is formed through self-assembly on water surface and then transferred to a wafer as planar bridge layer to cover previously fabricated holes and trenches, which can be patterned with photolithography. The suspension capability of the photoresist bridge layer increases with the film thickness. 300 to 500 nm thick photoresist films are able to be suspended on through-vias of up to 60 μm in diameter and 50 μm wide trenches. A novel process flow of TSV has been developed. TSVs of up to 60 μm in diameter have been fabricated, and the upper side of the TSVs is automatically planarized. Cu beams suspended above deep trenches have also been fabricated with the technique.