Supercritical Fluid Deposition (SCFD) Technique as a Novel Tool for MEMS Fabrication

In the present paper, supercritical fluid deposition (SCFD) process is proposed for making functional films and coatings on the surface of MEMS devices. SCFD can provide superior step coverage on to high aspect ratio features at relatively low temperature. It also provides possibility to deposit wide variety of materials, including metals, oxides, and organic compounds, with controllability of substrate selectivity. For example, pure Cu was conformally dposited onto high aspect ratio vias for ULSI interconnects with 50 nm in diameter and 1 mum in depth at 220degC. The Cu-SCFD process is a selective process, which can deposit Cu film only on conductive surface, however, non-selective deposition of Cu is also possible by using CuMnOx as a buffer layer between Cu and insulative substrate. SiO₂ film was conformally fabricated in high aspect ratio trenches with 500 nm in width and 5 mum in depth at 200degC. Biocompatible poly ethylene glycol monomethacrylate (PEGMA) was grafted onto the surface of micro-channel with aspect ratio of 2500 at 80degC, and proved effective protection of protein adsorption onto SiO₂ surface.