Dry-film resist technology for versatile TSV fabrication for MEMS, tested on blind dummy TSVs

Three-dimensional (3D) integration of MEMS and ICs enables improvements in device performance, and often requires through-silicon vias (TSVs). TSV technologies presently available for micro electromechanical systems (MEMS) either have completely filled vias or hollow vias. Hollow vias imply perforated wafers, and limit further processing options. We have investigated dry film resist which enables photolithography on perforated wafers. The investigated resist was found to have adequate adhesion to silicon, SiO₂, and aluminum surfaces. Resist patterns with square openings of side length 15 μm and resist squares of side length 15 μm were reliably realized on all three investigated surfaces. On silicon surfaces, resist patterns with square openings of side length 10 μm and resist squares of side length 7 μm could be realized. The resist could withstand wet etching of 1 μm aluminum, reactive ion etching (RIE) of 7500 Å SiO₂ and deep silicon etching (DRIE) of 30 μm Si. Individual process steps for the future fabrication of DRIE etched TSVs with SiO₂ isolation, polysilicon conductor material and aluminum top contacts have been developed and verified.