Ultra-thin chip technology for system-in-foil applications

A new additive ultra-thin chip fabrication process is presented, utilizing an array of vertical anchors that mechanically connect silicon membrane chips to a standard silicon wafer. The process is demonstrated down to 8 µm silicon chip thickness, with a chip thickness control better than ±0.2 µm and a surface topography with average roughness < 7 nm. Such pre-processed wafers can be used for CMOS manufacturing like any conventional silicon substrate. A wide process window with yield figures exceeding 99% is achieved by proper management of the built-in and externally applied stress on the anchors. The excellent mechanical flexibility and stability of these ultra-thin chips make them particularly suitable for system-in-foil applications.