Multiple Through-Wafer Interconnects for Stacking of Microsystems

Abstract

This paper describes a novel technology for multiple wafer frontside to backside interconnects, which has been applied to a multifunctional interconnect layer for an integrated microphone for hearing aid applications. Besides the interconnect layer with relatively large through-holes the stack consists of the microphone itself and an integrated circuit chip for signal conditioning. The patterning of the metallization on the interconnect wafer has been done using electrodepositable photoresist as mold for electroplating of a variety of metals. For the interconnect metallization we use copper. The bonding pads on the microphone side of the interconnect layer have been provided with under bump metallizations (UBM) and solder bumps. The IC side features a top surface metallization (TSM) suitable for conductive adhesive bonding. The realized feedthrough wires show good electrical performance in terms of low series resistance (100 mΩ) and small parasitic capacitance (< 1 pF).