Through-Wafer Electrical Interconnects for MEMS Sensors

Abstract

Abstract The fabrication and characterization of p-type silicon electrical through-wafer interconnects (pETWI) on a silicon wafer is presented. Together with previously developed n-type ETWI [1], the pETWI enables complementary ETWI (CETWI) for maximum flexibility of through-wafer interconnects for MEMS sensors and semiconductor devices. Deep reactive ion etching using the Bosch process is employed to create high aspect ratio 20 μm vias through the wafer. The interconnects are electrically isolated from the bulk silicon substrate by a 2 μm thermal oxide layer. Electrical conduction is achieved by depositing several layers of boron-doped polysilicon. Details of the fabrication process as well as results of the pETWI characterization are presented. Interconnects with various polysilicon doping concentrations were fabricated to investigate the effect on the resistance, capacitance and noise. Average resistance values between 10 Ω and 14 Ω were obtained for each interconnect depending on the doping levels. This resistance is suitable for many MEMS applications. High frequency capacitance versus voltage (C-V) characteristics and the noise power spectral density (PSD) were also measured.