Characterization of the DRIE Process for ETWI for Piezoresistive Inertial Sensors

Electrical through-wafer interconnects (ETWI) are often integrated with inertial sensors for harsh liquid environment applications. Devices with metal interconnects are very susceptible to corrosion in aquatic environments. An alternative approach is to form highly doped, conductive polysilicon through the wafer from the back side (unexposed to harsh environments) to the front side of the device’s chip. ETWI technology requires etching through the wafer. This places a high demand on the through wafer etch profile, critical dimension control, and feature size dependent etch rate (etch lag). On test structures, we measured the sidewall profile and etch rate as a function of several etch parameters (etch cycle time, platen power, current power, C4F8 flow, etc). In addition, we assessed practical methodologies for handling the wafer during the etch. The objective of this project is to use statistical design of experiment (DoE) to optimize the deep reactive ion etch (RIE) recipe for through wafer etching and test wafer bonding for through wafer via formation. From the development of electrical through wafer interconnects, more reliable sensor devices can be fabricated for studies in hydrodynamics in harsh environments in addition to a plethora of other applications.