| The design and fabrication of a microscale shear force sensor for use in Chemical Mechanical Polishing (CMP) is presented. This sensor is intended to sense local scale shear forces induced by contact between surface features on a silicon wafer and asperities on a polishing pad. This sensor was designed using mask layout techniques and simulated using a lumped element model. This model predicted the dynamic response of the sensor to a frequency domain input. The sensor was fabricated using bulk micromachining and the bonded lost wafer process. In this process features are etched into the surface of a Silicon On Insulator (SOI) wafer. The SOI wafer is then bonded to a glass wafer using a technique known as anodic bonding. Next, the majority of the SOI wafer is dissolved using chemical etchants, and a second etch releases the sensor elements from a layer of silicon dioxide. The sensors did not survive the fabrication process. Failure modes included incomplete bonding, difficulties with a through wafer wet etch using potassium hydroxide and failure of devices caused by pressure differences induced during wafer bonding. Failure modes as well as recommendations for resolution are presented in full detail. Electromechanical test data for a similar sensor was obtained to demonstrate the applicability of the modeling and characterization procedures. |
