A Novel Batch Production Technique of Metal Embedded Thin Film Microsensors for Applications in Manufacturing

Effective monitoring and diagnosis of manufacturing processes is of importance in reducing operation costs, improving product quality, and reducing process time. If conditions of manufacturing tools are continuously monitored, problems can be detected and solved during the processing cycle, resulting in less tool damage, higher productivity, and less energy consumption. In-situ monitoring of the basic operating conditions (e.g. temperature and strain) of certain mechanical tools and components can be accomplished by placing microsensors in some critical locations. Thin film microsensors (e.g. thermocouple, strain gauge) have drawn considerable attention recently due to their small size, fast response and lower cost [1]. Since most tools and components in manufacturing process are metallic, metal embedded thin film microsensors are very attractive. A new batch fabrication technique based on electroplating and wet chemical etching of silicon has been developed. Microsensors were directly fabricated on an etch stop layer grown on silicon wafer. A multilayer dielectric is deposited to insulate sensor areas followed by seed layer deposition, and electroplating a thicker metal layer. After silicon wafer is etched out, the microsensors are transferred from silicon to electroplated metal substrate directly. After plasma etching of the etch stop layer, these sensors can be further embedded into another electroplated metal layer from the top after insulation by dielectric multilayer. Metal embedded strain gauge array was fabricated successfully. Thin film Ni/Cr strain gauges were fabricated on LPCVD silicon nitride layer grown on a 3-inch silicon wafer. Each strain gauge unit was insulated by Al₂O₃/PECVD Si_xNy/Al₂O₃ multilayer before seed layer deposition and electroplating a thick nickel layer on whole wafer. Si wafer was then etched out in KOH solution to transfer all microsensors to electroplated nickel layer. LPCVD nitride layer covering the sensors was dry etched and same multilayer dielectric was selectively deposited over the sensors except pad areas. These microsensors were finally embedded into another electroplated nickel layer leaving the pads uncovered for external connection. This process offers a novel way to realize batch production of metal embedded microsensors for use in hostile manufacturing environment.