Process development and characteristic evaluation of micro-bolometer device

Based on MEMS micro-bridge structure, micro-bolometer device was developed on standard semiconductor production line. Chemical Vapor Deposition (CVD) technology was used to deposit amorphous silicon (α-Si) film as sensing material. The within wafer thickness uniformity and the resistance uniformity of 1000 Å α-Si film can be controlled to be less than 2%, and the Temperature Coefficient of Resistance (TCR) of 1000 Å α-Si film can reach at about −2.5%. Contact module of MEMS micro-bridge structure was developed by trench first approach, and electrical connection between MEMS and readout circuit was achieved by thin electrode layer on sidewall and bottom of the anchor and contact structure. Ti/TiN thin metal layer was used as electrode layer, and sensing resistor device was defined by the electrode layer patterns. Sensing material resistor device was fabricated by optimized integration scheme, which can achieve better process control on the sensing material loss and electrical layer sidewall recess etch amount. After device fabrication, room temperature resistance of device was about 250 kΩ with good ohmic contact. Device level TCR was measured at about −2%, and slightly lower than the data of thin film on blanket wafer. And the resistance data during the temperature raising up and down indicated that there was no hysteresis effect. Finally the MEMS device was released, and the optical and SEM data showed good physical performance, which can match the technical requirements of micro-bolometer production.