Compatibility of CO gas sensitive SnO₂/Pt thin film with silicon integrated circuit processing

In this paper, we discuss the integration problems associated with tin dioxide thin film to meet the requirement of silicon IC processing. Since aluminum is being used as interconnection metal lines in various IC devices, the post annealing of tin dioxide thin film cannot be performed at high temperatures. At higher annealing temperature, the aluminum diffuses into the silicon and forms a metal alloy, which reduces the performance of the device. To overcome this problem, we propose an annealing process for the tin dioxide thin film at 450°C in oxygen ambience for shorter time (15 min) and then quenching at room temperature. The performance, such as sensitivity and response time of the quenched device, is better than that of the device cooled at 50°C/h. Sensor measurements were performed at 150-300°C at 400-1000 ppm CO gas concentration, and stability of the devices was measured up to 720 h. The device was stable during long operation hours. Hydrogen gas was used to investigate the selectivity of the device. The response indicated that the quenched device was selective towards CO gas. The response of the quenched device was quite different towards CO and hydrogen gas. The morphology of the devices was investigated using SEM.