Design of fabrication process of a thermal contact sensor for surface defect inspection

A fabrication process of a contact detection sensor, which is thermally-sensitive thin film sensor referred to as a thermal contact sensor to be used for a surface defect inspection, is designed based on photolithography process. The existence of a small defect, the size of which is on the order of several-ten nanometers, would be detected by capturing frictional heat generated at the contact between the thermal contact sensor and the defect. The thermal contact sensor is therefore designed to detect small quantity of frictional heat, the rate of heat supply of which is estimated to be on the order of microwatts. In this paper, followed by the fabrication of the first prototype thermal contact sensor in the previous study, the structure of the thermal contact sensor is modified to make the thermally-sensitive area of the thermal contact sensor to be located at its top surface. For further stable fabrication of a thermal contact sensor, lift-off process with a positive resist is also introduced in the sensor fabrication process. Experiments are carried out to verify the feasibility of the fabricated second prototype thermal contact sensor. In addition, aiming to improve sensitivity of the thermal contact sensor, the relationship between the sensor sensitivity and the sensor bias voltage is investigated in experiments. Furthermore, FEM simulation is carried out to estimate the increase of the sensor temperature due to a self-heating effect by the bias voltage applied to the thermal contact sensor, since the sensor temperature deviation could affect the sensitivity of the thermal contact sensor.