Mems as Temperature Sensors During High Temperature Processing

AbstractIn high temperature processing of microelectronics such as rapid thermal processing (RTP), an accurate measurement of temperature is critical in fabricating defect-free devices. Currently, temperatures during such processes are measured using thermocouples or pyrometers. However, accurate measurements with thermocouples are troublesome due to the difficulties in holding the thermocouples in place and maintaining good thermal contact. A further drawback for thermocouples is that they are highly intrusive. For pyrometers, optical interference effects and partial transparency limit their applicability and the local temperature of wafers near the electronic devices are difficult to measure using pyrometer due to relatively large spot size. Microelectromechanical systems (MEMS) technology is being used in developing innovative temperature sensor (T-MEMS), which allow an ex-situ examination of the maximum temperature reached during a thermal process by creating a permanent change in structure at high temperatures. The performance of the device relies on the thermophysical properties of the materials; specifically, the Young's modulus, thermal expansion coefficient, and the ultimate strength must be considered for silicon, and silicon nitride. Through careful experimental design and accurate modeling of their structural behavior, the high-temperature material properties can be determined using the T-MEMS and calibrated furnaces.