In situ measurement of wafer temperature using two sensors with different dynamical properties

Abstract

As more and more features are packed onto smaller silicon chips, there is a need to optimize wafer fabrication process conditions to the fullest. Closed-loop control is one approach for meeting the rising need for more stringent control over the absolute and spatial temperature of wafers undergoing the post-exposure bake (PEB) process. For an automatic control loop to be implemented successfully, the feedback signals must be accurate and reliable. However, in situ temperature measurement systems based on either contact or non-contact sensors cannot achieve the required accuracy. Another challenge is to measure the wafer temperature without disrupting the manufacturing process. In this paper, a non-intrusive method that uses the readings from two contact sensors and the recursive least-squares algorithm to estimate the sensor model is described. When the sensor model is identified, the inverse model method is applied to achieve fast and accurate temperature measurements. Experimental results demonstrate that the algorithm is able to provide accurate real-time temperature measurement, which may be used as the feedback signal to achieve closed-loop control.