Real-time spatial control of photoresist development rate

Abstract

Critical dimension (CD) is one the most critical variable in the lithography process with the most direct impact on the device speed and performance of integrated circuit. The development rate can have an impact on the CD uniformity from wafer-to-wafer and within-wafer. Conventional approaches to controlling this process include monitoring the end-point of the develop process and adjusting the development time or concentration from wafer-to-wafer or run-to-run. This paper presents an innovative approach to control the development rate in real-time by monitoring the photoresist thickness. Our approach uses an array of spectrometers positioned above a programmable bakeplate to monitor the resist thickness. The develop process and post-development bake process is integrated into one equipment. The resist thickness can be extracted from the spectrometers data using standard optimization algorithms. With these in-situ measurements, the temperature profile of the bakeplate is controlled in real-time by manipulating the heater power distribution using a control algorithm. We have experimentally obtained a repeatable improvement in controlling the end-point of the develop process from wafer-to-wafer and within wafer.