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17 May 2005 Real-time control of photoresist absorption coefficient uniformity
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Critical dimension (CD) or linewidth 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 absorption coefficient is one of the photoresist properties that can have an impact on the CD uniformity. The absorption coefficient determined the required exposure dose for printing the features. Hence, nonuniformity in absorption coefficient across the substrate will lead to nonuniformity in the linewidth. This paper presents an innovative approach to controlling the within wafer photoresist absorption coefficient uniformity. Previous works in the literature can only control the average uniformity of the absorption coefficient. Our approach uses an array of spectrometers positioned above a multizone bakeplate to monitor the absorption coefficient. The absorption coefficient 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 conventional proportional-integral (PI) control algorithm. We have experimentally obtained a repeatable improvement in the absorption coefficient uniformity from wafer-to-wafer and within wafer. A 50% improvement in absorption coefficient uniformity is achieved.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Arthur Tay, Weng-Khuen Ho, Xiaodong Wu, and Kuen-Yu Tsai "Real-time control of photoresist absorption coefficient uniformity", Proc. SPIE 5755, Data Analysis and Modeling for Process Control II, (17 May 2005);

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