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29 April 2004 Complementary feed-forward and feedback method for improved critical dimension control
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In modern day semiconductor manufacturing, control of patterned line widths is an especially important task as even the smallest deviation from desired critical dimension (CD) target could result in undesirable electrical results. Traditional methods of CD control have included a feedback component where dose is adjusted through time, based on the measured critical dimensions of previous lots. Depending on process setup, stack influence on patterned features can often be diminished by introduction of organic anti-reflection coating (ARC) prior to the application of photoresist. Unfortunately even with an ARC layer, due to extreme topography and film stack, CD influences may be pronounced. Most often any such CD influence is exhibited as a Lot-2-Lot (L2L) component of variation and to a lesser degree as a Wafer-2-Wafer (W2W) component. A simple feedback system can be adjusted to encompass a larger number of lots for dose recommendations thus making certain to include closer to the entire population of stack variation. An improved control system is one in which this feedback component is supplemented by a feed-forward component where a certain stack predictor is used in providing a specific recommendation for a lot. Stack information for a lithographic layer used in DRAM manufacturing will be presented alongside with a relationship existing between critical dimensions of features patterned in photoresist and top film thickness. Significant economic rework cost reduction and improvement in CD control with a two-month implementation of a complementary feed-forward and feedback system will be compared against performance with the feedback only system.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Igor Jekauc, Christopher J. Gould, Walter Hartner, and Tim Urenda "Complementary feed-forward and feedback method for improved critical dimension control", Proc. SPIE 5378, Data Analysis and Modeling for Process Control, (29 April 2004);

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