Persistently shrinking design rules and increasing process complexity require tight control and monitoring of the exposure tool parameters [1, 2]. While control of exposure dose by means of resist single metric measurements is common and widely adopted. Focus assessment and monitoring are usually more difficult to achieve. A diffused method to determine process specific dose and focus conditions is based on plotting Bossung curves from single CD-SEM measurements and choosing the best focus setting to obtain the desired target CD with the widest useful window. With this approach there is no opportunity to build a data flow architecture that can enable continuous focus monitoring on nominal production wafers [3-5]. KLA-Tencor has developed a method to enable in-line monitoring of scanner focus on production wafers by measuring resist profile shapes on grating targets using scatterometry, and analyzing the information using AcuShapeTM and K-T AnalyzerTM software. This methodology is based on a fast and robust determination of best scanner focus by analyzing focus-exposure matrices (FEMs). This paper will demonstrate the KT CDFE and FEM Analysis methods and their application in production environment.
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