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1 April 2010 Focus and dose deconvolution technique for improved CD control of immersion clusters
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As critical dimension (CD) control requirements increase and process windows decrease, it is now of even higher importance to be able to determine and separate the sources of CD error in an immersion cluster, in order to correct for them. It has already been reported that the CD error contributors can be attributed to two primary lithographic parameters: effective dose and focus. In this paper, we demonstrate a method to extract effective dose and focus, based on diffraction based optical metrology (scatterometry). A physical model is used to describe the CD variations of a target with controlled focus and dose offsets. This calibrated model enables the extraction of effective dose and focus fingerprints across wafer and across scanner exposure field. We will show how to optimize the target design and the process conditions, in order to achieve an accurate and precise de-convolution over a larger range of focus and dose than the expected variation of the cluster. This technique is implemented on an ASML XT:1900Gi scanner interfaced with a Sokudo RF3S track. The systematic focus and dose fingerprints obtained by this de-convolution technique enable identification of the specific contributions of the track, scanner and reticle. Finally, specific corrections are applied to compensate for these systematic CD variations and a significant improvement in CD uniformity is demonstrated.
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Anne-Laure Charley, Koen D'havé, Philippe Leray, David Laidler, Shaunee Cheng, Mircea Dusa, Paul Hinnen, and Peter Vanoppen "Focus and dose deconvolution technique for improved CD control of immersion clusters", Proc. SPIE 7638, Metrology, Inspection, and Process Control for Microlithography XXIV, 763808 (1 April 2010);

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