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22 August 2001 Lens-heating-induced focus drift of I-line step and scan: correction and control in a manufacturing environment
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The lens heating (LH) induced focus drift of the ASML i-line Step & Scan was measured at five NA/Sigma settings: three ASML default and two TSMC production settings. The new LH scaling constants at three ASML settings, when multiplied by a dose-matching factor for production, agreed well with the default constants. Experimental results at NAI11 of 0.21 - 0.228 indicate that the LH induced focus drift is NA dependent, and the extent is NA = 0.4A ~ 0.5B>0.63 - 0.65. At the TSMC production settings of NA = 0.4A and 0.5B, the focus drift is approximately 20% greater than those predicted by the ASML LH algorithm. This study applies the new set of scaling constants for the LH focus correction. Long-term focus stability can be maintained within three standard deviations of less than 70nm, for all i-line Step & Scans in the manufacturing environment of one TSMC Fab.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Grace H. Ho, Anthony Cheng, Chung-Jen Chen, C. K. Fang, Meng C. Li, I-Chung Chang, P. T. Chu, Y. C. Chu, K. Y. Shu, C. Y. Huang, H. L. Yeh, H. C. Shiao, and Ho Ku Lan "Lens-heating-induced focus drift of I-line step and scan: correction and control in a manufacturing environment", Proc. SPIE 4344, Metrology, Inspection, and Process Control for Microlithography XV, (22 August 2001);

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