24 March 2017 Reticle heating feed-forward control (RHC2) on NXT:1980Di immersion scanner for enhanced on-product overlay
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Abstract
Scanners in High-Volume-Manufacturing conditions will experience a large range of reticles that vary in reticle transmission and reticle diffraction characteristics. Especially under full production loads reticles will heat up due to the exposure light-load and as such experience thermo-mechanical deformations. The resulting reticle pattern distortion can be partially translated in a deteriorated overall system overlay. Due to the geometry of the reticle and exposure fields, these reticle thermal effects are in general barrel-shape distortions that can be well corrected with the available set of lens manipulators. Nevertheless node-over-node the residual overlay errors associated with thermo-mechanical reticle deformation needs further reduction since it contributes to the total onproduct overlay performance. To reduce overlay caused by reticle temperature drift, NXT1980Di includes an active cooling mechanism suppressing the reticle temperature changes during exposure significantly. Even though the reticle temperature excursions are well suppressed, residual intra-wafer overlay drift effect can still be observed. Before exposure of a wafer, reticle deformation is measured during reticle align using in-line alignment / image sensors (TIS or PARIS). This is enabled by adding alignment markers around the circumference of the image field on the reticle. The measured reticle deformations are then fed to the system control network and dynamically corrected for by making use of the available manipulators in the scanner and the projection lens. Wafer-by-wafer reticle distortion measurements are performed to accurately capture the transient dynamics present in reticle heating during normal production lots. A new version of Reticle Heating Feed-forward Control (RHC2) is introduced that uses reticle-heating-induced deformation measurements over time and exposure sequence information to calibrate reticle-deformation-predictionmodels. These models are based on thermo-mechanical models that simulate reticle deformation under various exposure conditions and are applied in-line to the exposures to reduce intra-wafer overlay drift effects.
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Young Ha Kim, Young Ha Kim, Jonghoon Jang, Jonghoon Jang, Byeong Soo Lee, Byeong Soo Lee, Hyunwoo Hwang, Hyunwoo Hwang, Youngsun Nam, Youngsun Nam, Jeong-Heung Kong, Jeong-Heung Kong, Young Seog Kang, Young Seog Kang, Se-Yeon Jang, Se-Yeon Jang, Bart Paarhuis, Bart Paarhuis, Jeroen van der Wielen, Jeroen van der Wielen, Barry Moest, Barry Moest, Joris Jongen, Joris Jongen, Stefan Weichselbaum, Stefan Weichselbaum, Niek Verbeek, Niek Verbeek, Marco Stavenga, Marco Stavenga, Roelof de Graaf, Roelof de Graaf, Richard Droste, Richard Droste, } "Reticle heating feed-forward control (RHC2) on NXT:1980Di immersion scanner for enhanced on-product overlay", Proc. SPIE 10147, Optical Microlithography XXX, 1014717 (24 March 2017); doi: 10.1117/12.2259792; https://doi.org/10.1117/12.2259792
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