22 August 2001 Improving the measurement algorithm for alignment
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As semiconductor design rules decrease, tighter tolerances are required for alignment. Improvement of the measurement algorithm can make a considerable contribution to reduction of the overlay error. An algorithm makes the alignment accuracy greatly improved that utilizes wavelet transform and uses information about image asymmetry. Experimental result using the Alignment Data Logging System shows that there is a process that the algorithm reduces the overlay error from over 100nm (3(sigma) ) to under 50nm. Two other algorithms are also introduced that are an interpolation method that reduces error from image sampling and a mark recognition method that reduces measurement failures focusing on some kinds of symmetry of the alignment mark.
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Shinichi Nakajima, Shinichi Nakajima, Yuho Kanaya, Yuho Kanaya, Akira Takahashi, Akira Takahashi, Koji Yoshida, Koji Yoshida, Hideo Mizutani, Hideo Mizutani, } "Improving the measurement algorithm for alignment", Proc. SPIE 4344, Metrology, Inspection, and Process Control for Microlithography XV, (22 August 2001); doi: 10.1117/12.436780; https://doi.org/10.1117/12.436780

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