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14 September 2001 Photoresist thickness variation due to local and global topography
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The control of photoresist thickness and uniformity is becoming more crucial factor as the wafer size increases and the minimum feature size decreases since the variation of resist thickness could affect the critical dimension variation. In general, spin coating technique is used to coat photoresist on a wafer. To obtain the wet resist thickness profile around a topographical feature, the analytical solution derived from mass continuity and lubrication approximation was used. Under the same spin coating condition, the formations of distributed photoresist were different among the shape and size of topology. The final dried resist thickness profile was obtained by applying the resist thickness reduction due to evaporation during soft bake. The photoresist thickness and distribution on an isolated topology were compared with those of a periodic topology. In case of periodic topology, the photoresist thickness and distribution are dependent on topology density. The resultant thickness variations were applied to our simulation tool to determine the line width variations around the topological feature. We found that the difference in resist thickness due to topography could induce a severe line width variation. Mask bias or other correctional method is necessary to get the desired line width for the whole area around the topology.
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Jin-Young Kim, Heungin Bak, Young-Soo Sohn, Ilsin An, Kyoung-Yoon Bang, Hye-Keun Oh, and Woo-Sung Han "Photoresist thickness variation due to local and global topography", Proc. SPIE 4346, Optical Microlithography XIV, (14 September 2001);

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