28 May 2004 TTR (through the reticle) alignment system with photoresist ablation technique
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Various alignment methods for a semiconductor exposure tool have been proposed and developed. Especially, the TTR (through the reticle) alignment technique has been expected as the ideal system since the direct measure between a reticle and a wafer through the projection lens has no baseline error. However, it requires that an alignment illumination be a single wavelength of the exposure light because of the chromatic aberration of the projection lens. The strong absorption by the resist and the BARC (bottom anti reflective coating) weakens the alignment signal intensity, and the interference fringe in the resist by the single wavelength sacrifices the precise position detection. Such difficulty in signal detection has blocked the TTR system from becoming realized. We tried to address this problem by peeling the resist and BARC on alignment marks. To peel the resist and BARC, we performed elective ablation using a laser ablation method with the Q-switch Nd YAG laser. The laser-ablated alignment marks on some process wafers were measured by the TTR alignment system. The signal waves with enough contrast were measured over all wafers and the satisfied alignment accuracy was examined.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ryo Tanaka, Ryo Tanaka, Mitsuru Kobayashi, Mitsuru Kobayashi, Masahiko Yasuda, Masahiko Yasuda, Nobutaka Magome, Nobutaka Magome, Kazuhiko Ishigo, Kazuhiko Ishigo, Hiroshi Ikegami, Hiroshi Ikegami, Tatsuhiko Higashiki, Tatsuhiko Higashiki, "TTR (through the reticle) alignment system with photoresist ablation technique", Proc. SPIE 5377, Optical Microlithography XVII, (28 May 2004); doi: 10.1117/12.544231; https://doi.org/10.1117/12.544231

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