17 December 2003 Beyond k1=0.25 lithography: 70-nm L/S patterning using KrF scanners
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Abstract
The extendibility of optical lithography using KrF and ArF exposure tools is still being investigated, even, being demanded strongly now, due to the unforeseen issues, high cost, and general difficulty of NGLs - including F2 and immersion lithography. In spite of these challenges Moore's Law requires continued shrinks and the ITRS roadmap still keeps its aggressive timetable. In order to follow the ITRS roadmap, the resolution must keep improving by increasing the lens NA for optical exposure tools. However, the conventional limit of optical resolution (kpitch=0.5) is very close for the current technologies, perhaps limiting progress unless NGL becomes available quickly. Therefore we need to find a way to overcome this seemingly fundamental limit of optical resolution. In this paper, we propose two practical two-mask /double-exposure schemes for doubling resolution in future lithography. One method uses a Si-containing bi-layer resist, and the other method uses Applied Materials' APF (a removable hard mask). The basic ideas of both methods are similar: The first exposure forms 1:3 ratio L/S patterns in one resist/hard mask layer, then the second exposure images another 1:3 ratio L/S pattern in-between the two lines (or two spaces) formed by the first exposure. The combination of these two exposures can form, in theory, kpitch=0.25 patterns. In this paper, we will demonstrate 70nm L/S pattern (140nm pitch) or smaller by using a NA0.68 KrF Scanner and a strong-RET reticle, which corresponds to kpitch = 0.38 (k1=0.19). We will also investigate the critical alignment and CD control issues for these two-mask/dual-exposure schemes.
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Takeaki Ebihara, Takeaki Ebihara, Marc David Levenson, Marc David Levenson, Wei Liu, Wei Liu, Jim He, Jim He, Wendy Yeh, Wendy Yeh, Sang Ahn, Sang Ahn, Toshihiro Oga, Toshihiro Oga, Meihua Shen, Meihua Shen, Hichem M'saad, Hichem M'saad, } "Beyond k1=0.25 lithography: 70-nm L/S patterning using KrF scanners", Proc. SPIE 5256, 23rd Annual BACUS Symposium on Photomask Technology, (17 December 2003); doi: 10.1117/12.518104; https://doi.org/10.1117/12.518104
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