6 December 2004 Phase-shifting optical maskless lithography enabling ASICs at the 65- and 45-nm nodes
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An architecture for SLM-based mask writing and optical maskless lithography has been described in previous articles. This work reports on phase-shifting capabilities of different SLM's in light of rasterization and image stability. The tilting mirror SLM proven in the Micronic Sigma7300 mask writer has in other papers been presented as comparable to an attenuated phase-shift reticle. This article will feature the novel tilting phase-step mirror SLM. which has phase shifting capabilities enabling it to emulate hard phase-shift reticles. For a straight-forward rasterization architecture where individual pixels are determined by local pattern data it is required that the complex amplitude created by a mirror is confined to the real axis. This is the case for both the normal tilting mirror and the tilting phase-step mirror. For other micro-mirror designs this might not be true and in the case of the piston-mirror SLM this requirement leads to the demand that two or several mirrors work collectively, loosing degrees of freedom and resolution. The tilting phase-step mirror SLM provides a new rule-set for lithography: no penalty for phase shifting or aggressive OPC, seamless pattern decompositions, choice of optimal tones for each pattern, etc. This gives performance and flexibility not possible before.
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Tor Sandstrom, Ulric B. Ljungblad, "Phase-shifting optical maskless lithography enabling ASICs at the 65- and 45-nm nodes", Proc. SPIE 5567, 24th Annual BACUS Symposium on Photomask Technology, (6 December 2004); doi: 10.1117/12.569258; https://doi.org/10.1117/12.569258

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