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28 March 2017 The new OPC method for obtaining the stability of MBAF OPC
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Current patterning technology for manufacturing memory devices is being developed towards enabling high density and high resolution capability. However, as applying high resolution technology results in decreased process margin, OPC has to compensate for such effect. Since the process margin is decreased greatly for contact layers, technologies such as RBAF (Rule-Based Assist Feature), MBAF (Model-Based Assist Feature), and ILT (Inverse Lithography Technology) are considered to maximize the process margin [1, 2, 3]. Although ILT is the best solution in terms of process margin, it has several disadvantages such as long OPC run-time, mask complexity, and unstable mask fidelity. MBAF method is a good compromise for more advanced techniques mitigating those risks (but not eliminating it), which is why it is often used for contact layers.

When setting up the rules for RBAF, not all patterns are considered. Thus, applying RBAF for contact layers may result in decreased process margin for certain patterns since the same rule is applied globally. MBAF, on the other hand, can maximize the process margin for various patterns as it generates AF (Assist Feature) to locations that maximize the margin for the patterns considered. However, MBAF method is very sensitive to even a slight change of a target, which influences the locations of the AF. This leads to generating different OPCed CD of the main features, even for those that should not be affected by the changed target. Once the OPCed CD is changed, it is impossible to obtain the same mask CD even when the mask is manufactured with the same method. If this case occurs during mass production, the entire layer needs to be confirmed after each revision which leads to unnecessary time loss.

In this paper, we suggest a new OPC method to prevent this issue. With this flow, OPCed shapes of unchanged patterns remain the same while only the changed targets are OPCed and replaced into the corresponding location, while the boundaries between those regions are corrected using a model based boundary healing. This method can reduce the overall OPCTAT as well as the time spent in verifying the entire layout after each revision. Details of these results will be described in this paper. After further studies, this flow can also be applied to ILT.
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Jookyoung Song, Jaeseung Choi, Chanha Park, Hyunjo Yang, Daekwon Kang, Minsu Oh, Manjae Park, James Moon, Jun Ye, and Stanislas Baron "The new OPC method for obtaining the stability of MBAF OPC", Proc. SPIE 10148, Design-Process-Technology Co-optimization for Manufacturability XI, 1014813 (28 March 2017);


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