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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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Optical proximity correction
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