Etch proximity correction by integrated model-based retargeting and OPC flow

Model-based Optical Proximity Correction (OPC) usually takes into consideration optical and resist process proximity effects. However, the etch bias proximity effect usually can not be completely eliminated by etch process optimization only and needs to be compensated for in OPC flow for several critical layers. Since the understanding of the etch process effect is getting better and accurate etch bias modeling is available now, lithographers start to migrate from rule-based correction to model-based correction. Conventionally when etch bias is considered in model-based correction, optical/resist/etch effect is corrected in one step by using the input layout as the final etch target. In this paper, we proposed a new flow in which etch and optical/resist process effect are separated in both model calibration and layout correction. This double separation allows easier control over etch and resist target, resulting in drastic reduction of OPC runtime. In addition it enables post-OPC verification at both resist and etch level. Advantages of the new integrated model-based retarget/OPC flow in RET implementation are also discussed.