Study of model based etch bias retarget for OPC

Model based Optical proximity correction is usually used to compensate for the pattern distortion during the microlithography process. Currently, almost all the lithography effects, such as the proximity effects from the limited NA, the 3D mask effects due to the shrinking critical dimension, the photo resist effects, and some other well known physical process, can all be well considered into modeling with the OPC algorithm. However, the micro-lithography is not the final step of the pattern transformation procedure from the mask to the wafer. The etch process is also a very important stage. It is well known that till now, the etch process still can't be well explained by physics theory. As we all know, the final critical dimension is decided by both the lithography and the etch process. If the etch bias, which is the difference between the post development CD and the post etch CD, is a constant value, it will be simple to control the final CD. But unfortunately this is always not the case. For advanced technology nodes with shrinking critical dimension, the etch loading effect is the dominate factor that impacts the final CD control. And some people tried to use the etch-based model to do optical proximity correction, but one drawback is the efficiency of the OPC running will be hurt. In this paper, we will demonstrate our study on the model based etch bias retarget for OPC.