The model accuracy for Optical Proximity Correction (OPC) and Inverse Lithography Technology (ILT) applications is a critical factor for patterning success in advanced technology nodes. One difficult challenge has been the accurate and fast simulation of Negative Tone Development (NTD) photoresist processes. It has been widely observed that CD measurements, top-down SEM contour images and X-section or AFM resist side wall profile measurements cannot be adequately predicted by conventional lithography process models, e.g., . Therefore, conventional OPC models were often unable to meet the demanding accuracy requirements of advanced logic or memory manufacturing. A key to achieving the demanding model accuracy requirements in NTD photoresist processes is to consider the photoresist shrinkage effects both in the Post-Exposure-Bake (PEB) step and photoresist development process step. Starting from continuum elastic mechanics, e.g., , we have developed a fast and accurate full 3D compact shrinkage model and validated its accuracy and usefulness vs. experimental results for several advanced processes and vs. rigorous simulation using a full physical lattice model. The compact model captures the significant photoresist shrinkage and deformation behaviors such as surface topography, resist sidewall angle (SWA) and layout pattern dependency , with much faster runtime capable of use in OPC and ILT mask data optimization. The speed and flexibility of the model are such that it can also be applied to help increase accuracy of simulation for some complex physical behaviors seen in other photoresist processes such as EUV and positive tone develop (PTD) photoresist.