In the fabrication of microelectronic and microelectromechanical systems (MEMS) devices, geometric patterns are transferred onto the Substrate by the process of lithography. A photoresist polymer is used in the process, which affects the Surface morphology, causing line-edge roughness (LER) and surface roughness (SR) in the transferred patterns. The performance of the resulting device is critically influenced by the LER and SR of the Surface. Various microscopy image analysis techniques are commonly used for LER and SR characterization, using metrics such as sigma, correlation length, and fractal dimension (FD). In this work, a mesoscale lattice Monte Carlo (MC) simulation is performed to model the photoresist system, Phase separation by spinodal decomposition is found as the Cause Of roughness. Multiresolution LER and SR characterization is performed on the model structure. The results complement the multiresolution LER characterization from image analysis and provide additional insight toward SR characterization, which is not feasible using two-dimensional SEM images.