Results of feature profile evolution modeling of a STT-MRAM (Spin Transfer Torque - Magnetoresistive Random Access Memory) etch process will be discussed. STT-MRAM is a promising candidate for future memory. This non-volatile RAM has fast read/write, is scalable to DRAM (dynamic random access memory) cell sizes, has low power, and has possible multi-bit multi-level capability. This talk will address modeling the pattern definition of the MTJ (magnetic tunneling junction) stack through an etch process. The feature model used for the study is a 3D Monte Carlo model. The MTJ stack consists of many metals which are not easily etched (i.e., mostly non-volatile etch by-products) such as CoPt, Ru, CoFeB, and MgO. Thus, the feature model assumes mostly physical sputtering as the etch mechanism. The material emission model is also important in a physically dominated etch process. The impact of different material emission models on the final profile will be discussed. The main issue is removal of metal sidewall deposits which are the result of the re-deposition of the sputtered MTJ layers. The thickness of the re-deposited metal on the sidewall decreases from bottom to top. The closer the sidewall is to the sputter source at the feature bottom the thicker the deposit. The thickness is also heavily influenced by the geometry of the mask. Given the physical nature of the etch line-of-sight of incoming ions and outgoing metal is important. Negative sidewall slopes can also influence the morphology of the re-deposited metal. The square shaped pillar patterns modeled have non-uniform deposit around the circumference of the feature with larger metal at the corners. The etch front is also more non-uniform due to the length difference from corner to corner vs side to side for the features. Smaller aspect ratio features will allow removal of more MTJ metal but may have less of an impact on the final CDat the MgO layer. Material sputter emission models which are more focused lead to thicker deposits in sputtered layers, spottier deposits on patterned sidewalls, and ledge formation. The difficulty in removing the metal sidewall deposits leads to strategies such as the use of off-angle ion beams. Off-angle ion beams take advantage of the off-angle peaks in the ion yield curves. The number of steps per rotation and the off-angle value influence the final profile. Fewer steps / rotation lead to more non-uniform etch fronts. Larger off-angles lead to larger yield numbers for the sidewall deposited metal but will also be shadowed by nearby features limiting the depth where the metal removal takes place.