Molecular dynamics simulation of the early stage of the development process of negative-type nonchemically amplified resist in electron-beam lithography

With the advance of lithography technology, the fabricated pattern sizes have become comparable to the molecular scale of resist materials, making molecular behavior a critical factor in pattern formation. During the development process, phenomena such as resist molecule removal, molecular flow, and developer molecule infiltration strongly affect pattern profiles. Molecular-level simulations are useful for predicting and analyzing pattern formation. In this study, we performed molecular dynamics (MD) simulations to analyze the molecular behavior during the development process in electron-beam lithography, incorporating interactions between resist and developer molecules. The resist material was poly(glycidyl methacrylate) (PGMA), a negative-type nonchemically amplified resist. The DREIDING potential was employed for simulations. In the electron exposure simulation, structural change of PGMA was introduced as cross-linking between resist molecules in the exposed region. In the development simulation, developer molecules were placed on the electron-exposed PGMA resist structure and the structural relaxation process was simulated. The molecular behavior in the early stage of development in the electron-exposed and unexposed regions was visualized. Our MD simulations reproduced differences in resist solubility depending on the type of developer that was observed in experiments. In the unexposed region, resist dissolution occurred as individual molecules, not as groups of molecules. As development progressed, swelling-induced expansion of intermolecular distances and the consequent decrease of intermolecular forces promoted dissolution in the unexposed region. In contrast, in the exposed region, developer penetration was restricted to near the surface and noticeable swelling was not observed.