Improving resist resolution and sensitivity via electric-field enhanced postexposure baking

This article explores a methodology for enhancing the resist resolution and improving resist profile based on confining the photoacid drift/diffusion by an external electric field. A properly offset alternating electric field applied to the resist film during postexposure bake (PEB) can enhance the photoacid drift in the vertical direction, drive acid to the desired direction, and thereby confine the lateral acid diffusion. The experiments were conducted on UVIIHS resist with JEOL electron-beam exposure tool and UVII-10 resist on ASML KrF stepper, respectively. The scanning electron microscopy pictures show that electric-field enhanced PEB can control the resist profiles and increase the verticality of resist sidewalls. Electric-field-enhanced PEB also significantly improves the tolerance of over and underexposure and provides better critical dimension control. It is estimated that it reduces the lateral acid diffusion length by about 70–90 nm in KrF lithography.