Methods and apparatuses for minimizing line edge/width roughness in lines formed by photolithography are provided. In one example, a method of processing a substrate, the method includes applying a photoresist layer comprising a photoacid generator to a substrate, exposing a first portion of the photoresist layer unprotected by a photomask to a radiation light in a lithographic exposure process, and applying an electric field or a magnetic field to alter movement of photoacid generated from the photoacid generator substantially in a vertical direction.