A method of processing a substrate is disclosed herein. The method includes applying a photoresist layer comprising a photoacid generator to a substrate, wherein a first portion of the photoresist layer has been exposed unprotected by a photomask to a radiation light in a lithographic exposure process. The method also includes applying an electric field to alter movement of photoacid generated from the photoacid generator substantially in a vertical direction, wherein the electric field is applied by a first alternating pair of a positive voltage electrode and a negative voltage electrode and a second alternating pair of a positive voltage electrode and a negative voltage electrode.