Some embodiments relate a method of forming a photomask for a deep ultraviolet photolithography process (e.g., having an exposing radiation with a wavelength of 193 nm). The method provides a mask blank for a deep ultraviolet photolithography process. The mask blank has a transparent substrate, an amorphous isolation layer located over the transparent substrate, and a photoresist layer located over the amorphous isolation layer. The photoresist layer is patterned by selectively removing portions of the photoresist layer using a beam of electrons. The amorphous isolation layer is subsequently etched according to the patterned photoresist layer to form one or more mask openings. The amorphous isolation layer isolates electrons backscattered from the beam of electrons from the photoresist layer during patterning, thereby mitigating CD and overlay errors caused by backscattered electrons.