Abstract: A method of forming a shallow trench isolation is provided. In the method, a barrier oxide layer is formed on a substrate, and a silicon nitride layer is formed on the barrier oxide layer. A metal layer is formed on the silicon nitride layer, and an ultra-thin photoresist is formed on the metal layer. The ultra-thin photoresist layer is patterned with short wavelength radiation to define a pattern for a shallow trench. The ultra-thin photoresist layer is used as a mask during a first etch step to transfer the shallow trench pattern to the metal layer. The first etch step includes an etch chemistry that is selective to the metal layer over the ultra-thin photoresist layer. The metal layer is used as a hard mask during a second etch step to form the shallow trench by etching portions of the silicon nitride layer, barrier oxide layer and substrate.