Abstract: A method of forming a borderless contact, comprising the following steps. A substrate having an exposed conductive structure is provided. An oxynitride etch stop layer is formed over the substrate and the exposed conductive structure. An oxide dielectric layer is formed over the oxynitride etch stop layer. The oxide dielectric layer is etched with an etch process having a high selectivity of oxide-to-oxynitride to form a contact hole therein exposing a portion of the oxynitride etch stop layer over at least a portion of the exposed conductive structure. The etch process not appreciably etching the oxynitride etch stop layer and including: a fluorine containing gas; an inert gas; and a weak oxidant. The exposed portion of the oxynitride etch stop layer over at least a portion of the conductive structure is removed. A borderless contact is formed within the contact hole. The borderless contact being in electrical connection with at least a portion of the conductive structure.