1. A method of forming a silicon oxynitride antireflection coating over a metal layer, comprising: providing a semiconductor substrate comprising the metal layer over at least part of the semiconductor substrate; depositing a silicon oxynitride layer over the metal layer having a thickness from about 100 &angst; to about 1500 &angst;; and forming an oxide layer having a thickness from about 5 &angst; to about 50 &angst; over the silicon oxynitride layer to provide the silicon oxynitride antireflection coating.