Patterning nickel for extreme ultraviolet lithography mask application I. Atomic layer etch processing

Abstract

The stringent requirement for patterning highly absorbing metal thin films as a mask for the next-generation extreme ultra-violet lithography system dictates the development of an atomic layer etching process to tailor the etch rate and the etch profile. A “plasma-thermal” atomic layer etching process is developed where an oxygen plasma is used to convert the metallic Ni layer into NiO, followed by formic acid vapor reacting with NiO to form nickel formate [Ni(COOH)2], thereby removing nickel. The directionality of the oxygen ions is used to create a directional chemical conversion of Ni into NiO, resulting in an anisotropic etch profile. Using the SiO2 patterned Ni thin film, a high etching selectivity to the mask (virtually no etching of SiO2) and a high etching anisotropy (a sidewall angle up to 87°) are achieved.