(651d) Atomic Layer Etching of Ni-Based Materials By Nitridation

Ni and Ni-based alloys are being explored by the semiconductor industry for their use in state-of-the art interconnect technologies and in extreme ultraviolet (EUV) lithography applications. Etching Ni controllably, anisotropically, and selectively at the nanometer scale can be difficult, however, and to date this has limited application of Ni-based materials. Atomic layer etching (ALE) has been used to pattern many metals, but most ALE processes reported to date rely on halogenation or oxidation, which can complicate integration due to corrosion or low etch selectivity.

In this work, an ALE process is presented relying on plasma nitridation, formic acid vapor, and an Ar⁺ ion beam. This oxygen- and halogen-free process works by first forming a metastable Ni_xN at the surface using a remote plasma reactor, then removing the Ni_xN layer with the reactive formic acid vapor. The Ar⁺ ion beam is used to remove carbonaceous residues left by the formic acid. These three steps constitute an ALE cycle that can then be repeated to etch Ni at a rate of 1.3 nm/cycle. The formation of the Ni_xN as a function of plasma power and pressure is investigated, revealing the role of reactive radicals and ions in the formation of this metastable layer. Selectivity of the ALE process to other materials in semiconductor applications, such as Ru and SiN, is also examined.