Principles of atomic layer etching of metallic thin films

Abstract

Modern nanoscale fabrication requires precise control over both nanoscaledimensions and material properties. Atomic layer processes, such as atomic layerdeposition (ALD) and atomic layer etching (ALE), provide a conformal, smoothsurfaces with precise control on the dimensions. Both techniques rely on cyclic stepwiseprocessing where each step has self-limiting or quasi self-limiting behavior. ALD hasbeen well-established and developed over 40 years to grow various materials in acontrolled manner. ALE on the other hand, is still under development to overcome anumber of limitations. One of the major challenges for atomic layer processes is todetermine the optimal conditions to deposit or etch desired materials, which can only beachieved by understanding the molecular mechanisms of the processes. The workoutlined in this dissertation is dedicated to the mechanistic insights of atomic layerprocesses and utilizes several characterization techniques to have better understandingof the chemical reactions responsible for ALD or ALE. The main part of this work isfocused on uncovering the mechanisms of atomic layer etching of metallic thin films.Choosing the proper ALE method, especially for the materials that are hard to etch suchas cobalt and iron, is the first important step to design a successful ALE scheme.Moreover, maintaining the surface chemical composition and morphology is requiredfor realistic applications. Surface composition and chemical states of the key elementswere studied using various spectroscopic methods. Surface morphology and roughnesswere followed by microscopic techniques. Computational investigations were carried out to validate the proposed etching or deposition processes and to confirm importantspectroscopic observables.