Author ORCID Identifier

Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Electrical and Computer Engineering

First Advisor

Dr. Jeffrey Todd Hastings


Selective Electron Beam Etching of Materials Using Liquid Reactants Nanoscience and nanotechnology require advances in processing, patterning, and characterization of materials to overcome current limitations and generate new de-vices. Electron and ion beam-based processes are vital for fabrication and nano-scale prototyping with significant applications in nanoscale electronic, photonic, and magnetic devices; integrated circuit debugging; and lithographic mask and imprint template repair.

Focused ion and electron beams are routinely used to locally add (printing) or sub-tract (machining) materials. This type of material processing is becoming increasingly important to the integrated circuit manufacturing industry for editing and debug applications. Most significantly, as structures continue to scale down and increase in complexity, selective material removal has become considerably more challenging. Integrated circuits have a variety of materials densely packed across small geometry. Focused ion beam milling can remove materials but often damages underlying layers. Likewise, e-beam induced etching with gases relies on producing a volatile byproduct, and this prevents etching of many technologically essential materials such as copper and nickel. As a result, there is a need to develop new techniques to address many of these challenges.

Liquid, rather than gas, phase focused electron beam induced processes may over-come many of these challenges. Therefore, we have been investigating the theory and practice of etching metals using focused electron beams and liquid reactants as an alternative to the current gas-phase technique. The results can be applied directly to nanoelectronics integrated circuit edit, and to the repair of extreme ultra-violet (EUV) masks used in high perforce photolithography.

A comprehensive investigation of metal etching in liquids as a function of process variables has been provided. Studies and experiments of the variables that control the etching -such as electron beam current, liquid thickness, and does, have been made to determine the fundamental mechanisms of liquid phase focused electron beam induced etching. A predictive model for liquid phase focused electron beam induced etching of copper has been developed. This requires modeling of electron interactions with gas in the process chamber and the liquid. It also requires modeling of subsequent chemical reactions that lead to copper etching. Monte Carlo simulation was used for electron energy loss versus position in the liquid. The output was coupled with finite element simulations to model radiolysis processes, subsequent reactions, mass transport in liquid, and etch geometry. A good agreement was found between the simulated and experimental results.

For the liquid phase focused electron beam induced etching of copper experiments, We have designed an optical imaging system for the specimen chamber of a standard scanning electron microscopy that allows direct measurements of the liquid thickness and visualization of the liquid thin film topology. For Nickle etching, we have developed a straightforward quantitative assessment of the liquid film thickness by using nanocubes fabricated by means of two-photon lithography.

The understanding gained from these studies suggests a number of new research directions and should lay the foundation for new technological developments.

Digital Object Identifier (DOI)

Funding Information

The Higher Committee for Education Development in Iraq (HCED), the Ministry of Higher Education and scientific research in Iraq/Al-Furat Al-Awsat Technical University. (2014-2018)

The National Science Foundation under Grant No. CMMI-1538650. (2014-2020)

The National Science Foundation (ECCS-1542164). (2014-2020)

National Science Foundation Grant No. CMMI-1125998. (2014-2020)

Available for download on Wednesday, June 30, 2021