Electron Beam Driven Plasmas and the Quest for Precise Control in Materials Processing
Abstract: The advantages of plasma-based materials processing techniques are numerous. The capability to rapidly and uniformly modify large areas (> 103 cm2) with high precision is one reason plasmas are widely used in the materials and surface engineering communities. However, with the ever-volving demand for new materials and single nanometer-scale device dimensions across a variety of applications, some of the limitations of conventional plasma sources are becoming apparent. The lack of process control and excessive ion energies in the development of atomic layer processing strategies are examples.
The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma. Unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (~ keV) electron beam, an approach that can overcome many of the problems associated with conventional plasma processing systems. Electron beam-generated plasmas are generally characterized by high charged particle densities (1010- 1012 cm-3), low electron temperatures (0.3 - 1.0 eV), and in reactive gas backgrounds, a relatively low radical production rate compared to discharges. These characteristics allow the ability to precisely control the flux of charged and reactive neutrals as well as ion energy at adjacent surfaces. This provides the potential for controllably etching, depositing, and/or engineering the surface chemistry with monolayer precision.
An overview of NRL’s research efforts in developing this technology will be presented, with a focus on source development and operation, plasma characterizations, and how the system can be advantageously applied to the processing of select materials. Examples include graphene, where erosion and damage is a major concern and the etching of semiconductor materials, such as Si, SiN and SiO2, where the focus is on etch rates and selectivity at low ion energy. This work is supported by the Naval Research Laboratory base program.
Bio: Scott Walton is Head of the Plasma Applications Section in the Plasma Physics Division at the Naval Research Laboratory (NRL) in Washington DC. He manages the Plasma Applications Laboratory and research programs related to the production, characterization, and use of low temperature plasmas in applications for both low and high pressure environments. The programs cover topics ranging from fundamental studies of the plasma and plasma-surface interface to applications in materials processing and synthesis that are of interest to the Navy and DoD. These programs have provided the opportunity to collaborate with researchers from academia, national laboratories and industry to address challenging but exciting problems. He has published more than 100 peer-reviewed journal articles and was awarded 13 patents.
Dr. Walton received a B.S. in Physics from Bloomsburg University of Pennsylvania and a PhD in Physics from the College of William and Mary. He came to NRL as a National Research Council Postdoctoral Research Associate and has been a staff member in the Plasma Physics Division since 2002. He is a fellow of the AVS.
