AVS2004 Session TF+NS-TuA: Focused Beam Processing & Fabrication

Tuesday, November 16, 2004 2:20 PM in Room 303C

Tuesday Afternoon

Start	Invited?	Item
2:20 PM		TF+NS-TuA-4 Localized Heating Effects During Electron Beam-Induced Deposition of Nanostructures S. Randolph, J.D. Fowlkes, P.D. Rack (University of Tennessee, Knoxville) In recent years, electron beam-induced deposition (EBID) has shown promise for use in next-generation lithography applications and nanostructure fabrication. While many materials have been successfully deposited on various substrates by EBID, control of feature size and geometry has been lacking. One possible mechanism that makes process control problematic is the localized heating that occurs in the nanostructure while undergoing constant electron bombardment. While the electron beam-induced heating of a bulk sample in the typical SEM is negligible, a focused beam projected onto a raised high aspect ratio feature can cause significant temperature rises in the feature. As the sticking coefficient and residence time of the impinging precursor gas are strong functions of the substrate temperature, it is expected that the deposition rate will vary with the surface temperature of the nanostructure if the process is mass transport limited. Assuming that there are no radiative and convective heat losses through the surface of the sample, the nanostructure growth creates a quasi one dimensional structure that does not dissipate heat as well as a bulk film. Consequently, as the nanostructure grows the surface temperature increases thereby reducing the sticking coefficient and residence time of the impinging gas. In this presentation, a Monte-Carlo electron-solid model will be illustrated which calculates the energy deposition profiles in the bulk and nanostructured features. Using these profiles, a finite element model is used to calculate the temperature profiles. Bulk and nanostructured features will be compared and discussed in context with experimentally observed growth rates.
2:40 PM	Invited	TF+NS-TuA-5 Electron Beam Micromachining P.E. Russell, D.P. Griffis, A. Garetto (NC State University) While chemically enhanced focused ion beam micromachining (CE-FIBM) or other ion based micromachining techniques have many practical applications, any ion beam based micromachining technique typically results in some degree of sample damage as well as residual implanted ions. In many cases, these implanted ions cause deleterious effects such as staining in the case of mask repair, alteration of the electrical characteristics of semiconductor and optoelectronic samples and/or surface damage in samples prepared for high resolution electron microscopy or microanalysis. In order to avoid ion staining and following up on our earlier efforts in electron beam induced deposition and material removal, our efforts are currently focused on gaining increased understanding of and development of chemically enhanced electron beam micromachining (CE-EBM) of technologically important materials. The interaction of incident and emitted (secondary and backscattered) electrons with surfaces in the presence of a suitable chemical precursor can induce useful chemical reactions. Electron beam energies from a few hundred eV to 30 keV are routinely available on scanning electron microscopes, and a few systems allow much lower beam energy. The magnitude of the emission of secondary electrons peaks in the range of a few eV to tens of eV's while backscattered electrons are emitted over a broad, albeit higher range of energies up to the full primary energy. This wide range of electron energies coupled with the richness of possible beam/sample/precursor interactions makes available a wide range of possibilities for both deposition and etching with, when compared to damage resulting from ion beam exposure, a dramatically reduced probability of damage and/or unintentional alteration of samples. This talk will review recent developments in both the application and understanding of CE-EBM.
3:20 PM		TF+NS-TuA-7 Nanoscale Structures and Devices Produced Using Energetic Atomic Beams E.A. Akhadov (Los Alamos National Laboratory); D. Read (Florida State University); A.S. Cavanagh, A.H. Mueller (Los Alamos National Laboratory); J.C. Gregory, G.P. Nordin (University of Alabama in Huntsville); M.A. Hoffbauer (Los Alamos National Laboratory) Nanoscale patterning of polymeric materials and low temperature thin film growth become possible using atomic species with kinetic energies similar to chemical bond strengths. We have developed a technique exclusive to LANL, called Energetic Neutral Beam Lithography/Epitaxy (ENABLE), that utilizes energetic neutral atoms for materials processing at the nanoscale. In this presentation, we demonstrate the use of atomic oxygen for nanoscale polymer etching and atomic nitrogen for templated nitride thin film growth. High-precision nanoscale formations (<50nm) with aspect ratios exceeding 35:1 were fabricated in polymer films. Taking advantage of the low temperature thin film growth afforded by ENABLE, we have fabricated AlN-based structures using pre-etched polymeric templates for potential electronic, photonic, and nanofluidic applications.
3:40 PM		TF+NS-TuA-8 A Three - Dimensional Computer Simulation of Electron - Beam Induced Deposition (EBID) J.D. Fowlkes, P.D. Rack, S. Randolph (University of Tennessee, Knoxville) A simulation will be presented of the electron - beam induced deposition (EBID) process that was coded using the Matlab(R) program. The simulation has a Monte Carlo component to predict electron trajectories as well as elastic and inelastic electron â?" substrate interactons. A discretization scheme projects each electron scattering event onto a three dimensional matrix to provide a reference point to test for a host of possible events per matrix node including secondary electron generation and/or EBID. Three phases coexist in the matrix including the precursor gas, the deposited phase and the substrate phase. A dynamic model tracks the gas - surface interaction including precursor adsorption, deposition and desorption under thecontext of a Langmuir type surface coverage. Primary, backscattered, and secondary electrons that escape the gas - pillar and gas - substrate interface may induce deposition based on their trajectory, energy and precursor surface coverage. The probability of EBID is based on a "shifted and scaled" ionization cross-section for the precursor gas molecule to be roughly applied as a dissociation cross - section. Primary (PE) and secondary electrons (SE) contribute most signficantly to the EBID growth of high-aspect ratio nanopillars while backscattered electrons (BSE) play more of a feature coarsening role. Two regimes of pillar growth are observed; a region characterized by linear a growth rate where the electron interaction volume interacts with both the growing pillar and the substrate and a second regime, again linear in growth rate, whereby the penetrating electrons interact solely with the high aspect pillar.