Gas-assisted focused electron beam and ion beam processing and fabrication

Utke, Ivo; Hoffmann, Patrik; Melngailis, John

doi:doi:10.1116/1.2955728

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Journal of Vacuum Science & Technology B / Volume 26 / Issue 4 / Review Article

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J. Vac. Sci. Technol. B 26, 1197 (2008); http://dx.doi.org/10.1116/1.2955728 (80 pages)

Gas-assisted focused electron beam and ion beam processing and fabrication

Ivo Utke¹, Patrik Hoffmann², and John Melngailis³

¹EMPA, Swiss Federal Institute of Materials Testing and Research, Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland
²Advanced Photonics Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
³Department of Electrical and Computer Engineering, Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742

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(Published online 11 August 2008)

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Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

ACKNOWLEDGMENTS

The authors would like to thank V. Friedli and T. Bret for a critical reading of the article and K. Edinger, J. Mulders, V. Callegari and S. Babin for material and data they provided. I.U. acknowledges financial support from the EU project NanoHand. To direct inquiries from readers and for proper attribution: the fundamentals and models of the processes, the organization of all the data, and descriptions of many of the applications are due to I.U., the gas chemistries are due to P.H., and J.M. contributed to the overall content and conception of the article, particularly the FIB material. In spite of search engines and the large number of references, the authors may still have missed important work. The authors apologize if this is the case and ask to be informed.

Article Outline

INTRODUCTION
1. Electron and ion beams
2. Electron and ion beam properties
  1. Electron beams
  2. Focused ion beams
3. Characteristics of incident primary electron and ion beams
PRINCIPLES AND FUNDAMENTALS OF GAS-ASSISTED FEB AND FIB DEPOSITION AND ETCHING
1. Nonlocal surface effects due to electron and ion interactions
  1. Interaction mechanisms
  2. Energy spectra of emitted electrons and of activated surface atoms
  3. Radial density distribution of surface interactions
2. Electron interaction with molecules
  1. Electron interaction with gas phase molecules
  2. Electron interaction with adsorbed molecules
  3. Electron stimulated desorption
  4. Physical sputtering due to electrons
3. Ion interaction with molecules
  1. Ion interaction with adsorbed molecules
  2. Physical sputtering due to ions
4. Impinging precursor flux
  1. Molecule flux in chambers and at tube exit
  2. Spatial distribution of molecule flux
  3. Shadow effects
  4. Gas phase related processes
5. Precursor migration
  1. Adsorption and desorption
  2. Surface diffusion
  3. Electrostatic field mediated phenomena
6. FEB/FIB heating
  1. Plane bulk geometry
  2. Pillar geometry
  3. Membranes
FEB AND FIB CONTINUUM MODELS
1. Steady state solutions
2. Parameter determination from steady state exposures
3. Time dependent solutions for pulsed irradiation
4. Parameter determination from raster scan exposures
5. Conditions for the electron- or ion-limited regime
6. Models accounting for several species of adsorbates
MONTE CARLO MODELS FOR GAS ASSISTED FEB INDUCED DEPOSITION
1. Monte Carlo models without precursor dynamics
2. Monte Carlo models with precursor dynamics
PRECURSOR MOLECULES
1. General aspects
  1. The role of residual molecules in microscope chambers
  2. Precursor stability
  3. Vapor pressure and evaporation enthalpy
2. Complexes for deposition
  1. Organic compounds for C deposition
  2. Hydrides
  3. Halides
  4. Carbonyls
  5. Pure phosphines and halogenophosphines
  6. Organometallics
  7. Acetylacetonates
  8. Alkoxides, nitrates, and amides
  9. Precursors for oxide deposition (dielectrics)
  10. Postdeposition treatments
3. Precursors and additional reactive gases
  1. Metals, metal oxides, and metal nitrides
  2. Pure silicon dioxide (SiO₂)
4. Etchants
  1. FEB gas-assisted etching
  2. FIB gas enhanced etching
5. Nonvolatile compounds
PROCESS CONTROL AND CHARACTERIZATION OF DEPOSITS
1. Time-resolved process control
  1. Reflectometry
  2. Monitoring of sample current and secondary electron signal
  3. Mass sensing
  4. In situ electrical resistance measurements
  5. In situ observation studies
2. Composition and substructure
3. SEM integrated mechanical measurements
APPLICATION FIELDS IN RESEARCH AND INDUSTRY
1. Repair of photomasks
2. Scanning probe sensors
3. Circuit editing
4. Nanophotonics
5. Micro- and nanoelectronics
  1. Insulators and resistors
  2. Electrical contacts
  3. Laboratory prototype devices
6. Field emitters
7. Mask fabrication for pattern transfer
8. Mechanical applications
9. Biorelated applications
SUMMARY AND OUTLOOK
1. FEB versus FIB
2. Process regimes
3. Precursor molecules and deposit purity
4. Fragmentation channels and reaction paths
5. Resolution
6. Models
7. Fundamental issues
8. Future prospects
  1. Helium ion beam
  2. Projection maskless patterning

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KEYWORDS and PACS

Keywords

electron beam deposition, electron beam effects, electron beam machining, focused ion beam technology, ion beam assisted deposition, ion beam effects, ion implantation, masks, milling, nanopatterning, reviews, sputter etching, AuCIPF3, Me2Au(acae), Me2Au(tfa)

PACS

81.16.Rf

Micro- and nanoscale pattern formation
01.30.Rr

Surveys and tutorial papers; resource letters
81.15.-z

Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz

Deposition technology
81.15.Jj

Ion and electron beam-assisted deposition; ion plating
81.20.Wk

Machining, milling

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History

Received 16 January 2008
Accepted 3 June 2008
Published online 11 August 2008

Digital Object Identifier

http://dx.doi.org/10.1116/1.2955728

PUBLICATION DATA

ISSN

1071-1023 (print)

1520-8567 (online)

Publisher

American Vacuum Society

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