Non-thermal deposition of films and structures

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Ion-beam Assisted Thin Film Growth Using Hyperthermal Ions

Fig. 1: View of the streaming nitrogen plasma from a constricted glow-discharge plasma beam source.
Fig. 2: Exit ion optics of a quadrupole system designed for energy and mass selected ion-beam assisted deposition (EMS-IBAD).
Fig. 3: Stability regions of the quadrupole system for different ion species present in a hyperthermal nitrogen ion beam; the ion beam current was measured at the sample position.

Many physical vapor deposition techniques for deposition of thin and ultrathin films or nanostructures are characterized by the fact that an intrinsic or an intended external irradiation with low-energy particles takes place (Fig. 1). These particles contribute on the one hand directly to film growth by their incorporation into the growing film and on the other hand indirectly by distinctly influencing the microscopic growth processes at the surface of the growing film via energy and momentum transfer in atomic collisions. This eventually influences the resulting film properties. Energetic particles with kinetic energies ranging from several 1 eV to a few 100 eV - called the regime of hyperthermal energies - are of particular interest, as in this energy regime the generation of collisionally induced point defects in the near surface region of the irradiated film is still small and can be minimized by choosing low particle energies in the range of the displacement energy (several 10 eV). As these processes take place far from thermodynamic equilibrium, this can e.g. lead to a reduction of the required substrate temperature while the quality of the deposited film remains high.

 

Using ion-beam assisted deposition (IBAD) or ion-beam assisted molecular beam epitaxy (IBA-MBE), a hybrid of conventional thin film and ion-beam techniques, thin films with modified or optimized properties can be synthesized. This technique is distinctive in that during deposition in vacuum the thin film is simultaneously subjected to irradiation with an energetic ion beam. By this, an additional energy and momentum input into the surface of the growing film is present, which can influence surface diffusion processes in order to optimize crystallinity and microstructure of the resulting thin film. Advantages of this technique are the high controllability of the deposition process due to the well-separated material fluxes, the wide parameter range, as well as the possibility to deposit amorphous, polycrystalline and nearly single crystalline thin films (LINK). The main application area of this technique at the IOM is the synthesis of nitride thin films like e.g. GaN, TiN or GdN.

A higher degree of sophistication of this technique by increasing the number of degrees of freedom was reached at the IOM by the realization of energy and mass selected ion-beam assisted deposition (EMS-IBAD). In this variant of the technique, selectability of the specific nitrogen ion species used for film growth (atomic nitrogen ions N+ or molecular nitrogen ions N2+) is accomplished by placing a custom-designed, tailor-made system of quadrupoles between ion source and sample (Figs. 2 and 3). This unique setup, meant for basic research in the field of ion beam assisted deposition processes, helps to explore the influence of the respective ion species on film growth (or on film erosion at higher kinetic energies) in more detail as before and to harness the results for further optimization and controllability of thin film properties.

Deposition technique variants

  • Ion-beam assisted deposition (IBAD) of polycrystalline thin films
  • Ion-beam assisted molecular beam epitaxy (IBA-MBE)
  • Energy and mass selected ion-beam assisted deposition (EMS-IBAD)

 

Selected publications

  • B. Rauschenbach, A. Lotnyk, L. Neumann, D. Poppitz, J.W. Gerlach
    Ion beam assisted deposition of thin epitaxial GaN films
    Materials 10 (2017) 690-702
    https://doi.org/10.3390/ma10070690

  • J.W. Gerlach, P. Schumacher, M. Mensing, S. Rauschenbach, I. Cermak, B. Rauschenbach
    Ion mass and energy selective hyperthermal ion-beam assisted deposition setup
    Rev. Sci. Instrum. 88 (2017) 063306
    https://doi.org/10.1063/1.4985547

  • D. Poppitz, A. Lotnyk, J.W. Gerlach, J. Lenzner, M. Grundmann, B. Rauschenbach
    An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE
    Micron 28 (2015) 1-8
    doi.org/10.1016/j.micron.2015.03.006

  • A. Finzel, J.W. Gerlach, J. Lorbeer, F. Frost, B. Rauschenbach
    High-fluence hyperthermal ion irradiation of gallium nitride surfaces at elevated temperatures
    Appl. Surf. Sci. 317 (2014) 811-817
    doi.org/10.1016/j.apsusc.2014.09.006