The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Rate Equation Modeling of Hyperthermal Surface Growth

Mika Olavi Jahma

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F at Helsinki University of Technology (Espoo, Finland) on the 14th of December, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9114-4)   [1198 KB]
Dissertation is also available in print (ISBN 978-951-22-9113-7)

Abstract

The miniaturization of electronics in the past decades has lead to a situation where the size of current state-of-the-art microelectronic devices is approaching the nanometer length scale. The current methods of microelectronics, which can be used to control the fabrication of the manufacturing on atomic level, can be used only in limited conditions, and new methods are needed. This is especially acute as the recent advances in nanotechnology have given new tools for further development in microelectronics. Molecular Beam Epitaxy (MBE) is currently perhaps the most important atomic scale method for fabricating epitaxial thin films. The quality of films is very high and control over the growth of them is possible on the atomic scale. However, the MBE method works only under quite restricted growth conditions. At low temperatures it often leads to rough surfaces and three dimensional structures instead of smooth epitaxial films. The same happens when the deposition flux is increased. The limiting factor is the rate of surface diffusion, which should be high compared to the deposition rate, in which case the deposited atoms have enough time to diffuse on the surface and form clusters.

In this Thesis submonolayer growth has been studied using Rate Equation formulation. Rate equations provide a flexible and computationally effective tool to model complex island growth phenomena and are particularly suitable in ion beam assisted deposition (IBAD) and low energy ion deposition (LEID) type of growth conditions. In IBAD and LEID the surface is under constant ion bombardment and growth is thus explicitly a nonequilibrium phenomenon. The advantage of such Hyperthermal Deposition (HTD) methods over the MBE is a higher deposition rate during the growth process. Also, control over the quality of the atomic layers is better.

The results presented in this Thesis suggest that there is possible improvement to be gained from experimental studies of submonolayer island growth. A more detailed knowledge of diffusion of islands on different surfaces and the detailed measurements of island break-up probabilities under various growth conditions could lead to more quantitative descriptions of growth in computationally inexpensive and flexible models, which could be used to find the optimal growth conditions and extend the limits of the current thin film manufacturing methods.

This thesis consists of an overview and of the following 6 publications:

  1. I. T. Koponen, M. O. Jahma, M. Rusanen, and T. Ala-Nissila, Submonolayer growth with anomalously high island density in hyperthermal deposition, Physical Review Letters 92, 086103 (2004), 4 pages. © 2004 American Physical Society. By permission.
  2. J. Frantz, M. O. Jahma, K. Nordlund, and I. T. Koponen, Low-energy deposition of Co onto Co islands on Ag(100): Effect on submonolayer growth, Physical Review B 71, 075411 (2005), 8 pages. © 2005 American Physical Society. By permission.
  3. M. O. Jahma, I. T. Koponen, and M. Rusanen, Island size distributions in submonolayer growth in hyperthermal deposition, Surface Science, Volumes 566-568, Part 1, Proceedings of the 22nd European Conference on Surface Science, 20 September 2004, pages 170-174.
  4. M. O. Jahma, M. Rusanen, A. Karim, I. T. Koponen, T. Ala-Nissila, and T. S. Rahman, Diffusion and submonolayer island growth during hyperthermal deposition on Cu(1 0 0) and Cu(1 1 1), Surface Science, Volume 598, Issues 1-3, 20 December 2005, pages 246-252.
  5. M. O. Jahma, I. T. Koponen, and T. Ala-Nissila, Optimal conditions for submonolayer nanoisland growth in ion beam assisted deposition, Surface Science, Volume 601, pages 5628-5634 (2007). In press (Surface Science). doi:10.1016/j.susc.2007.09.037.
  6. T. Huhtamäki, M. O. Jahma, and I. T. Koponen, A simple model for quantifying the degree of layer-by-layer growth in low energy ion deposition of thin films, Nuclear Instruments and Methods in Physics Research B, Volume 264, pages 55-60 (2007). doi:10.1016/j.nimb.2007.08.073.

Keywords: island growth, thin films, ion beam assisted deposition, low energy ion deposition, rate equations, hyperthermal deposition, particle coalescence method

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© 2007 Helsinki University of Technology

Last update 2011-05-26