Molecular Dynamics Simulation of Copper Deposition by Ion Beam Assisted Deposition and Physical Vapour Deposition Technique

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Title: Molecular Dynamics Simulation of Copper Deposition by Ion Beam Assisted Deposition and Physical Vapour Deposition Technique
Author: Odiyo, Alex Nyakumba
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2019
Language: eng
Thesis level: master's thesis
Discipline: Fysiikka
Abstract: Physical Vapour Deposition (PVD) is a method of thin film deposition that involves transport of materials in the gas phase through physical means. The greatest advantage of using PVD is its ability to deposit hard coatings that are almost impossible to deposit by other liquid or chemical deposition methods. The applications of PVD include semiconductor-fabricated devices, cutting and drilling tools, optical coating for displays, and decorative coatings for jewellery. When PVD process is accompanied by a separate (noble) gas ion bombardment, it is termed as Ion Beam Assisted Deposition (IBAD). These two processes can be subjected to atomistic simulation as opposed to conventional experimental methods. The idea behind such a simulation is the level of control in terms of material purity, dimensionality and simulation parameters. In this simulation, the growth and overall morphology of epitaxial growth of copper film under both PVD and IBAD is considered. The film roughness and intrinsic stress are subjected to testing under various deposition energies in PVD. The same properties are also tested under variation of different bombardment energies, and bombarding rates or ion fluence in IBAD. The results show that the nature of the film growth is primarily dependent on the deposition energy. In PVD, low deposition energies are dominated by island growth while high deposition energies are mainly layer-by-layer growth dominated. In IBAD done at a constant low atom deposition energy, a similar trend is seen with increasing argon ion bombardment energy at 0.5 ions/nm2 fluence. Since the deposition energy of 1 eV is geared towards island growth, conversion rate of island like structures to relatively layer-by-layer structure depends on the ion bombardment energy (IBAD case). On comparison of IBAD and PVD outcomes, it has been established that the best layered PVD film occurs at a deposition energy of 30 eV. The overall film quality (in PVD) with respect to layer-by-layer growth is much better than that deposited using IBAD at similar bombardment energy at an ion fluence 0.5 ions/nm2. However, to attain a comparable or superior layer-by-layer growth as PVD, IBAD process has to be conducted at a much higher bombardment energy (50 eV) at fluence of 0.5 ions/nm2. The other alternative is to undertake IBAD process at bombardment energy of 30 eV, and at a much higher ion fluence. At a fluence of 0.8 ions/nm2 and equivalent ion bombardment energy (30 eV) produces a far much superior structure to PVD growth. The tradeoff between which ion fluence to use in IBAD is the deposition rate. Higher ion fluence translates to slow deposition but much improved layer-by-layer structure. The stress profile shows a decreasing stress profile as a function of thickness as predicted by Stoney's equation. At non-equilibrium deposition conditions, the film is generally stressed. However, under optimal conditions for layer-by-layer growth, IBAD grown films are generally less stressed in comparison to PVD.

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