Abstract
A multi-species Monte Carlo (MC) model, combined with an analytical surface model, has been developed in order to investigate the general plasma processes occurring during the sputter deposition of complex oxide films in a dual-magnetron sputter deposition system. The important plasma species, such as electrons, Ar+ ions, fast Ar atoms and sputtered metal atoms (i.e. Mg and Al atoms) are described with the so-called multi-species MC model, whereas the deposition of MgxAlyOz films is treated by an analytical surface model. Target–substrate distances for both magnetrons in the dual-magnetron setup are varied for the purpose of growing stoichiometric complex oxide thin films. The metal atoms are sputtered from pure metallic targets, whereas the oxygen flux is only directed toward the substrate and is high enough to obtain fully oxidized thin films but low enough to avoid target poisoning. The calculations correspond to typical experimental conditions applied to grow these complex oxide films. In this paper, some calculation results are shown, such as the densities of various plasma species, their fluxes toward the targets and substrate, the deposition rates, as well as the film stoichiometry. Moreover, some results of the combined model are compared with experimental observations. Note that this is the first complete model, which can be applied for large and complicated magnetron reactor geometries, such as dual-magnetron configurations. With this model, we are able to describe all important plasma species as well as the deposition process. It can also be used to predict film stoichiometries of complex oxide films on the substrate.
Highlights
A multi-species Monte Carlo (MC) model, combined with an analytical surface model, has been developed in order to investigate the general plasma processes occurring during the sputter deposition of complex oxide films in a dual-magnetron sputter deposition system
A hybrid model [24], which combines different individual models, can be implemented to make use of the advantages and to avoid the limitations of the different models and to achieve more reasonable computation times. Such a hybrid model is usually based on the fluid approach, and it exhibits the same disadvantages as mentioned above for magnetron discharges. Based on all these considerations, in this work we develop a so-called multi-species MC model [22], together with an analytical surface model [25] to describe the behavior of the important plasma species, as well as the deposition process of complex oxide thin films in a dual-magnetron discharge
Note that the fluxes of the sputtered Mg and Al atoms arriving at the substrate are calculated in the multi-species MC model
Summary
The collisions of the species considered in the model (i.e. electrons, Ar+ ions, fast Arf atoms and sputtered metal atoms), include elastic scattering, excitation to metastable and radiative states, ionization, charge transfer, etc and are presented in [22]. The calculation starts with the fast electrons (see detailed description in [8]), which are emitted at both cathodes upon impact of the energetic plasma species (i.e. mainly Ar+ and fast Arf) In this model, the initial number of the electron SPs emitted at the cathodes is 40 000. The SPs’ trajectory under the influence of both the electric and magnetic fields is calculated using Newton’s equations of motion, based on the Lorentz force This is true for the electron and Ar+ ion SPs. The Arf and metal atom SPs do not feel the influence of the electric and magnetic fields. The SC is assumed to be zero for fast Arf atoms and Ar+ ions, since Ar is an inert gas (note that Ar+ ions are reflected as neutrals) [16], whereas the SC of both Mg and Al (and for O2 at the substrate, at least in the case of a pure metallic film) is proposed to be unity, i.e. they are stuck when bombarding the surface [37]
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