The influence of the internal microstructure on the surface parameters of polycrystalline thin films
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The influence of the internal microstructure on the surface parameters of polycrystalline thin films C. Eisenmenger-Sittner and A. Bergauer Institut für Angewandte und Technische Physik, Technische Universität Wien, Wiedner Hauptstraße 8-10 A-1040 Vienna, Austria
ABSTRACT Physical Vapor Deposition (PVD) processes commonly lead to the formation of polycrystalline thin films due to the effects of island nucleation and growth. Scanning probe Methods such as Atomic Force Microscopy (AFM) or Scanning Tunneling Microscopy (STM) are widely used for the characterization of the film surface. The topographic data obtained from these measurements can be converted to roughness values, Power Spectral Densities (PSD's) or correlation functions. It is the objective of this paper to evaluate the possibilities to characterize the polycrystalline template which generates the film surface solely by quantities derived from topographic data. For this purpose roughness values, PSD's and correlation functions of polycrystalline Al-Films deposited on glass substrates and from simulated surfaces are compared. The main factors which influence the shape of PSD's and correlation functions are determined and possible connections between the constitution of the polycrystalline template (e. g. shape and size-distribution of the crystalline domains) and the film roughness are discussed.
INTRODUCTION
Whenever an initially smooth surface is exposed to a beam of incoming particles the growing interface begins to build up random, uncorrelated height fluctuations. Provided the flux of incoming particles is uncorrelated in space and time and no particle movement is allowed on the surface the spatial and temporal behavior of the surface fluctuations can be described by the mechanisms of kinetic roughening and dynamic scaling[1,2]. In case of a realistic growth process the roughness evolution is influenced by additional mechanisms of particle transfer along the growing surface which lead to the formation of laterally correlated features. The most prominent of these processes are island formation in the pre-coalescence phase, surface diffusion and surface energy minimization by the growth of grains bounded by low index crystallographic planes[3-6]. The activation of these surface relaxation events can depend on the deposition parameters (deposition temperature, deposition rate) and/or on film thickness. Each of the previously described processes has a characteristic influence on specific topographical properties of the film surface which can be assessed by Scanning probe techniques such as contact or non-contact Atomic Force Microscopy (AFM). It is the intention of this paper to compare several theoretical models for the different stages of film growth with experimentally assessed Power Spectral Densities (PSD’s) and Correlation Functions (CF’s) [7] obtained from O3.13.1
the surfaces of polycrystalline Aluminum-films deposited on amorphous glass substrates. The comparison with the experimental data shall give a general view how the surface geometry in
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