Quantitative Characterization Of Morphological Evolution In Q = 2 Potts Model Aluminum Thin Films
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QUANTITATIVE CHARACTERIZATION OF MORPHOLOGICAL EVOLUTION IN Q = 2 POTTS MODEL ALUMINUM THIN FILMS D. H. Alsem1 E.A. Stach2 and J. Th. M. de Hosson1 1. Department of Applied Physics, Materials Science, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands 2. National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA USA 94720 Abstract In this research, we have focused on the morphological evolution of a model metal film / silicon substrate system. When aluminum (Al) is physical vapor deposited on (100) oriented single crystal silicon (Si) at 280°C it grows heteroepitaxially. Crystallographically, the resulting films are a Potts model system with degeneracy two; their topology simulates a polycrystalline grain structure, with the two types of grains enveloping each other in a convoluted, maze-like arrangement. The morphological evolution of the films during annealing was determined via a combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM). Films with thickness’ of 100 to 500 nm were annealed in-situ in the TEM from 250°C to 550°C, and characterized using a (220) two-beam condition from one of the grain orientations. This yields predominantly white on black images, which are amenable to quantitative image processing techniques. As anticipated, the grain size increased linearly during the first annealing cycle. Also so-called sub-grain boundaries were observed. These low angle boundaries originate during film deposition when arrays of dislocations are introduced in the areas where coalescing islands of the same orientation meet. After cooling and reheating the sub-grain boundaries disappear. This happens because upon cooling, misfit dislocations were introduced into the films to relieve the thermal misfit strain, resulting in a dense array of dislocations at the film / substrate interface. These thermal misfit dislocations interact strongly with pre-existing sub-grain dislocations; this, in effect, heals the microstructure. Introduction A quantitative and predictive understanding of morphological evolution and mechanical behavior of metallic thin films is necessary for successful processing of electronic devices. When idealized film systems are observed, a general quantitative and predictive understanding can be obtained. Al is a typical non-magnetic facecentered cubic material. Additionally, polycrystalline (Al) thin films are widely used in electronic applications, in magnetic and optical devices and in different types of coatings. The goal of this research was to find how the morphology of mazed bicrystal Al films evolves, i.e. how the grain size and shape changes during heat treatment. The methods used were in-situ transmission electron microscopy (TEM) for grain size and shape determination and atomic force microscopy (AFM) for surface analysis. Automated image analysis tools were developed to extract the data from the TEM images.
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Q=2 Potts model Al films
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Figure 1: Tiling in a two dimensional
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