Abnormal Gain Growth Behavior in Nanostructured Al Thin Films on SiO 2 /Si Substrates
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1150-RR06-03
Abnormal Gain Growth Behavior in Nanostructured Al Thin Films on SiO2/Si Substrates Flavia P. Luce1, Paulo F. P. Fichtner2, Luiz F. Schelp3 and Fernando C. Zawislak1 1
Instituo de Física, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil. 2 Escola de Engenharia, Universidade Federal do Rio Grande do Sul 91501-970 Porto Alegre, RS, Brazil. 3 Departamento de Física, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
ABSTRACT We report on the formation of nanocrystalline Al thin films (180 nm thick) via magnetron sputtering technique using a step-wise deposition concept where columnar growth is inhibited, giving place to the development of a nanocrystalline mosaic grain arrangement with characteristic diameters of ≈30 nm and small size dispersion. The thermal evolution of the grain size distributions is investigated by transmission electron microscopy (TEM) in samples annealed in high vacuum for 3600 s. For the temperature range 300 ≤ T ≤ 462 °C the system presents a 3-D regular growth behavior up to sizes ≈70 nm. For T = 475 °C a rather sharp transition from normal to abnormal grain growth occurs. The grains extend to the film thickness and present mean lateral dimensions of ≈1000 nm. The observed phenomenon is discussed in terms of a synergetic grain boundary mobility effect caused by the characteristics of the initial nanogranular grain boundary morphology.
INTRODUCTION Thin film structural features such as grain size, size distribution, texture and morphology can significantly influence the desired performance in many applications. For example, metallic interconnections of microelectronic devices with large, defect free grains are typically more resistant against electromigration failures than small grain size counterparts [1]. In contrast, the formation of nanosized grains presenting a monomodal size distribution and rather small size dispersion can improve the wear resistance of hard coatings [2]. In view of such wide variety of configuration requirements, there have been significant efforts to understand and model the grain formation and growth micromechanisms. Usually the deposited Al films have a columnar grain structure. During annealing treatments in most cases the grain size follows a monomodal distribution. However it has been observed that in some situations the coarsening can take place via abnormal grain growth [3]. Texturization and the release of strain energy are considerate important causes of abnormal grain growth [4].
In the present contribution we report on the formation of nanocrystalline Al thin films via magnetron sputtering technique using a distinct deposition concept, where columnar growth is inhibited and gives place to the development of a mosaic-like nanocrystalline grain arrangement with small size dispersion. The thermal evolution of the grain size distribution is investigated by transmission electron microscopy (TEM). As opposed to the usual concepts, in this particular structure arrangement a rather sharp transition
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