Growth Behaviour of Engineered Porous Thin Films - Measurement and Modeling
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GROWTH BEHAVIOUR OF ENGINEERED POROUS THIN FILMS – MEASUREMENT AND MODELING
D. Vick*, T. Smy**, B.Dick*, S. Kennedy*, M. J. Brett* *Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada T6G 2G7, [email protected] **Department of Electronics, Carleton University, Ottawa, ON, Canada K1S 5B6 ABSTRACT
Recent experimental work has demonstrated that unique high porosity thin films may be obtained in physical deposition systems by combining glancing angle deposition with in situ substrate motion control [1-7]. The microstructure of these films consists of isolated columns engineered into shapes such as helices, posts, or chevrons. Due to the isolated nature of the columns, the films present a unique opportunity to study fundamental thin film growth behaviour and, in particular, the influence of the self shadowing mechanism in three dimensions. Apart from this academic motivation, there is the need to characterize the physical constraints imposed on the engineering of these films. In particular, this study will have implications for the realization of isolated, periodically arranged nanostructures envisioned for certain applications. Preliminary results from an ongoing study of growth dynamics, morphology, porosity, and scaling behaviour, and the dependence of these features on deposition parameters are presented below. INTRODUCTION
Using the technique of glancing angle deposition, or GLAD [8], the orientation of a film substrate may be controlled during deposition in order to exploit self shadowing mechanism under conditions of collimated physical vapour flux. By this technique considerable control over the film density and shape of the isolated columnar structure has been demonstrated [9]. Possible applications of these films include embedding matrixes for optically active media [10], enhanced surface areas for sensor devices [11], or micro-sieves for the separation of biological materials [12]. In order to optimize the functioning of devices incorporating such films, control over the film density and shape of the film structure on sub-micron scale lengths will be necessary. Among the unresolved issues that remain to be addressed are the influence of material on the microstructure, and the degree to which control over column mean diameter and statistical column uniformity is possible. In order to begin to address these issues, an ongoing study of the growth using SEM and AFM analysis is being undertaken. Simulation work performed in parallel provides an interpretative aid in this investigation.
P3.43.1
GROWTH STUDIES ON PLANAR TOPOGRAPHY
In order to study morphological evolution of growing GLAD films, several SiO2 and Ti films were deposited by electron beam evaporation onto clean Si (100) substrates. The experimental system, described in greater detail in reference [9], features two computer controlled stepper motors which facilitate dynamic rotation of the substrate about two principle axes. The columnar morphology of the resulting films may be conveniently described usi
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