AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoA

Invited Paper TF-MoA4
Origin and Evolution of Sculptured Thin Films

Monday, October 25, 1999, 3:00 pm, Room 615

Session: Fundamentals and Applications of Ionized PVD
Presenter: R. Messier, Penn State University
Authors: R. Messier, Penn State University
V.C. Venugopal, Penn State University
P.D. Sunal, Penn State University
H. Maeda, Penn State University
Correspondent: Click to Email
Sculptured thin films (STFs) are columnar thin films prepared by directed vapor deposition under low adatom mobility conditions. Since the columns grow in the direction of the incoming vapor, and this column direction can be changed instantaneously, a new class of thin films can be engineered in which the STF nanostructural shapes can be sculptured into useful morphologies such as helices, matchsticks, chevrons, and periodically bent nematics. Wide variations in the exact STF shapes, as well as combinations of these morphologies, are possible through simple rotations of the substrate around two canonical axes. Potential applications include optical retardation layers for use in optical storage and communications systems, optical sensors for fluids of biological, chemical or nuclear significance, templates for biomaterials growth, and low-pemittivity materials for microelectronics. For normal angle deposition the columns generally expand and compete for growth evolution, thereby resulting in a cauliflower-like morphology. This is due to an in-plane, isotropic, atomic self-shadowing mechanism. Fortuitously, for large oblique angle deposition conditions ( „ 40š vapor incidence angle with respect to the substrate normal), typical for STF preparation, the columns become slanted, separated, and cylindrical due to an anisotropy in the self-shadowing process. Thus, the columns have a constant cross-section with film evolution - a requirement for many practical applications. It has been found experimentally, however, that under conditions of rapid or abrupt rotation of the substrate during oblique angle deposition, the columns expand, a situation which could limit their utility. In order to control STF morphology in the broadest sense, it is necessary to understand the details of the atomic clustering and growth competition process. In this paper a fundamental and yet practical approach will be presented for classifying the atomic self-shadowing processes in STF growth based upon previous experience in morphology evolution modeling and experiments. Recent experiments in STF growth include systematic changes in column growth rate / substrate rotation rate, use of textured substrates, and variations of low energy ion bombardment.