Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films
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1150-RR01-01
Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films James M.E. Harper Department of Physics, University of New Hampshire Durham, NH 03824
ABSTRACT Several methods to induce grain alignment in polycrystalline thin films are discussed, in which directional effects can dominate over the normal evolution of fiber texture during thin film growth. Early experiments with ion beam assisted deposition showed the importance of channeling directions in selecting grain orientations with low sputtering yield or low ion damage energy density. Examples of this approach include the formation of biaxial fiber textures in Nb, Al and AlN. Grain orientations may also be selected by the release of stored energy during abnormal grain growth initiated by solute precipitation (Cu-Co) or phase transformation (TiSi2). Other energy sources such as mechanical deformation, crystallization or compound formation may also contribute to producing desired grain alignments. In multicomponent thin films, combinations of these mechanisms provide opportunities for more specific control of grain orientations.
INTRODUCTION Thin film deposition often involves bombardment of the growing film by energetic particles including the depositing atoms themselves, process gas atoms (e.g. Ar) reflected from a sputtering target, ions attracted to the substrate by a bias voltage, and ion beams directed at the growing film. The latter is usually called Ion Beam Assisted Deposition (IBAD), and gives a high level of control over the deposition environment. At the request of the organizers of the Fall 2008 MRS Symposium RR on Artificially Induced Grain Alignment in Thin Films, this paper begins by summarizing the early development of IBAD at IBM Research. Next, the effects of releasing stored energy during abnormal grain growth are discussed as an approach for selecting grain orientation. Two examples are described in which this mechanism is initiated by solute precipitation and by phase transformation.
BACKGROUND In the mid-1970’s, radio frequency diode sputtering was developing as the preferred method for depositing thin films for silicon technology and memory devices. At IBM’s Thomas J. Watson Research Center, Jerome J. Cuomo was studying the effects of bias sputtering on thin film properties and recognized that an ion beam could provide a more controlled bombardment environment (ion energy, flux, angle) than the plasma in a diode sputtering system. In 1976, Cuomo and the author visited several ion source manufacturers, but none provided a configuration that could be conveniently operated within an electron beam evaporator or diode sputtering system. In 1977, Cuomo initiated collaboration with Professor Harold R. Kaufman,
inventor of the broad-beam, multiaperture ion source for space applications. Kaufman designed a dished set of ion source grids which enabled the beam from a 10-cm. diameter Ion Tech source to be focused onto small sputtering targets to obtain useful deposition rates. Using that source together with a 2.5-cm.
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