Simultaneous Effects on Topography, Composition and Texture in Ion Assisted Deposition of Thin Films
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Simultaneous Effects on Topography, Composition and Texture in Ion Assisted Deposition of Thin Films James M.E. Harper Department of Physics, University of New Hampshire Durham, NH 03824 ABSTRACT Ion bombardment during deposition may simultaneously affect thin film topography, composition and crystallographic texture. Ion etching can produce periodic ripples that depend on the angle of ion incidence and surface temperature. When applied during deposition, ion bombardment can produce in-plane crystallographic orientation in polycrystalline materials for specific angles of incidence. In addition, ion bombardment changes the composition of multicomponent thin films according to the local angles of ion incidence and ion/atom ratios. Therefore, these three mechanisms may be linked under certain deposition conditions to generate novel topographically patterned materials with locally controlled composition and texture. Examples include metal alloys, oxides and nitrides, and recommendations for specific nanoscale structures are given. INTRODUCTION Ion bombardment (or other energetic particle bombardment) is commonly used during thin film deposition because it modifies materials in ways that may be essential to obtaining the desired properties. In plasma-based deposition systems, including magnetron sputtering, the degree of bombardment is typically not directly controlled. Ion beam assisted deposition systems, on the other hand, allow independent control of ion flux, energy and angle of incidence, providing means to identify the main components of bombardment that are responsible for property modification [1-4]. Three important effects of ion bombardment are modifications of topography, composition and texture (here, “texture” refers to crystallographic texture, or preferred orientation). In this paper, we explore the possibility of controlling simultaneously thin film topography, composition and texture. Using results from studies of ion etching and ion beam assisted deposition, we focus on the processes of periodic ripple formation, preferential sputtering and biaxial texture formation. By considering the angular dependence of these processes, we suggest that there are special conditions under which simultaneous control is possible. We propose a range of experimental conditions under which this control may be observed for several common types of crystal structure. Simultaneous control of properties allows the formation of self-patterned nanoscale heterogeneous structures and the growth of such structures on pre-patterned surfaces. The length scale of heterogeneity is in the range appropriate for nanotechnology applications. The ion beam direction also imposes anisotropy on the surface, giving directional material properties. Applications include directionally-sensitive detectors, anisotropic mechanical devices and electrically or optically anisotropic surfaces. While the methods described here are typically not used for single crystal materials synthesis, many properties of polycrystalline materials are improved b
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