Role of Si(100) Surface Patterns in the Phase Separation of Cu/Sn Thin Films
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Role of Si(100) Surface Patterns in the Phase Separation of Cu/Sn Thin Films Qin Hu, Martin Zinke–Allmang and Ian V. Mitchell Department of Physics and Astronomy, The University of Western Ontario London, Ontario, Canada N6A 3K7 ABSTRACT We report on the competitive phase separation of copper and tin thin film deposits on a pre–patterned Si(100) surface. The initial pattern on Si(100) was achieved through a thermal decomposition process of an ex–situ grown oxide film. Copper and tin phase separation on silicon is a competitive process with Cu forming preferrably silicide. Sn is observed to cover the silicide clusters when present in a sufficient amount. The pre–patterning of the surface introduces a new length scale in the problem. Our data suggest that this length scale plays a role while the clustering (ripening) length scale is of the same order, i.e., during nucleation and the early phase separation, but that both length scales become independent once the length scale of ripening significantly exceeds the length scale of the surface pattern. INTRODUCTION Phase separation phenomena on surfaces have been studied intensively during the past two decades with two objectives: (i) to obtain a fundamental understanding of the dynamics of the evolution of low–dimensional systems and scale dependent properties of matter and (ii) to enable technological advances previously unattainable for thin film and heterostructure growth. While simple model systems have been chosen to establish fundamental concepts such as Ostwald ripening, coalescence and self–similarity, the ultimate application to technologically relevant cases requires to consider more complex scenarios. In particular, lithographically pre–patterned surfaces represent a new challenge as the existing patterns on the substrate will interfere with the propensity toward clustering and the dynamics of phase separations in a thin, deposited film. The anticipated interference includes local effects such as structures acting as mass transport barriers or serving as heterogeneous nucleation sites. We also expect long–range effects affecting the propensity toward a self–similar morphological evolution since the surface pattern defines a second, independent length scale for the process. The current study is a first, survey–type presentation of a system where both, a complex clustering system and a pre-patterned surface were combined. We chose a Si(100) surface on which a high density of inverse pyramidal grooves with a wide range of diameters (up to about 0.5 P DUHSUHVHQW2QWKLVVXUIDFHZHGHSRVLWHG&XDQG6QOD\HUVLQDYDFXXPGHSRVLWLRQV\VWHP
Extensive previous measurements for either film material on Si(100) and Si(111) and a recent study of competing clustering of Cu and Sn on Si(111) [1] provide us with a wide range of phenomena we want to survey on the pre-patterned surface in this paper. SAMPLE PREPARATION Commercial, polished n–type Si(100) wafers were cut and chemically cleaned by a repeated
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etching and re–oxidation procedure. In the last re–oxid
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