Temporal evolution of surface structure and morphology in thin-film growth and etching processes.

摘要

The temporal evolution of surface structure and morphology in growth and etching processes is of great importance to the understanding of such processes. For example, by looking at the time dependence of the surface roughness, one can often discover the scaling symmetries inherent in a process. In addition to providing clues about what mechanisms might be at work, these symmetries are also of practical interest. While much effort has been devoted to understanding the basic mechanisms that influence the temporal scaling of such systems, many systems still cannot be explained in terms of the known universality classes.; Studies of both continuum and discrete models of surface roughening are presented. The temporal scaling of the Kuramoto-Sivashinsky (KS) equation has been studied using direct numerical integration, and the existence of two distinct scaling regimes is observed. The results are discussed in the context of previous computational and analytical results and compared to existing experimental studies of ion sputtering. It is found that low-energy ion sputtering experiments are consistent with the early-time KS scaling regime; while high-energy ion sputtering experiments are consistent with asymptotic Kardar-Parisi-Zhang (KPZ) behavior. Next, the temporal scaling behavior of a line-of-sight model of surface roughening has been studied. The model can be applied to both growth and etching processes. Several different limiting cases for the sticking coefficients have been examined using analytical arguments and computational techniques, and it is found that the scaling exponents are, in some cases, universal. The predicted scaling exponents, in some cases, do not belong to any of the known universality classes and therefore define a new universality class. In another case, the exponents are identical to the exponents predicted by the Edwards-Wilkinson equation. The newly discovered universality classes are used to explain experimentally observed behavior of plasma etching and chemical vapor deposition processes, which could not be explained by any of the previously known universality classes. More generally, these universality classes can help uncover what processes are most important in certain experimental systems.; The temporal evolution of copper films thermally evaporated onto silicon oxide has also been studied. The structure of the film was monitored, during deposition, using reflection high-energy electron diffraction (RHEED). The films are found to be polycrystalline with face-centered cubic (fcc) grains. The crystal structure and surface morphology are studied as functions of time, and it is found that competitive texture evolution occurs, leading to an absence of (111), (200), and (220) oriented grains. The growth of facets is also studied, and it is found that the facet size grows exponentially with time. This behavior is explained in terms of facet coalescence. The results presented here illustrate several new methods of analyzing RHEED patterns and demonstrate the usefulness of RHEED for real-time characterization of polycrystalline films.