Smoothening of (001) and (111) Cu films epitaxially grown on Si substrates
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Smoothening of (001) and (111) Cu films epitaxially grown on Si substrates Rosa Alejandra Lukaszew1, Ctirad Uher and Roy Clarke Physics Department, University of Michigan, Ann Arbor, Michigan. 1 Presently at the Department of Physics and Astronomy, University of Toledo, Toledo, Ohio. ABSTRACT We report an in-situ study of the MBE growth of Cu films on hydrogen-terminated Si (001) and (7x7) reconstructed Si(111) substrates. Using correlated RHEED and STM data, we find a dramatic smoothing of epitaxial Cu(001) surfaces by annealing the asgrown films in the 120-160oC temperature range and somewhat less so for the Cu (111) films. Our measurements reveal a lower activation energy (0.40 + 0.04 eV) for interterrace mass transport in Cu(001) than for Cu(111) (1.10 + 0.03 eV) the former possibly influenced by the presence of hydrogen. Scaling analysis of the subsequent Cu growth on the annealed smooth surfaces yields a coarsening exponent of 1/4 for the (001) oriented films while this exponent is 1/3 for the (111) films, providing for the first time experimental data for the same system in these two orientations. INTRODUCTION Buffer layers are often used to stabilize the growth of epitaxial films. In particular, Cu buffer layers grown on silicon substrates are used extensively for subsequent growth of epitaxial magnetic multilayers. Unfortunately the appearance of roughness as a result of noise, strain and step-edge barriers is an important challenge to the development of applications of epitaxial metal layers. In the case of heteroepitaxy, strain due to lattice mismatch and interfacial chemical reactions can also play an important role in roughening [1]. Interestingly, various reports indicate that copper can be grown at room-temperature as a single domain film on (001)Si-H or (111)Si-7x7 surfaces, while it is not possible to grow single domain films on (111)Si-H or reconstructed (001)Si surfaces [2,3]. Thus, we describe here our results of an in-situ study comparing the mass transport kinetics of single domain (001) Cu films epitaxially grown on hydrogen terminated Si(100) and (111) Cu films epitaxially grown on 7x7 reconstructed Si(111), as well as the scaling behavior of growth parameters such as roughness and coarsening of the surface features. In order to anneal epitaxial copper films to achieve smoother surfaces, the temperature should be high enough to provide enough energy to overcome step-edge barriers. However, as the Cu-Si interaction is relatively strong, a p-d hybridization in the Cu-Si intermixing region results in silicide formation, even at 100K [4]. The thickness of this silicide is strongly temperature dependent, thus limiting the annealing temperature range. In the following we will show that it is possible to obtain smooth single-domain copper films in both (001) and (111) orientations, grown on Si, via a mild annealing in a temperature range below predominant silicide formation.
P11.36.1
EXPERIMENTAL Our studies were performed in a VG 80M molecular beam epitaxy (MBE) chamber equipped with an in-situ
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