Nucleation and initial growth of diamond film on Si substrate
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B. W. Sun Institute of Physics, Chinese Academy of Sciences, Beijing, China Z. Zhanga> Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, P. O. Box 2724, 100080 Beijing, China Z. Lin Institute of Physics, Chinese Academy of Sciences, Beijing, China (Received 18 June 1993; accepted 3 June 1994)
A high resolution electron microscopic (HREM) study of interface structure between diamond film and its silicon substrate is presented. The HREM images reveal that there is an amorphous intermediate layer between the diamond film and its substrate for samples grown by hot filament chemical vapor deposition (HF-CVD). In some cases, /3-SiC crystallites and a few graphite microcrystallites may be embedded in this amorphous layer. The HREM images obtained from cross-sectional specimens reveal that the diamond crystallites nucleate directly either on the amorphous intermediate layer, at diamond seed crystallites that were left during pretreatment of Si substrate by diamond paste, y8-SiC particles, or at some scratches of the Si substrate. HREM images also reveal that the quantity, distribution, and the size of /3-SiC particles in the intermediate layer are different for different processes. Some /J-SiC crystallites have certain orientation relationships with the Si substrate. A HREM study of cross-sectional specimens indicates that twins and microtwins in the HF-CVD diamond film are formed during nucleation of the film either from diamond seeds, /3-SiC crystallites, or the amorphous intermediate layer. Multiple twins formed from different /8-SiC crystallites have also been observed. High densities of "V" shaped microtwins formed during the initial growth of the diamonds and the formation mechanism of these twins are discussed.
I. INTRODUCTION Nucleation and growth are different processes, but they are related to each other. The density and the rate of nucleation strongly influence the properties of the diamond films and have, therefore, been subjects of great interest recently. Ma et al.l reported that there is a polycrystalline Si intermediate layer between the diamond film and its Si substrate. This layer was formed, during deposition of the diamond film, by crystallization of an amorphous layer induced by the pretreatment of the Si substrate. Williams and Glass2 observed a /3-SiC intermediate layer about 5 nm in thickness between the diamond film and its Si substrate. Kobayashi et al.3 reported that the intermediate layer is amorphous. Turner et al.4 reported that the facet nuclei formed along the scratches on the substrate. Singh and Vellaikal5 found that large diamond crystallites were grown from small diamond
^Address all correspondence to this author. J. Mater. Res., Vol. 9, No. 10, Oct 1994
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microcrystallites which were formed as a result of direct transformation of diamond-like carbon into diamond. Iijima et al.6 reported that seed crystals provided sites for subsequent growth of diamond films. It is apparent that there are still many critical
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