In Situ Spectroscopic Ellipsometry Study of the Oxide Etching and Surface Damaging Processes on Silicon Under Hydrogen P
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DOE-HiCREST scholar, University of Puerto Rico, Dept. of Physics, PO Box 23343,
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San Juan, PR 00931 (USA) University of Puerto Rico, Dept. of Chemistry, PO Box 23334, San Juan, PR 00931 (USA) University of Puerto Rico, Dept. of Physical Sciences, PO Box 23323, San Juan, PR 00931 (USA), [email protected]
ABSTRACT We employed in situ ellipsometry in the monitoring of surface damage to monocrystalline silicon (Si) substrates under hydrogen plasma conditions. These measurements were complemented with spectroscopic ellipsometry and Raman spectroscopy, in order to characterize the surface conditions. It was found that heating the Si substrate to 700 TC in the presence of molecular hydrogen produces etching of the native oxide layer, which is typically 10 A thick. When the already hot and bare silicon surface is submitted to hydrogen plasma, it deteriorates very fast, becoming rough and full of voids. Modeling of the spectroscopic ellipsometry data was used to obtain a quantitative physical picture of the surface damage, in terms of roughness layer thickness and void fraction. The results indicate that by the time a thin film starts to grow on these silicon surfaces, like in the chemical vapor deposition of diamond, the roughness produced by the hydrogen plasma has already determined to a large extent the rough nature of the film to be grown.
INTRODUCTION Plasma-enhanced chemical vapor deposition is a film fabrication technique widely employed in Materials Science. In particular, polycrystalline diamond thin films are currently produced by a variety of plasma techniques that include hot-filament and microwave plasma enhanced chemical vapor deposition, among others.' These polycrystalline diamond films typically show rough surfaces that make it difficult to deposit metallic structures on them. The surface roughness of currently available diamond films is a limitation for some of its potential electronic applications. 2
295 Mat. Res. Soc. Symp. Proc. Vol. 591 © 2000 Materials Research Society
In order to help determine whether the origin of this problem is intrinsic to diamond growth habits, or if it is a consequence of the harsh conditions created by the hydrogen plasma in the chemical vapor reactor, we have characterized the silicon substrate surface as it goes through the substrate preparation steps prior to diamond film fabrication. In this paper, we present a combination of kinetic ellipsometry 3 characterization of the silicon surface under actual plasma conditions, and spectroscopic ellipsometry and Raman spectroscopy taken on the cold films. These data allowed to obtain a physical picture of the damage caused to the silicon surface by the hydrogen plasma, in terms of the thickness of the roughness layer and its void fraction. EXPERIMENTAL
Commercially available, polished, (100) silicon substrates were used in this study. They were only rinsed in methanol before placing them inside the reactor. We used the same set-up that we employ for diamond film deposition, which is described in detail elsewhere.
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