Selective growth of polycrystalline diamond thin films on a variety of substrates using selective damaging by ultrasonic
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Polycrystalline diamond thin films have been selectively grown on silicon, silicon dioxide, silicon nitride, tantalum, molybdenum, alumina, and sapphire substrates using selective damaging by ultrasonic agitation. Processes were developed to selectively damage the substrates by ultrasonic agitation in methanol containing diamond particles of typical size 90 fim. Optical and scanning electron microscopy is used to study selectivity and morphology of as-grown diamond thin films.
I. INTRODUCTION Growth of polycrystalline diamond thin films using microwave plasma-assisted chemical vapor deposition has received significant interest in recent years, since it has unique chemical and physical properties.1 Many microelectronic applications require patterned polycrystalline diamond thin films. Patterning can be achieved by chemical etching, plasma etching, and/or selective growth. Polycrystalline diamond is highly resistant to chemical solutions. Therefore, diamond is very difficult to pattern by chemical etching, and it is also difficult to find a suitable mask material to withstand the solutions even if it can be chemically etched. Plasma etching is an alternate technique, but reactive ion etching of natural type IIA diamond with oxygen has resulted in poor etch selectivity between mask materials and diamond,2 although this technique has been further explored to increase the selectivity by xenon ion beam and nitrogen dioxide3; moreover, it also requires very complex equipment. A viable alternate technique is to pattern the polycrystalline diamond by growing selectively, and this can generally be achieved if the two regions on the substrate have nucleation density differing by several orders of magnitude. It is well known that nucleation density is very low on mirror-smooth finished IC (Integrated Circuit) device grade silicon substrates.4"10 This has been considered as a guideline to grow diamond selectively. Photoresist could not be used as a mask material during the growth since diamond is typically grown at a substrate temperature of 800-1000 T i n a microwave plasma process. A few attempts were made recently to grow diamond selectively on silicon substrate.11"21 Selective diamond growth is obtained by patterning the completely damaged mirror smooth finished surface. Hirabayashi and Taniguchi11 have achieved selectivity of diamond growth by damaging or roughening the complete surface of a silicon wafer in ethyl alcohol containing 15-30 1144 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 5, May 1992 Downloaded: 25 Mar 2015
diamond particles in an ultrasonic agitator. The resist pattern was then transferred to the roughened substrate by standard photolithography and finally, the surface not covered with resist resin was etched 500-600 A in depth by an Ar+ ion beam. A similar attempt was made by Kobashi et al,n achieving selective diamond growth by using diamond paste to damage silicon substrates, photolithographically patterning, and plasma etching the silicon in the undesired diamond growth areas to remove
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