Deposition of diamond onto aluminum by electron cyclotron resonance microwave plasma-assisted CVD
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Diamond crystallites and thin films have been deposited onto polycrystalline aluminum substrates utilizing an electron cyclotron resonance microwave plasma-assisted chemical vapor deposition (ECR-PACVD) method. For all depositions, the substrates were biased to +40 V dc with respect to ground and their temperature was maintained at 500 °C. Similar deposits were obtained from two different feedgas systems at a total pressure of 1.33 Pa (10 mTorr). The first system consisted of a carbon monoxide (CO) and hydrogen (H 2 ) mixture (CO : H 2 = 20:80), and the second was a methane (CH 4 ), oxygen (O 2 ), and hydrogen (H2) mixture (CH4 : O2 : H 2 = 21:10:69). The deposits were subsequently characterized by scanning electron microscopy, micro-Raman spectroscopy, and x-ray diffraction. The results of these analyses indicate that polycrystalline diamond was deposited onto aluminum substrates, as both individual crystallites and continuous films. I. INTRODUCTION Diamond thin film technology has rapidly developed over the last decade to become a viable, promising commercial market.1 The thrust behind the rapid technological development lies in the extreme properties diamond possesses, which include high hardness, chemical inertness, and high thermal conductivity. 23 Such properties lend the material to a wide range of applications including heat transfer coatings, wear-resistant coatings, and transparent, protective coatings for optical components employed over the visible and the infrared regions of the electromagnetic spectrum.2 To date, most techniques for diamond deposition involve activated chemical vapor deposition (CVD) processes such as hot filament CVD,4 microwave plasmaassisted CVD, 5 and oxy-acetylene torch CVD,6 in which the substrate temperatures are typically 5=700 °C. Such conditions tend to exclude temperature sensitive materials such as low melting point metals, optical materials (such as ZnSe and ZnS), and metallized silicon chips from the benefits of diamond coatings. Recent studies involving both new and modified versions of existing deposition techniques have begun to reveal that it is possible to deposit diamond at temperatures s£600 °C.7"13 Deposition temperatures as low as 135 °C have been realized in hot filament assistedand microwave plasma assisted-CVD techniques through the use of aggressive active cooling of the substrates. New and emerging techniques, namely ECR-PACVD and halogen assisted-CVD, have inherently low growth temperatures without the need for active substrate cooling. ECR-PACVD has been pursued only over the last 4 - 5 years as a means to deposit diamond at low temperatures,7'12'14"16 but nearly all of these efforts used total pressures of 13.3 Pa (100 mTorr) or greater.
Most of the previous low temperature work involved deposition onto silicon and/or resulted in low density nucleation of the diamond phase. To date, there has been only one published report on the application of low temperature diamond deposition techniques to the materials for which they are intended (i.e., those with m
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