Processing of multilayer microcrystalline and nanocrystalline diamond thin films using Ar-rich microwave plasmas
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This article lays the foundation for the development of microwave plasma chemical vapor deposition process conditions for synthesizing multilayered microcrystalline and nanocrystalline diamond (MCD and NCD) thin films. The effects of gas composition and the diamond seeding medium are correlated with the film morphology and diamond phase purity. Results of process optimization experiments using single-layer diamond deposition indicate that for high gas-phase Ar content ($90%) the film quality improves with reduced Ar content and with increasing thickness reaching a plateau above a thickness of ;2 lm. Multilayer diamond deposition experiments with two different seeding media (25 nm and 1 lm) clearly show that it is feasible to selectively synthesize alternating MCD (60% Ar) and NCD (95% Ar) layers with good control of film quality and morphology, thereby setting the stage for development of multilayered diamond thin films with tailored properties for thermal management applications.
I. INTRODUCTION
Solid-state heat transfer plays a vital role in a variety of high-technology applications including microelectronics, power electronics, and high-power lasers. Efficient transport of heat from an operating device prolongs its lifetime and reduces system operating costs. In particular, effective thermal management is a critical technology requirement for wide bandgap semiconductor (primarily SiC and GaN) power electronics and solid-state lighting. High current densities in power devices generate a significant amount of heat, which needs to be rapidly dissipated to prevent device degradation and failure. An additional consequence of efficient thermal management is that devices can be operated at higher ambient temperatures leading to systems that will be compact, lightweight, energy efficient, and cost effective. Therefore, there is a critical need to develop effective thermal management materials and technologies for a wide variety of applications. The very high thermal conductivity of diamond (.20 W/cm K for single-crystal diamond) has attracted significant attention in recent years for thermal management applications.1–5 In particular, microwave plasma chemical vapor deposition (MPCVD) of diamond has enabled large-area conformal coatings of this material on a variety of substrates. Diamond thin films can be broadly classified into microcrystalline and nanocrystalline forms. MPCVD using H2-rich plasmas results in microcrystalline diamond (MCD) films. Although thick MCD (.50 lm) a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.396 3072
J. Mater. Res., Vol. 26, No. 24, Dec 28, 2011
http://journals.cambridge.org
Downloaded: 13 Mar 2015
films exhibit high thermal conductivities (.15 W/cm K),6 the surfaces of these films are very rough. The high surface roughness can be detrimental to effective heat transfer across interfaces because it can lead to significant scattering. Also, the columnar structure of MCD films can lead to highly anisotropic thermal properties, which may not be desirable in ce
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