Growth-rate dependence of the thermal conductivity of chemical-vapor-deposited diamond
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Growth-rate dependence of the thermal conductivity of chemical-vapor-deposited diamond Naira M. Balzaretti,a) Albert Feldman, and Edgar S. Etz National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Roy Gat Coatings Technology Solutions, Inc., Somerville, Massachusetts 02143 (Received 17 November 1998; accepted 14 June 1998)
The in-plane thermal diffusivity of chemical-vapor-deposited diamond films was measured as a function of diamond-growth rate. The films, 0.1–0.4 mm thick, were prepared in microwave-plasma reactor at growth rates ranging from 1 to 10 µm/h. A modification of Ångstro¨m’s method was used to perform the diffusivity measurements. The thermal conductivity calculated from the thermal diffusivity shows an inverse relationship with growth rate. Analyses of Raman spectra indicate that both the line shifts and the line widths of the diamond Raman peak are practically independent of the deposition rate, except for the specimen grown at the highest growth rate.
I. INTRODUCTION
Diamond films made by chemical vapor deposition are receiving considerable attention for their potential use as heat dissipating electronic substrates because the films can be made with a thermal conductivity about equal to that of type IIa diamond1 which has the highest thermal conductivity of any material at room temperature. The ability of manufacturers to produce large specimens makes the large-scale use of chemical-vapor-deposited (CVD) diamond in electronic applications very likely. The knowledge of the diamond film thermal conductivity and the dependence of thermal conductivity on process conditions are essential for the further development of thermal applications. Earlier studies have shown that the growth rate of CVD diamond increases with increasing methane fraction in the feed gas2; however, the quality of the diamond as evaluated by the spectral width of the diamond Raman peak and by the strength of Raman peaks associated with nondiamond carbon phases in the films, decreases as the methane fraction in the feed gas increases.3 Furthermore, the thermal conductivity of a film decreases as the methane fraction in the feed gas increases.3 Thus, there is an implied inverse relationship between growth rate and thermal conductivity. More recently, Graebner et al. have measured this inverse relationship.4 The films used in their study had been prepared by microwave plasma
a)
Permanent address: Instituto de Fisica, UFRGS, Porto Alegre, RS, Brazil.
3720
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 9, Sep 1999 Downloaded: 15 Mar 2015
deposition; thicknesses ranged from 2.8–13.1 µm, growth rates ranged from 0.11 to 0.56 µm/h, and thermal conductivities ranged from 1.9–6.0 W cm−1K−1. In this study, we have extended the investigation of the relationship between growth rate and thermal conductivity to CVD diamond films that have been prepared at higher growth rates (1–10 µm/h), which are commercially viable. The films in this study were also thicker
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