Thermal conductivity of diamond films deposited at low surface temperatures
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S. Chattopadhyay and K.H. Chen Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan 106, Republic of China (Received 7 March 2006; accepted 25 May 2006)
Polycrystalline diamond films are deposited on p-type Si (100) and n-type SiC (6H) substrates at the low surface deposition temperatures of 370 °C–530 °C using a microwave plasma-enhanced chemical vapor deposition system in which the surface temperature during deposition is monitored and controlled. A very high growth rate up to 1.3 m/h on SiC substrate at 530 °C surface temperature is obtained. The room temperature in-plane thermal conductivity of the low-surface-temperature–deposited thin films is measured by a traveling wave method. The diamond films of grain sizes between 3 and 7 m and deposited at 370 °C showed a high thermal conductivity value of ∼6.5 W/cm-K, which is much higher than the single crystal SiC thermal conductivity value at room temperature. Diamond films deposited on Si and SiC single crystals at higher temperatures showed even higher thermal conductivities of 11–17 W/cm-K. The structure and microstructure of these films are characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy, and are related to measured thermal conductivities.
I. INTRODUCTION
High room temperature electrical resistivity (>10 ⍀cm), thermal conductivity (15–20 W/cm-K), and low coefficient of thermal expansion (≈10−6) make chemical vapor deposition (CVD) diamond an attractive material for use in the thermal management of electronic devices. Heat spreading and removal is a major problem for device reliability and performance in advanced electronic packages using high-power and high-speed chips. Heat removal and management become even more important for advanced very large scale integration (VLSI) and surface mount technology using the multichip modules because of increased packing density of the integrated circuits (IC) chips and system performance.1 Outstanding thermal and electronic properties of CVD diamond make it more attractive for thermal management applications as substrates and heat spreaders than the conventional materials such as Si, Al2O3, AlN, GaAS, SiC, BeO, and glass/ceramics. However, the high thermal conductivity of synthetic diamond alone is not sufficient to dissipate the heat, as the heat capacity of diamond is not large. Therefore, the electronic packaging industry uses 13
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0286 J. Mater. Res., Vol. 21, No. 9, Sep 2006
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diamond heat spreaders along with a high heat capacity substrate such as Cu, Mo, or Si3N4 as heat sink, which in turn may be cooled by solid, liquid, or vapor coolants. Thermal conductivity of diamond thin films depends on the processing techniques and microstructure such as crystallite size, purity, and grain boundary structure. Diamond films synthesized by CVD show anisotropic thermal conductivity, with the larger conductivity
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