Preparation Of Diamond Films And Its Application Of Improving Thermal Property Of Power Devices

Polycrystalline diamond films with preferred orientation by adopting assisted-bias HFCVD technique are prepared, and the mechanisms of the nucleation and growth of the films are studied. In addition, application of the film to the heat sink of power electron device is discussed.We combined the CVD technique with the PECVD technique by adding a DC or Rf electric field to the reacting region of CVD device, and improved the inputting method of reaction gases, then had executed a diamond film growth system. The advantages of our system are: (1) Reaction power, which can enhance the density of the plasma in the reacting region, is supplied with the heat filament and the DC electric field, or with the heat filament and the RF electric field Both of them can be controlled precisely and they are complementary to each other. (2) The distribution, flux and flowrate of the gases are exactly under control.In order to grow high-quality diamond film on Si substrate, The quality of diamond film on a mirror-polished single-crystal Si surface is examined experimentally, and the enhancement mechanisms of positive or negative bias on nuclear formation is interpreted theoretically. The optimum technological parameters of the nucleation of diamond on the Si surface are studied which can be summarized as follows: the gas flow ratios of CH4/(H2+CH2) and N2/(CH4+N2) is 2% and 15% respectively, the heat filament temperature is 1950 , the substrate temperature is 800 , the total gas pressure is 5.0 103Pa, RF power 100W, and so on. Moreover, by adjusting the technological parameters, polycrystalline diamond films grown preferentially along the different crystal orientations can be prepared.The diamond films are characterized by XRD, TEM, SEM, XPS, AES, and LRM methods. Theresults of XRD and TEM analysis indicate that the films are diamond films, whose crystal state is greatly affected by the technological parameters. The AES result makes clear that the vertical distribution of C atom in the film is very homogeneous, and the purity of C atom in the film is very high. By being tested with ellipsometricy, the refractive index of the diamond film in 632.8 nm wavelength is 2.40~2.71. The heat conduction of the diamond film measured with the photothermal deflection (PTD) method is 4.94~7.85 W/cm K, which is strongly affected by the growth orientation of the diamond grains. The resistivity of the films is 3.63 107~1.32 1012 -cm, and Vickers hardness (HV) is 6849.7-9485.5 kg/mm2.The diamond film is grown on the horizontal power diodes as their heat sink. A heat conduction model of the device is built and simulated with computer, the simulation results coincide with the experimental results quite well, both of them conclude that the working temperature of the diodes is reduced notably as the result of high thermal conductivity of the diamond film.