Nanocrystalline Silicon Carbide Film Growth Using Hot Filament CVD
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Si substrates by the same method used for forming porous silicon [4,5]. Unfortunately. these porous SiC faced similar problems as those encountered by porous Si in terms of practical applications. Recently, there has been strong interest in Si based' light emitting materials [6-9], such as hydrogenated nanocrystalline Si films which contain Si nanocrystallites embedded in a matrix of Si nitride or oxide. If nanocrystalline SiC (nc-SiC) films with similar structure can be fabricated, then based on the wide band gap characteristic and quantum confinement effect, it is possible to obtain high efficiency short wavelength light emission. In view of this, the hot filament chemical vapor deposition (HFCVD) technique was used in this work to fabricate nc-SiC films. The structures of these nc-SiC films have been investigated by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) absorption, X-ray phtotoelectron spectrosocpy (XPS) and Raman scattering. The measurements confirmed the formation of nc-SiC in an amorphous SiC matrix for these films. Strong visible emission from these nc-SiC films has been successfully demonstrated at room temperature. EXPERIMENT The samples are deposited in an ultra-high vacuum HFCVD equipment. There is a pair of parallel plate in the chamber, the substrate are secured on the lower side of the upper plate 517 Mat. Res. Soc. Symp. Proc. Vol. 593 ©2000 Materials Research Society
during deposition and heating is achieved through several lamps embedded within the upper plate. The hot filament, which is fixed on the lower plate, is used to decompose reaction gases and assist in heating the substrate. The source gases consisting of methane (100%) and silane (10%) are carried into the chamber by high purity H2. In our previous work [10], 3C-SiC films on Si substrates were deposited using the HFCVD technique with appropriate flow gas ratio, chamber pressure, substrate and hot filament temperature. In that experiment, the structure of the films was noted to depend on the substrate and hot filament temperature. In this work, it is found that by using a temperature lower than that used for the deposition of 3C-SiC films, nc-SiC films containing small grains of crystalline cubic SiC can be obtained. Typical deposition conditions needed are: hot filament temperature of 18001C, substrate temperature of 600'C, gas flow ratio of CH 4 :SiH 4 :H2 =2:l0:40 and deposition pressure of 5.Ox 102 Pa. RESULTS AND DISCUSSION To investigate the microstructure of the sample, the film was stripped from the Si substrate, and then sputtered by Ar' to thin it for HRTEM measurement. Figure 1 (a) shows the HRTEM micrograph. A large number of crystalline grains with dimensions of several nanometers can be seen, within which the atoms are periodically arranged. There is no specific orientation for the crystalline grain and the regions between them consist of irregularly arranged atoms, indicating the presence of an amorphous phase. Figure 1 (b) shows the electron d
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