Reaction Processes at the Initial Stage of Diamond Nucleation on the Surface of Si(111)
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The thermal behavior of CHx(x=2-3) radicals and H atoms adsorbed on Si(1 11) surface was investigated using high-resolution electron-energy-loss spectroscopy (HREELS), quadrupole mass spectrometry (QMS), and low-energy electron diffraction (LEED). We found that CHx(x=2-3) radicals in the top adlayers of saturate adsorption were not stable, and the loose structures among a few top adlayers broke up completely till 550K. TDMS(thermal desorption mass spectrometry) analysis showed significant desorption of atomic hydrogen, CH 2 and CH 3 . In the region of 550K750K, only H 2 was detected by TDMS, and we speculate that the CHx(x=2-3) species catenate each other, and form a network of hydrocarbon, which is possibly the initial stage of diamond nucleation on Si. This formed network was not stable above 800K, C2 hydrocarbon species were observed after the thermal desorption temperature was over 800K. HREELS measurement demonstrated that no H atoms existed when substrate temperature reached 980K. Compared with the result reported by S.-Tong Lee for diamond(Ref. 12), we conclude that low stability of hydrocarbon species on Si is the dominant reason that results in the difficulty of diamond nucleation on perfect Si surface. INTRODUCTION H, CH.(x=2-3), C2H2 , are the three kinds of the most plentiful particles in the atmosphere of chemical vapor deposition(CVD) of diamond. The study has been carried out in depth for the interaction between H and hydrocarbon radicals in the CVD process of diamond1 ' 2. Recently Z. Lin's group investigated in detail the behavior of C2H2 on the surface of Si(100)with (2x 1) reconstruction, the effect of H atom on the C2H2 adsorbed on Si(100) and their importance on the nucleation of diamond at initial stage3 4 . With AES and QMS(quadrupole mass spectroscopy) of TPD(temperature -programmed desorption) did H. Gutleben research the thermal stability of CH 3 on Si(100) 5 . In any case, AES won't see hydrogen directly and would probably dissociate the molecules being studied. The primary energy of the e-beam of HREELS is only a few eV, it is better to utilize HREELS to study the thermal behavior of CHx(x=2-3) on the surface of silicon. Similar research has not been carried out for Si(1 11) yet. Systematic study for the thermal stability of CH1(x=2-3) and H atom is necessary for understanding the nucleation mechanism of diamond on Si surface. It is well known that diamond is one of the most attractive materials of semiconductor for high temperature, but its high cost impedes the application in the industry of semiconductor. Heteroepitaxial growth on cheap substrates(e.g. Si) of single crystal is an attractive way to manufacture single-crystal film of diamond. Great progress of heteroepitaxial growth of diamond on Si was made by the two groups of Jiang 6 and Wolter 7 in 1992, the FWHM of rocking curve was measured less than 90 for the highly oriented diamond films. Since then, the im rovement on the orientation was achieved step by step, and the FWHM was reduced to 2' already , but the goal of epitaxial
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