Nanotech 2010

The Growth of Nano Crystalline Diamond in Silicon Substrate Using Different Etching Gasses by HFCVD

Z. Khalaj, M. Ghoranneviss, S. Nasiri Laheghi, P. Pedram
Islamic Azad University, IR

Keywords: nano crystalline diamond, etching gasses, HFCVD

Abstract:

Diamond nano crystals are in great demand for electrical, optical and mechanical applications due to their excellent properties. Among the various techiniques for growing diamond nano structures, the Hot Filament Chemical Vapor Deposition (HFCVD) is one of the most common methods due to its low capital cost and allows the diamond deposition in a simple way, overcoming some of the limitations of the other more sophisticated CVD techniques [1]. The HFCVD system is manufactured by our group (shown in Fig.1), used in this study for growing diamond nano crystals. The silicon wafers coated with gold(Au) with 13nm thickness is used as a substrate for growing diamond nano crystals with (111) structure. A typical Rutherford back scattering spectrum of Au thin film’s thickness is given in figure2. The Atomic Force Microscopy (AFM) analysis shows the roughness of the substrate after coating with gold (Figure 3). To avoid the substrate oxidation, the reaction chamber is evacuated to 10-6 Torr as a base pressure. After getting this base pressure, the substrate tempreture is increased up to 550°C, gradually. For etching the substrate, N2 gas is fed into the reaction chamber. At this time the temperature of the filament is increased up to 1600°C. This operation is performed at 10 Torr as the etching pressure and for 45 minutes. A combination of CH4/H2 with 5% flow ratio is fed into the reaction chamber. The reaction pressure and tempreture of the filament for the growth are 30 Torr and 1800°C, respectively. The time taken for the growth is 60 minutes. In other cases, the same conditions are used, except the etching gasses which are NH3 and H2. Figure 4 shows XRD patterns of NCDs. It can be seen that the patterns exhibit a peak at 2 =44.5 only for the sample etched by H2, which indicates the diffraction from (111) diamond structures. One of the best factors for crystallite quality is Full-Width-Half- Maximum (FWHM) of the XRD patterns. In fact, Sharp peaks with small FWHM indicate high crystal quality. The XRD patterns of these samples show that the diamond nano crystals (111) etched by H2 have sharp and clear peaks (see Fig.4,a). On the other hand, for the case of NH3 as the etching gas, the results do not show any type of growth for diamond nano crystals (Fig4.b). However, when we have used N2 as etching gas, diamond nano crystals with (311) structure are only observed (Fig.4,c). Figure 5(a,b) shows the Scanning Electron Microscopy (SEM) images of high density diamond nano crystals employing H2 as etching gas at 1600°C filament temperature. The average size of these NCDs are 118nm (see Fig.5,b). Figure 5(c,d) shows the SEM images of the nano crystalline diamond films after the etching by N2 at the same condition. According to Scherrer formula, the grain size (T) of diamond nano crystals were calculated by T=0.9/(2 ) cos, where (2 ) is the FWHM in radians and  is the wavelength in nm [2]. Further the calculated particle size for the diamond nano crystals are grown on the Si substrate using H2 and NH3 as etching gas was less than 50 nm (Table 1).
 
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