Deposition of epitaxial silicon carbide films using high vacuum ...

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8 D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12 Fig. 1. X-Ray diffraction patterns of SiC thin films grown on Si(100) substrates using DEMD at various deposition temperatures and times given in the figure. substrate was mounted on a stainless holder that was heated by DC power supply. The general CVD condition y7 y5 was pressures between 2.0=10 Torr and 1.0=10 Torr and growth temperatures of 700–1000 8C, respectively. The substrate temperature was measured with an optical pyrometer. The deposition time was lasted to be maximum 6 h and SiC films have been grown on both Si (100) and SiO patterned Si (100) substrates. 2 The diethylmethylsilane (DEMS), (CH CH ) 3 2 2 –SiH–CH , used in this study as single precursor, is a 3 liquid at room temperature with boiling point of 78 8C. This makes the handling aspects much more simplified compared with conventional dual-source CVD. Also, the use of single precursor insures stoichiometry, hence, it eliminates the need for an elaborate gas handling system. After deposition, a number of analysis and characterization techniques were employed to investigate the deposited SiC films. These include X-ray Photoemission Spectroscopy (XPS) to confirm chemical composition, X-ray diffraction (XRD) to determine structural crystallinity, and Atomic Force Microscope (AFM) to investigate SiC film topology. Scanning electron microscopy (SEM) was also used to investigate the SiC film morphology and the quality of the SiCySi interface as well as to estimate film thickness by cross-sectional image. 3. Results and discussions Fig. 1 shows the X-ray u–2u diffraction patterns of cubic SiC thin films grown on Si (100) surface at temperatures in the range 700–1000 8C and 1.0=10 y5 Torr for different deposition time. Fig. 1a shows the XRD pattern of SiC thin film grown at 700 8C and 2 h. From Fig. 1a b, we can see that SiC thin film (1a) grown at 700 8C and 2 h has an amorphous structure. However, with increasing the deposition time to 4 h at the same temperature, the diffraction pattern shown in the Fig. 1b shows a crystal structure with (200) 3C– SiC plane (2us41.48) as well as the graphite carbon structure (2us45.28). This indicates that with single precursor MOCVD crystalline 3C–SiC film can be deposited at much lower temperature than conventional CVD. With increasing the deposition temperatures from 700 to 900 8C, moreover, a significant increase of the intensity of 3C–SiC (002) diffraction peaks was observed, showing an improvement of crystallinity. The XRD pattern (see Fig. 2c) of 3C–SiC thin film grown at 900 8C exhibits a very large and sharp peak at the (200) reflection of 2us41.48. This indicates that this thin film was grown epitaxially and may have a monocrystalline nature with (200) preferred orientation. However, in the Fig. 1d, small peaks attributed to the 3C– SiC(111) diffraction also appeared in addition to major
D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12 9 Fig. 2. SEM images of SiC thin films grown on Si(100) substrates using DEMS at various deposition temperatures. peaks of 3C–SiC (200) diffraction, indicating that polycrystalline 3C–SiC thin film was obtained at deposition temperatures of 1000 8C. From our XRD data, with increasing the deposition temperature from 700 to 900 8C, high quality 3C–SiC layer was obtained under the same deposition conditions. The XRD results also show that the deposition time as well as deposition temperature could be one of the important factors for influencing the film crystallinity. Fig. 2 shows surface morphology changes of the 3C– SiC films grown at various temperatures (700–1000 8C) for 2 h under the same deposition pressure of 1.0 y5 Torr=10 Torr, respectively. We can see that the film grown at 700 8C has a smooth surface and nano size SiC crystals as shown in the Fig. 2a. With increasing the deposition temperature, 3C–SiC film with relatively large crystals were deposited. The surface morphologies of the films grown at 900 and 1000 8C show much larger crystal size than those of the films grown at 700 and 800 8C. The SEM image of SiC film grown at 800 8C shown in the Fig. 2b exhibits a crystal shape of SiC crystals with sub-micron size. Above 800 8C, the crystal size and crystallinity of the 3C–SiC films are apparently limited to the substrate temperature. Especially, from the Fig. 2c, we can see that the major crystal form of a deposited film grown on the substrate at 900 8C is rectangular in shape. We also confirm the crystal form of the SiC film deposited at 900 8C from a AFM result (see Fig. 4a,c). However, a polycrystalline shape with relatively larger crystal size can be seen in Fig. 2d, when the growth temperature was at 1000 8C. This is in good agreement with the XRD result shown in the Fig. 1d. Film stoichiometry of the 3C–SiC film with optimized expitaxial crystal structure was determined utilizing the XPS analysis. The survey spectrum of Fig. 3a clearly shows the photoelectron peaks of Si 2s, Si 2p, C1s and C (KLL) Auger signals indicating formation of silicon carbide film. Oxygen (O 1s) can be attributed to surface contamination by moisture during sample transfer in the air condition. Also, we could see that the carbon content decreased after the Ar ion sputtering as shown in the Fig. 3c. As the sputtering depth is less than 3 nm, the carbon is the adsorbed species on the SiC surface. The reason for arising the carbon content on the surface is mainly due to the air contamination after deposition. In Fig. 3b, the Si 1s high-resolution spectra obtained before and after Ar ion sputtering are also shown. To compare the change of Si 1s binding energies for the SiC film before and after Ar ion sputtering, the Si 1s peak at 100.9 eV obtained without Ar ion sputtering is shifted to lower binging energy at 100.3 eV after Ar ion sputtering. The reason for this binding energy shift is due to increasing of carbidic after removing of graphite carbon and surface SiO x species by Ar ion sputtering. However, we also see weak carbon shoulder peak in Fig. 5c but if we did more Ar ion sputtering the graphite carbon can be
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