P-SiC films

NANOCRYSTALLINE p-SiC FILMS GROWN BY CAT-CVD WITH PRECARBONIZATION PROCESS... 

Nanocrystalline cubic SiC (P-SiC) films were grown on silicon (100) substrate by catalytic chemical vapor deposition (Cat-CVD) at a temperature as low as 300°C with a pre-carbonization process. To enhance nucleation density of P-SiC, a buffer layer was made by carbonizing the substrate surface. From the comparison between both carbonized sample and non-carbonized sample, the precarbonization process has beneficial effects on the growth of nanociystalline p-SiC films. Mechanistic interpretations are given to explain the carbonization process and catalyzing deposition process. 

There are some reports [7,8] about preparing a-SiC and p-SiC films at low temperature by Cat-CVD and other methods, such as magnetron sputtering and plasma enhanced CVD (PECVD). In order too get high quality p-SiC films, the substrate temperatures are still high (400 600°C). Furthermore, the growth mechanism of P-SiC films by Cat-CVD is not well understood. In this work, by using Cat-CVD with precarbonization process, nanocrystalline p-SiC films were successfully synthesized on Si substrate at the low substrate temperature of 300 C. 

Combined with the pre-carbonization process, nanocrystalline P-SiC films were deposited on (100) silicon by (Cat-CVD) at a low temperature (300°C). From the FTIR spectrum it is found that the carbonized sample is composed of P-SiC component which shows a blue shift, and the XRD patterns show that the grain-size of the carbonized sample is smaller. 

WE Carlos, WJ Moore, PG Siebenmann, JA Freitas Jr, R Kaplan, SG Bishop, PER Nordquist Jr, M Kong, RF Davis Residual donors in P-SiC films. Mater Res Soc Symp Proc 97 253, 1987. 

The decomposition of methyl silane (CH3S1H3) is used to produce an amorphous SiC at 800°C and a crystalline SiC at 900°C.P 1 A two-step growth procedure produces SiC films from hexamethyldisilane and 8% H2/Ar mixture at ambient pressure and low temperature. 

The most common substrates for the growth of cubic P-GaN have been GaAs and 3C-SiC, discussed in Datareviews A7.7 and A7.8 respectively. There have been some structural studies of P-GaN films grown on Si (001) [8] and MgO [1]. The major defects in the cubic material are stacking faults along the 111 planes and perfect edge dislocations at the interface [1,8-11]. 

Mirkarimi P. B., Medlin D. L., McCarty K.F., Growth of cubic BN films on P-SiC by ion-assisted pulsed laser deposition, Appl. Phys. Lett., 66 (1995) pp. 2813-2815. 

Figure 9.22. XTEM image of diamond film deposited on Si using 0.3%CH4/H2, showing the presence of a 50 A-thick P-SiC layer at the interface [203],...

Using the above procedure, Kawarada s group has undertaken a series of detailed experiments on HOD films. In Refs. [249, 250], fairly coalesced diamond films with a thickness of only less than 6 pm were grown for 8 h on P-SiC (100) [251] (which itself had been heteroepitaxially grown on Si), as seen in Figure 11.2. 

The atomic structure of HOD film surface was investigated using electron microbeam diffraction in Ref. [259]. The substrate used was a 500-nm thick P-SiC(lOO) that had been heteroepitaxially grown on Si(lOO) and was tilted about the [1 lOj-axis by 4° from the exact (100) orientation. The thickness of the HOD film was -20 pm. According to the RHEED pattern, using the electron micro-beam (the spatial resolution as observed by SEM was 0.1 pm), the length of the surface dimer rows was 1.5nm, which was significantly shorter than that of the homoepitaxial layer, 7 to 10 nm. 

In Refs. [303-305], the interface structure was also investigated by cross-sectional HRTEM. The diamond films were grown by the three-step process, and the conditions are listed in Table H.3. Consequently, an HOD film was grown in the center of the Si(lOO) substrate. In the carburization step, there was an a-C film of 250-nm thickness on Si, in which p-SiC, diamond, and graphite were embedded. A closer examination indicated that there existed an interlayer of 1.5- to 2-pm thickness between Si and the a-C layer, which was identified as a-SiC [305]. Since the bias voltage is not usually applied uniformly across the Si wafer, the distribution of these materials depended on the location on the Si substrate. Near the edge of the... 

In Ref [311], diamond films were deposited on Si(lOO) substrates by the two-step process using a bell-jar type MPCVD reactor [221]. TEM images showed that hillock structures with a density of 7 x 10 /cm were present at the diamond/Si interface. According to the ED pattern analysis, the hillocks contained p SiC and diamond crystals that were embedded in an amorphous material (carbon). Some P-SiC 220 planes were parallel to Si 220 planes, indicating that some P-SiC particles were in epitaxial relationship with Si. A cross-sectional TEM of the specimen showed that the hillocks of less than lOOnm in height and 50 nm in diameter were formed after the BEN treatment, as seen in Figure 11.25. 

In Ref [315], HOD films were grown using the two-step process based on the BEN technique of Ref [289], and the interface structure was studied by TEM. As a consequence of the BEN process, (i) the carburization of Si created nanocrystalline, heteroepitaxially oriented fi-SiC, (ii) the [3-SiC layer formed nanometer size hillocks and ridges that were aligned parallel to the Si[110] direction, (hi) diamonds nucleated on the 3-SiC layer that was convex, and (iv) P-SiC existed only under the... 

It is of most intrigue that unlike previous nucleation models, this model assumes a formation of diamond nuclei or nucleation sites inside the P-SiC layer, while the p-SiC layer concurrently plays a role of basal lattice for diamond epitaxial growth like in the precedent models. The second point of intrigue is the fact that the exposure and survival of the diamond nuclei or nucleation sites are made possible by a subtle balance of etching rates of Si, P-SiC, diamond, and other forms of carbon. This is consistent with the fact that HOD films can be formed only when the substrate was pretreated by proper BEN conditions. 

In Figure 12.9 (a), (i) there are six 111 diffraction poles, rather than three, around the central (111) pole, and (ii) three diffraction poles, (111), (111), and (111) are more intense that the other poles, (111), (111), and (111). The result (i) indicates that there are two possible orientations of diamond crystals that are rotated by 60° in plane with respect to each other. A similar type of orientational structure has been observed for p-SiC(l 11) epitaxially grown on 6H-SiC(0001) [395]. In this case, incoherent boundaries, called double positioning boundaries, are formed in the film by 60°-rotated domains. On the other hand, the result (ii) indicates that the three orientations, (111), (111), and (111), are preferable to other three orientations. The existence of non-equivalent diamond orientations on the Pt(lll) surface was attributed to interactions with the second nearest neighbor Pt atoms. However, the incoherent boundaries due to the existence of 60°-rotated diamond crystals have not been identified yet. It is of interest that an azimuthally unidirectional surface was formed as the diamond CVD was continued for a longer time, as seen in Figure 12.7 (b). 

Badzian and Badzianl " suggested that diamond nucleation on Si is preceded by the formation of a p-SiC buffer layer, and diamond nucleation occurs on the surface of the carbide. This is supported by many growth experiments of diamond particles or films on Si substrates in HFCVD and... 

Kim et al.f studied the effect of gas pressure on the nucleation behavior of diamond on a Si(lOO) substrate in HFCVD. The pressure was varied from 2 to 50 torr, while a filament temperature of2200°C, a substrate temperature of 850°C, a total flow rate of 20 seem and a CH4 concentration of 0.8 vol.% were used. The characterization of diamond deposits using micro-Raman spectroscopy, SEM and OM revealed that the maximum nucleation density of diamond parades on the unscratched Si substrate occurred at a pressure of 5 torr. The pressure dependence of the nucleation density was explained by the competition effect between P-SiC formation, which increases the diamond nucleation density, and atomic-hydrogen etching, which decreases the nmnber of nucleation sites. On the basis of this finding, a new fabrication approach for high-quality diamond films without... 

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