2010 International Conference on Enabling Science and Nanotechnology (ESciNano), 1-3 December, 2010, KLCC, MALAYSIA

Heteroepitaxial Growth of SiC at Low Temperatures for the Application of a Pressure Sensor Using Hot-Mesh CVD

Kanji Yasuia*, Hitoshi Miuraa, Jyunpei Etoa, Yuzuru Naritaa, and Abdul ManafHashimb•

a Department of Electrical Eng., Nagaoka Univ.ofTechnol. Japan, , b Material Innovations and N anoelectronics Research Group, Faculty of Electrical Engineering,

Universiti Teknologi Malaysia, 81310 Skudai, Malaysia, *Email: kyasui@vos.nagaokaut.ac.jp

Silicon carbide (SiC) is a wide bandgap semiconductor and it exhibits excellent electronic and chemical properties. Fabrication of SiC devices on Si wafers of large diameter is desired to reduce their production cost. For the fabrication of electronic devices in the SiC layer, however, an electronic isolation between SiC and Si substrate is required because of the leakage current between the SiC and the substrate. Therefore the application of the SOl (Si on insulator) technique to the SiC on insulator (SiCOI) structure has been eagerly investigated [1, 2]. SiCOI structure has been investigated for the applications of piezo-resistive sensors and micro electromechanical systems (MEMS) operating at physically and chemically harsh environments [3]. SiC growth on SOl substrates, however, is very difficult owing to thermal instability of the thin top-Si layer. During the thermal annealing of SOl substrates at the substrate temperature lower than 1000°C depending on the top Si layer thickness, Si atoms agglomerate and the Si islands and voids would be formed [4, 5]. Because outdiffusion of the Si atoms into SiC layer is induced in the case of the SiC growth on Si layer, void formation takes place at lower temperatures than that in the case of the thermal annealing. The SiC growth at much lower temperature than 1000°C, therefore, is required. In our previous study, 3C-SiC epitaxial films were grown at 750°C by hot-mesh CVD, a kind of hot-wire CVD which utilizes the catalytic decomposition of source gases by heated tungsten (W) wires with a mesh structure [6], using monomethylsilane (MMS) as a source gas. In this paper, the epitaxial growth of 3C-SiC films on SOl substrates was investigated by the hot-mesh CVD method. And their piezoresistive property was measured for the application of a pressure sensor.

Heteroepitaxial growth of 3C-SiC films on SOl substrates was carried out in a HM-CVD apparatus, as shown in a previous paper [6], using H2 and MMS. SOl substrates with 100nm of top-Si layer and 200nm of buried oxide layer were used. The W mesh (O.lmm diameter, 30meshl inch) was placed above a substrate holder. The flow rate of H2 gas during SiC growth was maintained at 100 sccm. The gas flow ratio of H2 to MMS was approximately 400. Total pressure during SiC growth was 530 Pa. Making a bridge circuit with metallic film resistors, piezoresistive property was measured.

Fig. 1 shows XRD spectra of the SiC films grown on (a) Si and (b) SOl substrates by HM­CVD at substrate temperature of 700-800°C. The W mesh temperature during growth of SiC was kept at 1600°C. In these SiC films on Si and SOl substrates, the (100) oriented SiC crystal was grown at the substrate temperature of 750°C or above. The spectra of SiC on SOl substrates were equivalent to that on Si substrates in the diffraction intensity and in full width half maximum (FWHM).

The cross-sectional SEM images of the SiC/Si interface of SiC films grown on SOl substrates at 800°C and 750°C are shown in Figs. 2 (a) and (b), respectively. The SiC/Si interface of the SiC film grown on the Si is void-free and smooth, as shown in Fig. 2 (b). The SiC growth at substrate temperature of 750°C did not induce the formation of voids in the top-Si layer. At the SiC/Si interface, on the other hand, many voids are observed as shown in Fig. 2(a). Even at the low temperature of 800°C, the diffusion of the Si atoms in the top thin Si layer (100nm) could not be prevented, different from the results of the thermal annealing [5). At the initial growth stage of SiC on Si, the outdiffusion of Si stoms from the substrate is enhanced [8]. The difference between the case of the SiC growth and that the thermal annealing in ultra high vacuum would be

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2010 International Conference on Enabling Science and Nanotechnology (ESciNano), 1-3 December, 2010, KLCC, MALAYSIA

due to the presence of carbon atoms in MMS molecules. However, void free SiCOI structure was thus successfully fabricated using hot-mesh CVO at 750°C.

For the application of piezoresistive sensors, gage factor (OF) was evaluated using a bridge cuicuit shown in Fig. 3. Fig. 4 shows the variation in the resistivity of the SiC layer in SiCOI structure, respectively. From the variation in the resistivity, OF was estimated to be -27. This value is approximately the same as that (OF=-31.8) a SiC epitaxial film on Si(100) grown at 1360'C using atmosphere pressure CVO[9].

Reference

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[2] L. Di. Cioccio, F. Letertre, Y. Le Tiec, A. M. Papon, C. Jaussaud, M. Bruel, Mater. Cs. & Eng., B46, 349, 1997

[3] M. Mehregany, C. A. Zorman, N. Rajan, C. H. Wu, Proc. IEEE, 86, No-8, 1594, 1998.

[4] Y. Ono, M. Nagase, M. Tabe and Y. Takahashi, Jpn. 1. Appl. Phys. 34, 1728-1735, 1995

[5] B. Legrand, V. Agache, 1. P. Nys, V. Seze, D. Stievenard, Appl. Phys. Lett. 76, NO.22, 3271-3273, 2000

[6] Y. Narita, K. Yasui, J. Eto, T. Kurimoto, T. Akahane, Jpn. 1. Appl. Phys., Part 2,44, NO.25, L809 - L811, 2005

[7] K. Yasui, J. Eto, Y. Narita, M. Takata, T. Akahane, Jpn. 1. Appl. Phys., 44, No. 3, 1361-1364,2005

[8] T. Fuyuki, T. Hatayama, H. Matsunami, phys. stat. sol. (b) 202, 359-378, 1997

[9] 1. S. Shor, D. Goldstein, A. D. Kurtz, IEEE Trans. Electron Devices, 40, No.6, \093,993

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