Diffusivity of Si in the 3C-SiC buffer layer on Si(100) by X-ray photoelectron spectroscopy
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1246-B07-10
Diffusivity of Si in the 3C-SiC buffer layer on Si(100) by X-ray photoelectron spectroscopy W.-Y. Chen1, J. Y. Lin1, J. Hwang1* and C.-F. Huang2 1
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan. 2
Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan.
ABSTRACT A void free 3C-SiC film grown on Si(100) can be achieved by low pressure chemical vapor deposition using the modified four-step method. The diffusion step plays an important role to enhance the quality of the 3C-SiC buffer layer on Si(100). X-ray photoelectron spectroscopy was used to characterize the bonding characteristics of the 3C-SiC buffer layer of about 10 nm thick. The Si-C bonds are partially formed on the as-carburized Si(100) before the diffusion step. The ratio of C-C to Si-C bonds on the as-carburized Si(100) is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350 oC for 5 min or at 1300 oC for 7 min. According to XPS data and Fick’s second law, the diffusivity of Si across the 3C-SiC interlayer are determined to be 2.2x10-16 cm2/s and 3.13x10-16 cm2/s at 1300 oC and 1350 oC, respectively. The derived activation energy is 1.6 eV for the diffusion of Si atoms in the 3C-SiC buffer layer. INTRODUCTION Silicon carbide (SiC) is a wide band gap semiconductor for high power and high frequency devices due to its excellent thermal and electrical characteristics.[1,2] Single crystalline SiC in 4H and 6H polytypes are expensive and commercially available for device fabrication. Heteroepitaxy of high quality 3C-SiC on Si has attracted attention in the past decades due to lower production cost. However, the large lattice-mismatch (~20%) and difference in thermal expansion coefficients (~8%) between 3C-SiC and Si are the major problems to overcome in heteroepitaxy. In 1983, Nishino et al. firstly introduced the buffer layer formation in the growth of 3C-SiC on Si. A conventional three-step method, consisting of cleaning, carburization and growth, was illustrated.[3] The carburization step plays two roles in the growth of 3C-SiC on Si. One is to supply carbon atoms in a form of amorphous carbon onto Si at carburization temperature, usually at 1250 oC for the C3H8/H2/SiH4 system. The other is to form a 3C-SiC buffer layer by driving Si atoms out of the Si substrate into the amorphous carbon layer. The buffer layer formation has become a standard procedure for the growth of 3C-SiC on Si since
then.[4-6] In 2008, we developed the modified four-step method (clean, carburization, diffusion and growth) by inserting a diffusion step and removing the cooling step in the conventional three-step method.[7] A void-free 3C-SiC film of high quality was grown on Si(100) in a mixed gas of SiH4-C3H8-H2 using low pressure chemical vapor deposition (LPCVD). The quality of the 3C-SiC buffer layer was improved by introducing the diffusion step in the modified four-step method.[7,8] This is supported by the X-ray diffraction (XRD) spectra from the thicker 3C-SiC
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