Optimization of the carbonized buffer layer for the growth of high quality single crystal SiC on Si
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Optimization of the carbonized buffer layer for the growth of high quality single crystal SiC on Si. T. Cloitre, N. Moreaud, P. Vicente*, M. Sadowski, M. Moret and R.L. Aulombard. Groupe d'Etudes des Semiconducteurs, Université Montpellier II, 34095 Montpellier cedex 5, France. * Present address: NOVASIC, Pombliere, 73600 Moutiers, France ABSTRACT Carbonized buffer layers were formed on Si (100) nominally oriented substrates with propane diluted in palladium purified hydrogen in a cold wall vertical reactor. Subsequent SiC layers were grown using silane and propane at atmospheric pressure. The growth temperature was ranging from 1150°C to 1350°C. The layers obtained were characterized by LT photoluminescence, IR reflectivity, X-ray diffraction, micro-Raman on cleaved edges, AFM imaging, and optical microscopy. Drastic influence on the layer surface morphology was evidenced depending on the transition step between the carbonization and the SiC epitaxial growth. As a result, we have developed a carbonization process leading to very high quality 3CSiC films grown at 1250°C. INTRODUCTION The heteroepitaxial growth of 3C-SiC on Si substrates is very attractive due to the availability of large sized Si substrates and the lack of commercially available cubic SiC bulk crystal. The epitaxial growth of 3C-SiC on Si allows to combine the properties of SiC to the feasibility of silicon micromachining. Incidentally, the epitaxy of 3C-SiC on SOI (silicon on insulator) also receives a growing interest [1]. Assuming the above arguments, heteroepitaxialy grown 3C-SiC on Si is a very attractive candidate for the realization of sensors to be operated under harsh conditions. The main problem associated with the heteroepitaxy of 3C-SiC is the large difference in lattice constants (20%) and thermal expansion coefficients (8%). This leads to a high defects density in the SiC layers. In order to partially compensate the lattice mismatch effects, a carbonization process is used to build a buffer layer. The crystalline quality of the SiC layers is improved when using high growth temperature [2]. Unfortunately, the silicon substrate suffers important degradations, resulting in interfacial voids formation. These defects are formed via atomic Si outdiffusion through the SiC layer. The Si outdiffusion is thermally activated and may last as long as diffusion paths, such as grain boundaries, are present in the carbonization and the SiC layers. This interfacial voids formation could be reduced when using low growth temperature (1150°C) at the expense of the crystalline quality of the epitaxial layer [2]. Another drawback coming with a high growth temperature is the degradation of the mechanical properties of the silicon substrate that prohibits the use of micromachining techniques. A compromise has to be found in order to grow good quality SiC layers without degradation of the silicon substrate. In this work, we have optimized the quality of SiC layers by varying independently the carbonization temperature and the growth temperature.
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