keV- and MeV- Ion Beam Synthesis of Buried SiC Layers in Silicon
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Homogenous, epitaxial buried layers of 3C-SiC have been formed in Si(100) and Si(1 11) by ion beam synthesis (IBS) using 180 keV high dose C ion implantation. It is shown that an annealing temperature of 1250 °C and annealing times of 5 to 10 h are sufficient to achieve well-defined Si/SiC/Si layer systems with abrupt interfaces. The influence of dose, annealing time and temperature on the layer formation is studied. The favourable dose is observed to be dependent on the substrate orientation. IBS using 0.8 MeV C ions resulted in a buried SiC precipitate layer of variable composition.
INTRODUCTION
Recently, SiC has attracted much attention as a novel semiconductor material for high frequency, high power applications operating in a high temperature environment. Due to its large band gap, SiC seems to be well suited to develop nonvolatile memories. In addition, the physical strength and its chemical inertness make SiC a favourite future material for membranes in sensor devices. Among the biggest advantages of SiC compared to other compound
semiconductor materials are the compatibility of SiC to pure silicon, the possibility to grow a thermal oxide and the ability to perform n- and p-type doping by ion implantation. Unfortunately, however, the larger application of SiC seems to be limited by the restricted wafer size available and the comparatively high prices of SiC substrates. At present, CVD methods are the standard technique used to grow SiC by homoepitaxy or by heteroepitaxy on Si substrates. For some applications, it might be favourable to have the silicon carbide as a thin film buried in a silicon wafer. Therefore, ion beam synthesis (IBS) of buried SiC layers is studied as an alternative method to grow SiC. Moreover, due to the general ease to scale up ion beam techniques from small to large wafer sizes and due to the possibility to remove a Si capping layer chemically, ion beam synthesis might offer a way of creating seeds for the homoepitaxy of larger SiC crystals. The IBS of buried SiC layers has been studied for more than 20 years [1,2]. Since then, buried layers of other silicon compounds have been successfully grown in silicon by IBS using ion energies in the keV and the MeV region (reviews in [3,4]), but so far, no adequate layers of SiC have been fabricated in silicon. In some early attempts, ion energies were very small, resulting in near-surface carbon profiles [2]. More recent investigations [5-8] have
indicated that SiC layer formation by IBS is hampered by the high temperatures (1405 °C) required to obtain a carbon concentration pile-up into a well-defined buried layer. This has been mainly ascribed to the small diffusivity of carbon in silicon and the stability of defect 171 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
complexes containing carbon [6,8]. For this reason, multiple energy implantation of C ions has been used by some groups [8-10] to form layers of constant carbon concentration (obtain rectangular C depth distributions). Moreover, the use of high implant
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