Ion beam synthesis of SiC on Si toward the radiation damage free limit

Abstract

Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry in random and aligned to Si 001-channel direction, and Elastic Recoil Detection Analysis (ERDA) techniques were employed to characterize SiC structures obtained by Ion Beam Synthesis. C+ ions at 40 keV were implanted up to a fluence of 2.8 × 1017 cm−2 into a (001) Si substrate capped by a SiO2 layer. Samples with SiO2-cap thicknesses of 110, 190 and 240 nm were compared. For the first two of them, 72% and 11% of C+ ions, respectively, are directly implanted into the Si substrate, however, for the later, no carbon directly reaches the substrate. C+ implantation was performed with samples held at 600 °C and, afterwards, they were annealed at 1250 °C for 2 h under a flux consisting of a mixture of 99% Ar and 1% O2. ERDA demonstrates that C redistribution occurs in the 240 nm SiO2-cap and TEM, Selected Area Diffraction and Channeling revealed an almost continuous cubic and epitaxial SiC layer of about 5–7 nm on the Si surface. This SiC nanolayer presented the optimum crystalline quality, from the standpoint of HRTEM imaging and Channeling results. This synthesis was exclusively based on C migration to the SiO2/Si interface, followed by SiC nucleation during interfacial reconstruction of the crystal structure. The improved quality is justified because the interface is not affected by any implantation damage. On the other end, the synthesis by using the 110 nm SiO2-cap is obtained by direct C inclusion into the Si structure, but also results in epitaxial SiC. The 190 nm SiO2-cap showed, however, a strong regression in the quality: it revealed misaligned grains of SiC immerse in an amorphous narrow layer. Two distinct mechanisms are responsible for SiC synthesis, depending on the cap-layer thickness, and the influence of the radiation damage for each is discussed.