SiC is a promising semiconductor for high-power, high-frequency and high-temperature electronic devices and, additionally, its synthesis on Si could be used as an alternative route for integration of GaN and Si technologies: SiC has been used as substrate for GaN growth. In this work, we report ion beam synthesis of about 40 nm SiC layers by 40 keV C implantation into SiO₂/Si(111) structures. The SiC layer is revealed to the sample surface after final SiO₂ etching. Two distinct methods were carried out: a) by sequential C implantations followed by 1250°C  annealing after each implantation step  (under a flux consisting of a mixture of 99% Ar with 1% O₂) and, b) by single-step implantation followed by the same annealing. Rutherford Backscattering Spectrometry was employed to measure layer composition evolution after each sequential implantation step and annealing. Method a) has also allowed to estimate the minimum C fluence for the synthesis of a SiC stoichiometric layer, after annealing, as about Φ = 2.8 × 10¹⁷ cm^-2. Transmission electron microscopy has shown that single-step implantation, up to the same minimum fluence, results in better structural quality.  The sequential synthesis has shown a rather granular nature.