Thin SiC layers have been grown by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) on silicon (100) substrates. Growth processes have been performed at low substrates temperatures of 850degreesC and low pressure (mTorr). SiH4 and CH4 were used as precursor gases, added to a continuous Ar flow that maintains a stable plasma all over the process. During the processes, one or both precursor gases were pulsed in order to perform a layer-by-layer growth. Different conditions and flow ratios have been used, while maintaining the microwave power fixed. Previous carbonization of the silicon surface has been also investigated and the presence of a plasma during this step is discussed. Composition and effective thickness of the samples have been determined by FTIR and spectroscopic ellipsometry. Scanning atomic force microscopy (AFM) measurements reveal the presence of ordered microcrystals under certain process conditions of carbonization and growth. These crystals with an apparent cubic structure have average height and diagonal length of about 16nm and 330nm respectively, from the focused analysis of one of them. Its density seems to be related to the carbonization pre-process.