Both slow positron beam coupled to Doppler broadening spectrometer and fast positron lifetime spectrometer have been used to investigate vacancy defects in the subsurface and in the bulk of three different n doped 3C-SiC monocrystals. These samples have been grown in HOYA company using CVD on Silicon substrates. Measurements show the presence of ionic acceptors and vacancy defects which size depends on the kind of crystals. It appears that the two faces of the crystals are very different : "growth" face contains much less vacancy defects than "substrate" face. The influence of polishing carried out in Novasic Company has also been investigated.