We have investigated the influence of several growth parameters on the incorporation of doping species in the case of 3C-SiC layers grown by CVD on silicon. This includes nitrogen (both intentional and residual) as well as residual aluminum. All concentrations have been determined by SIMS (Secondary Ion Mass Spectrometry). First, we investigated the effect of the growth temperature, growth rate and C/Si ratio on the doping level of (100) oriented layers. Then, we compared the change in nitrogen incorporation versus nitrogen flow rate for layers grown on (100), (111), (110) and (211) oriented wafers.