Growth of device quality epitaxial layers requires precise control of thickness and doping uniformities. Computer simulations can provide growers with the necessary knowledge for improving and optimizing the growth process. In this work, the CVD process is simulated in three dimensions, using a reaction-mass transport model. A simplified quantitative model for the nitrogen incorporation in intentionally doped 4H-SiC samples has been developed and applied to a wide range of process parameters. Different reaction schemes are necessary for the two faces of SiC to account for the different doping incorporation behavior. The simulations are validated by experimental data measured by SIMS with good agreement.