A numerical two dimensional model to calculate the deposition uniformity over the whole electrode surface in large area rectangular plasma enhanced chemical vapour deposition reactors is presented. In this model, the three dimensional mass and species continuity equations are averaged over the electrode gap, which is small compared to the lateral dimensions of the plasma reactor, to obtain the two dimensional averaged transport equations. The model was applied to the particular case of silicon nitride deposition by selecting a limited chemistry model, including 8 neutral species and nine gas phase reactions. The results are compared with uniformity profiles obtained in a UNAXIS KAI-I 800 Plasmabox(R) reactor.