A study on the feasibility of a process for making large area diamond, single-crystalline films using a microwave plasma assisted chemical vapour deposition reactor is presented. After choosing the (100) orientation for the seed crystals' top faces, the operating conditions of the plasma reactor were optimised in such a way that step flow mechanism or two-dimensional nucleation mechanism can be favoured. To prevent the development of facets at the crystal edges, (100) orientation was chosen for side faces and step flow growth was favoured. Penetration twins formation has been limited, using low substrate temperature and adding a very low amount of nitrogen in the feed gas. Finally, growth on top of 0.08-0.8 cm(2) mosaics is presented, and the layer grown at the interface analysed.