Homoepitaxial diamond films prepared under low CH4 concentration conditions (CH4/H-2 < 0.15%) show atomically flat surfaces over the whole area (4 X 4 mm(2)) of the substrate. Using these diamond films, Schottky contacts between Al and the high-conductivity layer near the surface of as-grown film have been successfully made with an excellent uniformity with ideal properties. For example, in the film grown at low CH4 concentration of 0.016% CH4/H-2, the ideality factor (n value) and the barrier heights of the Schottky junctions (phi(b)) were close to unity (n < 1.1) and 1.5-1.6 eV, respectively, for nearly all junctions (> 42 dots) prepared on the same Aim. This result indicates that the quality of the films with atomically flat surfaces over the whole area of the substrate is actually excellent in a viewpoint of chemical stability as well as electrical characteristic.