We studied the misorientation angle dependence of the surface morphology in homoepitaxial diamond film grown by the microwave plasma chemical vapor deposition (CVD) method using an extremely low CH4 concentration gas system (less than 0.15% CH4/H-2 ratio). We found that, for a misorientation angle (theta(off)) of less than 1degrees, the surfaces of diamond films are atomically flat surface. Their mean roughness (Ra) determined by atomic force microscopy (AFM) is less than 0.04nm. Ra subsequently increases as theta(off) increases above theta(off) > 1.5degrees. This tendency is opposite to that of the conventional homoepitaxial growth using a high CH4/H-2, ratio. We also found that the theta(off) dependence of Ra of surfaces formed by hydrogen (H-2) plasma etching has & same tendency as that of the CVD growth at the low CH4/H-2 ratio mentioned above. Specifically, Ra is less than 0.17 nm for theta(off) < 1degrees and increases as theta(off) increases. These experimental results suggest that the surface morphology of the homoepitaxial CVD diamond films grown at low CH4/H-2 ratios is mainly determined by the H-2 plasma etching process that strongly depends on the theta(off) of the diamond substrate. (C) 2002 Elsevier Science B.V. All rights reserved.