Diamond films have been deposited on silicon substrate using reactant gases of methane and hydrogen by electron cyclotron resonance (ECR) microwave plasma chemical vapor deposition system. The deposition was carried out at a low pressure of 2 x 10(-3) Torr and the substrate temperature varied from approximately 600 degrees C to 800 degrees C. The film morphology was examined by scanning electron microscopy (SEM) and the phase was determined using Raman spectroscopy and transmission electron microscopy (TEM). The variation of gas composition over a range of 1-5% has a significant effect on the morphology of coatings. TEM analysis shows that the grain size was about 50-100 nm.