Boron-doped polycrystalline diamond with both (100) and(lll) facets were grown by microwave plasma chemical vapor deposition with and without oxygen (O-2) to Study effects of O-2 On surface morphology, crystal quality, and boron-doping concentration of the films. It was found by Raman spectroscopy that the addition of O-2 improved the film quality as evidenced by the decrease of both the full width at half-maximum of the 1333 cm(-1) diamond peak and the background level. By the addition of 0.10-0.25% O-2, the boron concentrations in the diamond decreased to the same extent by two orders of magnitude for both (100) and (111) facets, indicating that the oxygen is playing a role in the gas phase in suppressing the involvement of diborane. It was also observed by scanning electron microscopy that the (100) facets of the diamond grown with O-2 appeared darker than the (111) facets, while the opposite is the case for the films grown without O-2. This is because the secondary electron emission was suppressed by a higher concentration of terminating species on the (100) facets as compared to the (111) planes, indicating the added oxygen is also affecting the chemistry of the diamond surface.