The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH4-CO2 by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH4-CO2 gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant "cage-like" structure with completed (100) facets. This result indicates that the continued addition of nitrogen gives rise to the deterioration of (111) facets and the retention of (100) facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C-2 emissions in the gas phase under optimum conditions.