The influence of negative substrate bias on the crystallinity, morphology, and growth rate of the diamond films deposited using microwave plasma-enhanced chemical vapor deposition in 1% CH4/H2 plasma were investigated. The nanocrystalline diamond films were produced exclusively under the biasing at -250 V. With -50 V biasing, faceted (111) microcrystalline diamond films at higher growth rate than no-bias samples were produced. When the biasing between -100 and -200 V, faceted (100) diamond films with decreasing grain size were favored, and the growth rates were gradually reduced along with the increasing biasing. The results indicate that the etching efficiency of H+ ions is enhanced with the increasing kinetic energy obtained from the increasing bias voltage. On the other hand, CHx+ ions at -250 V biasing would have sufficient energy to perform the ion subplantation model to grow the nanocrystalline diamond films by bias-enhanced nucleation. © 2002 American Institute of Physics.