The magnetic field profile of an electron cyclotron resonance microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. The mobility gap deep defect density ND, deposition rate and light-to-dark conductivity were determined for the a-Si:H films. By variation of the magnetic field profile ND could be altered by more than an order of magnitude, from 1 x 10(16) to 1 x 10(17) cm-3 at 0.7 mTorr and 1 x 10(16) to 5 X 10(17) cm-1 at 5 mTorr as determined by junction capacitance techniques. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration. The data is interpreted as a consequence of silane depletion for highly divergent magnetic field profiles.