A technique to reduce charge buildup causing gate-oxide deterioration during biased electron cyclotron resonance (ECR) plasma deposition has been developed. For SiO2 planarization and filling techniques, it is necessary to resolve the charge build-up phenomenon with the biased ECR plasma system. The deterioration is reduced by adjusting the magnet-coil position in the ECR plasma system which means minimizing the magnetic-flux density at the specimen surface.