High-quality silicon dioxide films have been deposited at 130 degrees C by a sputtering technique using an electron cyclotron resonance microwave plasma. Film properties have been studied as a function of O-2 flow rate in the range of 2-8 seem with a constant Ar flow rate of 8 sccm when other plasma conditions were a microwave power of 700 W, and a radio frequency power of 700 W supplied to a target for sputtering. Dielectric breakdown characteristics have been investigated by ramp current-voltage measurements. Films deposited with an O-2 flow rate of 5.3 sccm have a dielectric breakdown field of 10 MV/cm, which is close to that of thermally grown silicon dioxide film. The deposition rate was as high as 23 nm/min. Structural properties of films have also been characterized by ellipsometry and infrared absorption spectroscopy, showing that films with O-2 flow rates above 4 sccm have near-stoichiometric composition.