Characteristics of selective SiO2 etching over Si3N4 in a magnetized inductively coupled high density C4F8 plasma have been investigated as a function of process parameters. The SiO2 etch rate increases with both external de magnetic field (0-15 G) and rf discharge power at a pressure of 1.2 mTorr. For Si3N4, the etch rate also increases with rf power at unmagnetized and weakly magnetized (6 G) plasma conditions, but it decreases with discharge power when the magnetic field is higher than 12 G. At the substrate bias voltage of -100 V, the lowest etch rate of Si3N4 is obtained at two different process conditions namely low power, unmagnetized and high power, magnetized discharges. As the pressure increases, selectivity is degraded severely due to the rapid increase in the Si3N4 etch rate. Resulting selectivities varied from approximately 1:1 to 40:1 without altering the feed gas chemistry. Measurement of fluorine density and CF, CF2 flux incident on the substrate reveal that the improvement of SiO2/Si3N4 etch selectivity is correlated to the rate of change of both CF and CF2 radicals being greater than that of fluorine. It is also shown that the high ion current at sufficiently low fluorine density is important for high selectivity. These results imply that the high density low pressure plasma source is indeed important for the selective etching of SiO2/Si3N4.