Characteristics of selectiveSiO2etching overSi3N4in a magnetized inductively coupled high densityC4F8plasma have been investigated as a function of process parameters. TheSiO2etch rate increases with both external dc magnetic field (0–15 G) and rf discharge power at a pressure of 1.2 mTorr. ForSi3N4, 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 ofSi3N4is 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 theSi3N4etch rate. Resulting selectivities varied from approximately 1:1 to 40:1 without altering the feed gas chemistry. Measurement of fluorine density and CF,CF2flux incident on the substrate reveal that the improvement ofSiO2/Si3N4etch selectivity is correlated to the rate of change of both CF andCF2radicals 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 ofSiO2/Si3N4.