The effects the addition of nitrogen to a CHF3/CF4/Ar-gas mixture on the selectivity of SiO2 to TiSi2 and Si are reported for a magnetically enhanced reactive ion etch system. The selectivity to TiSi2 is more than doubled by adding 10% of nitrogen to the gas mixture, whereas the same addition lowers the selectivity to Si by more than half. The selectivity to TiSi2 is lowered by a factor of 2 by changing the wafer temperature from 70 to 100 degrees C. The selectivity to Si is not influenced by this change in wafer temperature. This contrasting behavior suggests different etch selectivity mechanisms for SiO2/TiSi2 and SiO2/Si. This is confirmed by x-ray photoemission spectroscopy measurements of the TiSi2 and Si surfaces.