Selective plasma etching for contact holes using a fluorine-based chemistry with addition of N2

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 °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.