Selective oxide trench etch for dual damascene process in a transformer coupled plasma system

The characteristics of oxide trench etch in a dual damascene process were studied in a transformer coupled plasma etcher using C/sub 4/F/sub 8//CH/sub 2/F/sub 2//CO mixed plasmas. It was found that the selectivity of oxide with respect to nitride is inversely proportional to the DC bias voltage measured in the C/sub 4/F/sub 8/ plasma system. However adding CO gas to C/sub 4/F/sub 8/ plasma caused an increase in the selectivity with increasing DC bias voltage, which possibly resulted from the reduction of ion densities by the reaction of CO with fluorine ions in the plasma. Under the optimized trench etch conditions with low DC bias voltage, a dual damascene structure of 0.18 /spl mu/m design rule was successfully constructed.