Method for roughness improvement and selectivity enhancement during arc layer etch via adjustment of carbon-fluorine content

A method of patterning a layer on a substrate, comprising:

• disposing a substrate comprising a multi-layer mask in a plasma processing system, wherein the multi-layer mask has a patterned layer defining an open feature pattern overlying a silicon containing ARC (anti-reflective coating) layer;
• establishing a flow of a process gas to the plasma processing system, the process gas containing:
• a first gaseous molecular constituent composed of C, F and optionally H, and having a carbon-to-fluorine ratio of 1-to-4, and
• a second gaseous molecular constituent composed of C, F, and optionally H, and having a carbon-to-fluorine ratio of 1-to-3,
• selecting a process condition that adjusts the C-F molecular ratio to increase an etch selectivity, measured as the ratio of the etch rate of the silicon containing ARC layer to the etch rate of the patterned layer, to a value that exceeds 5-to-1 by selecting a ratio of the flow rate of the first gaseous molecular constituent to the flow rate of the second gaseous molecular constituent greater than or equal to 0.5 and less than 2.5;
• igniting plasma from the process gas using a plasma source in accordance with the process condition;
• and
• exposing the substrate to the plasma to extend the feature pattern of the patterned layer into the silicon containing ARC layer.