Dielectric plasma etch process with in-situ amorphous carbon mask with improved critical dimension and etch selectivity

A plasma-enhanced process is performed in a single plasma reactor chamber for etching a thin film layer on a workpiece, using a hard mask layer including an amorphous carbon layer (ACL) overlying the thin film layer and an anti-reflection coating (ARC) overlying the ACL. The process includes etching a pattern in the ARC in accordance with a photoresist mask overlying the ARC, using a plasma produced from a fluorine-containing process gas, and then removing fluorine-containing residue from the reactor chamber and/or workpiece by performing a first transition step by replacing the fluorine-containing process gas with an inert species process gas and maintaining a plasma in the reactor chamber. A pattern is then etched in the ACL using the ARC as an etch mask by replacing the argon process gas with a process gas containing hydrogen while maintaining a plasma in the chamber. Thereafter, hydrogen-containing residue is removed from the reactor and/or from the chamber by performing a flush step by replacing the hydrogen-containing process gas with argon gas and maintaining a plasma in the chamber. The process continues with etching a pattern in the thin film layer using the ACL as a hard mask by replacing the argon gas in the chamber with a species capable of etching the thin film layer.