MULTI-FILM STACK ETCHING WITH POLYMER PASSIVATION OF AN OVERLYING ETCHED LAYER

摘要

A method and apparatus for plasma etching a workpiece, such as a semiconductor wafer, including a thin film stack having a top film disposed over a bottom film with an intervening middle film there between. Etch selectivity between the top and bottom films may be as low as between 1:1 and 2:1 and a first carbon-lean gas chemistry is used to etch through the top film, a second carbon-lean gas chemistry is used to etch through the middle film, and the bottom film is etched through by alternating between depositing a polymer passivation on the top film using a carbon-rich gas chemistry and an etching of the bottom film with a third carbon-lean gas chemistry, which may be the same as the first carbon-lean gas chemistry.