FORMING A SEMICONDUCTOR DEVICE USING A PROTECTIVE LAYER

In certain embodiments, a method of forming a semiconductor device includes receiving a substrate having an etch mask layer that includes features for preserving corresponding portions of an underlying hard mask layer to be etched during an etching process. The method includes patterning the hard mask layer using the etch mask layer to gradually form a recess in the hard mask layer, the recess having a depth greater than a width of a top surface of a first feature of the etch mask layer, by performing the etching process. The etching process includes alternating between: depositing, using a first plasma, a silicon-containing protective layer over the etch mask layer and the hard mask layer such that the protective layer covers exposed surfaces of the hard mask layer; and subsequently etching, using a second plasma that comprises oxygen, the hard mask layer to form an incremental portion of the recess.