Etching methods for reducing micro and macro scalloping on sidewalls of etched features of semiconductor devices

A method for patterning a material layer on a substrate, comprising:

• forming a hard mask layer on a material layer disposed on a substrate, the material layer comprising a plurality of first layers and a plurality of second layers alternately formed over the substrate;
• performing a first etch process to form features in the material layer through the hard mask layer by supplying a first etching gas, wherein the first etch process etches the plurality of first layers at a first etch rate and the plurality of second layers at a second etch rate to form a plurality of protrusions and a plurality of recessions on a sidewall of the features;
• performing an oxidation process to oxidize a sidewall of the features by supplying an oxidation gas and forming an oxide layer, wherein a first side the oxide layer adjacent the plurality of protrusions and the plurality of recessions is conformal to the plurality of protrusions and the plurality of recessions;
• and
• performing a second etch process on the oxide layer to etch a second side of the oxide layer by suppling a second etching gas, the second side being planar and opposite the first side, wherein a difference between a maximum thickness and a minimum thickness of the oxide layer is about 1 nm to about 2 nm after performing the second etch process.