Processing of workpieces using deposition process and etch process

A method for processing a workpiece, the workpiece comprising a high aspect ratio structure, the high aspect ratio structure comprising a plurality of silicon nitride layers and a plurality of silicon dioxide layers arranged in an alternating fashion, the method comprising:

• placing the workpiece in a processing chamber, the processing chamber located downstream from a plasma chamber for generating a plasma, wherein the processing chamber is separated from the plasma chamber by a separation grid;
• flowing CF4 at a flow rate of about 20 sccm to about 200 sccm, CH4 at a flow rate of about 20 sccm to about 200 sccm, O2 at a flows rate of about 500 sccm to about 1500 sccm, and N2 at a flow rate of about 100 sccm to about 500 sccm into a plasma chamber to form a deposition process gas;
• generating a deposition plasma in the plasma chamber from the deposition process gas;
• filtering the deposition plasma via the separation grid to generate a filtered deposition mixture;
• exposing the workpiece to the filtered deposition mixture, wherein the filtered deposition mixture deposits a passivation layer on a surface of each of the silicon dioxide layers, wherein the passivation layer comprises a fluorocarbon polymer, a hydrofluorocarbon polymer, a slat ammonium silicon fluoride salt, or a combination thereof;
• generating an etching plasma in the plasma chamber;
• filtering the etching plasma via the separation grid to generate a filtered etching mixture;
• and
• exposing the workpiece to the filtered etching mixture, wherein the filtered etching mixture removes at least a portion of the plurality of silicon nitride layers laterally at an etch rate that is greater than an etch rate of the plurality of silicon dioxide layers.