Etching narrow deep holes in vertically stacked 3D NAND flash memory made 2X faster by using plasma including hydrogen fluoride

https://www.eurekalert.org/news-releases/1071780

"holes in alternating layers of silicon oxide/ silicon nitride...plasma source of high-energy ions... keeping wafer semiconductor to be processed at low temperature... hydrogen fluoride gas creates plasma for cryo-etching at 640 nm per minute... improved etching quality... 4X etch rate by adding phosphorus trifluoride (only marginal increase with silicon nitride)... ammonium fluorosilicate slows etching, but water can offset this effect by weakening ammonium fluorosilicate bonds/ lowering temperature, accelerating etching"