Development for high-aspect-ratio hole etching with hydrogen fluoride gas based cryogenic process

We demonstrate a novel plasma process capable of etching the ONON (silicon oxide/silicon nitride) hole structure for manufacturing 3D-NAND devices with a depth beyond 10 μm and an aspect ratio of approximately 100. The process utilizes hydrogen fluoride (HF) and a phosphorus-containing gas under cryogenic conditions in a dual-frequency capacitively coupled plasma chamber. To investigate the plasma-surface interactions at cryogenic temperatures, we performed in situ quadrupole mass spectroscopy measurements and density functional theory calculations. We found that the surface co-adsorption of the H2O by-product and the HF etchant at cryogenic temperatures and the additional enhancement of H2O adsorption by phosphorus-containing species produced from admixing a few percentage of a phosphorus-containing gas are key factors to enhancing the etch rate. This novel process has achieved dramatic productivity improvement compared with conventional fluorocarbon-based plasma etching processes, thus enabling the formation of ultra-high-aspect-ratio etching features for next-generation semiconductor device manufacturing.