Etch characteristics of maskless oxide/nitride/oxide/nitride (ONON) stacked structure using CHF-based gas.

Oxide/Nitride/Oxide/Nitride (ONON; SiO/SiN/SiO/SiN) stacked structure is widely used in the 3D vertical structure of semiconductor cells. Previously, to form a 3D cells, photoresist (PR) was patterned and repeatedly trimmed on the top of ONON after the etching of one ON layer. Due to the time-consuming process of etching layer-by-layer of ON layer, two-step etch processing using CF-based or CF-based gases composed of maskless ONON stack feature etching and followed one ON layer-by layer etching by PR trimming in the ONON stack feature are employed these days.