Oxide regrowth mechanism during silicon nitride etching in vertical 3D NAND structures

Abstract It is essential to selectively etch Si3N4 in the presence of SiO2 during the process of fabricating vertical 3D NAND structures. SiO2 etching inhibitors can be added to H3PO4 to increase Si3N4-to-SiO2 etch selectivity; however, the addition of SiO2 etching inhibitors to H3PO4 generates oxide regrowth issues on the SiO2 etch stop layers of the Si3N4/SiO2 pair-layer stacks. It is also observed that generation rate of Si3N4 etching byproduct as well as addition of SiO2 etching inhibitor strongly affects oxide regrowth behavior on the Si3N4/SiO2 multipair-layered structure. In addition, the limited mass transfer of Si3N4 etching byproduct produced heavier amounts of oxide regrowth on the corners of the SiO2 etch stop layers and at the stack structure bottoms. Modification of surface reactivity and the adhesion properties of silica-like monomers on the SiO2 etch stop layer may be important factors for reducing oxide regrowth during the selective etching of Si3N4.