Behavior of oxide regrowth during the selective Si3N4 etching process on 3D NAND structures using finite element computational simulations

Abstract

Oxide regrowth should be suppressed during the etching of silicon nitride, which is used to fabricate three-dimensional Not AND (3D NAND) devices. This requires a detailed understanding on the mass-transfer characteristics of Si3N4 etching byproducts that cause oxide regrowth. Finite element method (FEM) simulations are performed to investigate the mass transfer of Si3N4 etching byproducts (EBSi3N4) and oxide regrowth during Si3N4 etching on a 3D Si3N4/SiO2 multistack. In particular, the concentration profiles of the byproducts under various etching conditions, such as different numbers of Si3N4/SiO2 multistacks, diffusion coefficients of the byproducts, etching rates of Si3N4, and initial concentrations of Si-based additives, are monitored. Furthermore, the in-situ generation of oxide regrowth under various etching conditions is evaluated. Consequently, an increase in the diffusion coefficient of the byproducts is proposed as the most promising method for suppressing oxide regrowth during Si3N4 etching on high-numbered 3D NAND stacks. The FEM simulation results are strongly supported by data from Si3N4 etching experiments on Si3N4/SiO2 multistacks.