Modeling Oxide Regrowth During Selective Etching in Vertical 3D NAND Structures

One of the critical processing steps during the fabrication of modern 3D NAND flash memory structures is the selective etching of Si3N4 in the presence of SiO2, which can cause the redeposition of byproducts on the SiO2 layers. We present a physical process model for this phenomenon during etching and apply it to simulate oxide regrowth. The model describes the mass transfer of byproducts with a convection-diffusion equation which is solved on a cell-set volume representation of the etched solution. The simulated results, which combine Si3N4 etching, byproduct mass transfer, and the subsequent redeposition, show excellent agreement with experimental studies for the desired structures.