Improvement of Si3N4/SiO2 etching selectivity through the passivation of SiO2 surface in aromatic carboxylic acid-added H3PO4 solutions for the 3D NAND integration

[Display omitted] •Aromatic carboxylic acid added-H3PO4 selectively etched Si3N4 on Si3N4/SiO2 multi-stack.•Loss of SiO2 surface layer is suppressed in aromatic carboxylic acid added-H3PO4.•Electrostatic attraction occurs between aromatic carboxylic acid and SiOx surface.•Aromatic carboxylic acid forms passivation layer on SiOx, suppressing SiO2 etching. Selective Si3N4 etching becomes challenging as the number of stacks in three-dimensional Not AND (3D NAND) flash memory devices increases. To suppress changes in the thickness of SiO2 layers in Si3N4/SiO2 multi-stack structures, etching inhibitors should be added to H3PO4 solutions. Notably, carboxylic acids can be adsorbed on OH-terminated substances, such as SiO2, by forming Si-O-C bonds. Therefore, carboxylic acids added to H3PO4 solutions can be adsorbed on SiO2 surfaces, and passivation layers can be formed, suppressing SiO2 etching. When a Si3N4/SiO2 multi-stack structure is dipped in a H3PO4 solution, the Si3N4 layers are removed, and the SiOxNy surfaces on the SiO2 layers are converted into SiOx surfaces with positively charged oxygen vacancies. For aromatic carboxylic acids, C=O bonds in their carboxyl groups can be converted to C-O-, causing electrostatic attraction between the C-O- groups and oxygen vacancies on SiOx surfaces. Consequently, aromatic carboxylic acids can be adsorbed on SiOx surfaces via the electrostatic attraction and Si-O-C covalent bond formation, creating robust passivation layers and suppressing SiO2 etching. However, aliphatic carboxylic acids form only Si-O-C bonds on SiOx surfaces and hence cannot realize the same functions as their aromatic counterparts.