Effect of addition of amino acids with hydrophilic side chains to low-concentration H3PO4 for improvement of Si3N4 etching kinetics and oxide regrowth phenomena on multi-layered Si3N4/SiO2 structures

Improvement of Si3N4 etching kinetics and suppression of oxide regrowth phenomena are critical in the selective Si3N4 etching process on multi-layered Si3N4/SiO2 structures for the fabrication of three-dimensional Not AND (3D NAND) devices. To control mass transfer of the solution and the Si3N4 etching by-product, various con-centrations of H3PO4 solutions were used to remove Si3N4 layers of a patterned multi-layered Si3N4/SiO2 structure. It was observed that oxide regrowth was suppressed by reducing the concentration of H3PO4, and 30 wt% H3PO4 produced the highest Si3N4/SiO2 etching selectivity. In addition, amino acids with hydrophilic side chains, such as L-histidine, L-glutamic acid, L-proline, and L-lysine, were introduced into 30 wt% H3PO4. The introduction of amino acids increased the Si3N4 etching rate by providing hydrophilic side chains and polarizing silicon atoms on the Si3N4 surface. Furthermore, the addition of amino acids suppressed oxide regrowth by dehydration of the silanol group of the SiO2-like Si3N4 etching by-product. Finally, Si3N4 could be selectively and uniformly etched in 30 wt% H3PO4 containing amino acids without oxide regrowth on multi-layered Si3N4/SiO2 structures.

Automated summary

The improvement of Si3N4 etching kinetics and suppression of oxide regrowth are crucial in the selective Si3N4 etching process for the fabrication of 3D NAND devices on multi-layered Si3N4/SiO2 structures. By reducing the concentration of H3PO4, oxide regrowth was suppressed and 30 wt% H3PO4 showed the highest Si3N4/SiO2 etching selectivity. Additionally, introducing amino acids with hydrophilic side chains into 30 wt% H3PO4 increased the Si3N4 etching rate and suppressed oxide regrowth.