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

Abstract

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 concentrations 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.