Kinetic Effect of Additives in High Temperature Phosphoric Acid on the Etching of Si3N4/SiO2

Highly selective etching of Si 3 N 4 to SiO 2 in phosphoric acid is required for the 3D NAND integration. When a single wafer tool is introduced in this process, the process temperature needs to be well controlled. Therefore, the effect of various additives in phosphoric acid on the kinetics of the Si 3 N 4 and SiO 2 etching reaction were investigated at a higher temperature up to 200 °C in this study. The etching rates of Si 3 N 4 and SiO 2 increased whereas the activation energies decreased with the addition of either HF or NH 4 F. As the concentration of HF is increased, the activation energies of Si 3 N 4 and SiO 2 etching further decreased. On the other hand, Si-containing additives increased the activation energy of SiO 2 etching while the activation energy of Si 3 N 4 etching was unchanged. In general, etching selectivity of Si 3 N 4 to SiO 2 decreased with the temperature of the etchant and the amount of change in the etching selectivity was different depending on the additives in H 3 PO 4 .