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

Abstract

Highly selective etching of Si3N4 to SiO2 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 Si3N4 and SiO2 etching reaction were investigated at a higher temperature up to 200 °C in this study. The etching rates of Si3N4 and SiO2 increased whereas the activation energies decreased with the addition of either HF or NH4F. As the concentration of HF is increased, the activation energies of Si3N4 and SiO2 etching further decreased. On the other hand, Si-containing additives increased the activation energy of SiO2 etching while the activation energy of Si3N4 etching was unchanged. In general, etching selectivity of Si3N4 to SiO2 decreased with the temperature of the etchant and the amount of change in the etching selectivity was different depending on the additives in H3PO4.