Investigation of etching properties of metal nitride/high-k gate stacks using inductively coupled plasma

Abstract

Etching properties of metal nitrides (TaN, TiN, and HfN)/high dielectric constant material (HfO2) gate stacks in Cl2 and HBr were investigated using inductively coupled plasma. The linear dependence of etch rates on the square root of bias voltage indicates the dominance of ion-induced etch mechanism of the metal nitrides. This phenomenon is well explained by internal binding energy of substrate, evaporation temperature, and Gibb’s free energy (ΔGf°) of formation of byproducts. The addition of O2 in Cl2 and HBr decreased etch rates of the metal nitrides and HfO2; however, for O2 concentration lower than 1.5% in Cl2, a slight increase in etch rates of the metal nitrides was observed. X-ray photoelectron spectroscopy revealed that residues remain more on the sidewalls of gate stacks than the bottom of spaces between gates. The addition of O2 and the use of a SiO2 mask to increase etch selectivity of metal nitrides with respect to high-k dielectric increased surface roughness and formed micromasks on the etched surface. The optical emission signals from N, Cl, and Ta–Cl byproducts were sensitive enough to control the etch endpoints of the TaN∕HfO2 stack structures.