Reactive Ion Etching of Co–Zr–Nb Thin Film Using BCl3

Chlorine-based reactive ion etching (RIE) of a high-permeability Co–Zr–Nb film has been carried out. The etching rate was only about 10 nm/min in pure Cl2 in the temperature range in which anisotropic ion etching was dominant. Addition of BCl3 to the Cl2 resulted in an increase in the etching rate at low temperature. The activation energy in BCl3–Cl2 RIE was about 0.5 eV, whereas that in pure Cl2 RIE was 1.0 eV. The optimum BCl3 content was around 30 vol.%. The etching rate reached 750 nm/min at 1.2 W/cm2 RF power density and 300° C etching temperature. This improvement is due to the heavier mass and the higher ionization rate of BCl3 than those of Cl2. The ratio of the side etching rate to the depth-etching rate was about 30%, when the RF power density was 1.2 W/cm2 in BCl3–Cl2 RIE. The side etching was suppressed by both an increase in the RF power and addition of SiCl4 or SiCl4–O2 to the BCl3–Cl2. Anisotropy was promoted by both an increase in the ion energy and sidewall protection by Si or Si-oxide. An etching rate of 200 nm/min at 150° C and 2 W/cm2 RF power density in BCl3–Cl2–SiCl4 RIE has been achieved. The etching selectivity vs SiO2 was 20 and the side-etching rate was only 2% of the depth-etching rate.