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. etching rate was only about 10 nm/min in pure Cl-2 in the temperature range in which anisotropic ion etching was dominant. Addition of BCl3 to the Cl-2 resulted in an increase in the etching rate at low temperature. The activation energy in BCl3-Cl-2 RIE was about 0.5eV, whereas that in pure Cl-2 RIE was l.OeV. The optimum BCl3 content was around 30 vol.%. The etching rate reached 750 nm/min at 1.2 W/cm(2) RF power density and 300 degrees C etching temperature. This improvement is due to the heavier mass and the higher ionization rate of BCl3 than those of Cl-2. The ratio of the side etching rate to the depth-etching rate was about 30%, when the RF power density was 1.2 W/cm(2) in BCl3-Cl-2 RIE. The side etching was suppressed by both an increase in the RF power and addition of SiCl4 or SiCl4-O-2 to the BCl3-Cl-2. 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 degrees C and 2 W/cm(2) RF power density in BCl3-Cl-2-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.