Anisotropic etching of CoFeB magnetic thin films in C2H5OH/Ar plasma

The etch characteristics of TiN hard mask-patterned CoFeB thin films were investigated by inductively coupled plasma reactive ion etching in an C2H5OH/Ar gas mixture. The effects of gas mixture concentration, rf coil power, dc bias voltage, and process pressure on the etch profile were investigated. Etch profiles with a high degree of anisotropy were achieved with C2H5OH concentrations from 25% to 50%. Further increases in the C2H5OH concentration decreased the degree of anisotropy of the etch profile. The etch profile improved as the rf coil power and dc bias increased and the process pressure decreased. Optical emission spectroscopy revealed the presence of [C], [H], [O], and [Ar] species, among others, in the plasma, while X-ray photoelectron spectroscopy analysis of the CoFeB thin film surface revealed the presence of Co, Fe, and B oxides, and the deposition of carbon-containing compounds. Results suggest that the etch mechanism is driven by physical sputtering, assisted by oxidation of the films and formation of a CxHy inhibition layer.