Structure and thermal stability of amorphous Co23Fe60B17 film on Si substrate

Abstract

Structural evolution with thermal annealing of the thin film of amorphous Co23Fe60B17 depositors on Si/SiO2 substrate has been studied using grazing incidence x-ray diffraction, soft x-ray absorption spectroscopy (SXAS), and secondary ion mass spectrometry (SIMS). Amorphous to crystalline transformation starts occurring in the film at a temperature between 200 and 300 °C, which is significantly below the crystallization temperature of amorphous ribbon of similar composition. In the process, the body centered cubic CoFe is the primary phase to precipitate out. Combined SIMS and SXAS measurements show that at the surface iron gets preferentially oxidized as compared to cobalt. Surface oxidation is found to decreases with thermal annealing in vacuum. Boron is found to gradually migrate to the surface and get sublimated. Higher surface and interface energies and depletion of B with thermal annealing are expected to be the cause of lower thermal stability of the film. Magneto-optical Kerr effect measurements show that the as-deposited film possesses a well-defined uniaxial magnetic anisotropy. The anisotropy does not disappear even after the partial crystallization of the film. This suggests that the origin of the observed anisotropy is a combined effect of long-range internal stresses and possible chemical short range order in the film.