Substrate heating effects on composition, structure and ferromagnetic resonance properties of CoFeB thin films

We investigate the ferromagnetic resonance and crystallinity properties of CoFeB thin films grown on Si (1 0 0), at substrate temperatures from 20 °C to 800 °C. The X-ray diffraction data show that the CoFeB films are amorphous when deposited at a substrate deposition temperature of less than 500 °C. X-ray diffraction peak analysis matched the crystalline peaks of films grown at 500 °C to a face-centered cubic (1 1 0) Co₇Fe₃ phase. Increasing the substrate deposition temperatures increased above 600 °C leads to the formation of a face-centered cubic silicide FeCo₂Si (2 2 0) and oxide Fe₂CoO₄ (4 0 0). Upon crystallization into different phases at a substrate deposition temperature above 500 °C, the soft ferromagnetic properties of CoFeB are lost. The coercivity of the deposited thin films increases from 20 Oe at room temperature to a maximum of 275 Oe at 700 °C. The peak-to-peak ferromagnetic resonance linewidth at 15 GHz, increases from 80 Oe at room temperature to 790 Oe at 500 °C. The grain size of the as-deposited samples increases with substrate temperature from 20-nm at room temperature to 241-nm at 800 °C as determined by atomic force microscopy.