The formation and characterization of rare earth boride films

Thin films of several rare earth borides were prepared by either dual-electron-beam evaporation (YB2, YB4 and YB6) or sputtering from a boride target (LaB6). Although values for bulk resistivities and work functions for rare earth borides are low (e.g.ϱ = 17 μΩ cm and o = 2.66 eV for LaB6) thin films of rare earth borides show significantly higher resistivities and work functions (ϱ = 96 μΩ cm and o = 3.8 eV for LaB6 films). Large resistivity increases were observed for rare earth boride films subjected to a 30 min steam oxidation at 1000°C. Adding silicon to the boride films allowed the film to remain conductive even after a 30 min, 1000°C steam oxidation. Also, silicon additions to LaB6 films resulted in a reduction in the film stress after a 1000°C anneal. The stresses within LaB6 and YB2 films were found to be tensile after a 30 min, 1000°C nitrogen anneal (σYB2 = 1.3 x 109 N m-2; σLaB6 = 8 x 108 N m-2). LaB6 films are shown to behave as semi-infinite diffusion sources for boron.