Effects of hydrogen on sputter-deposited boron carbide films

Sputter deposition of B4C films requires precise control over the microstructure and the nucleation and growth of nodular defects. Here, we study the properties of B4C films deposited with substrate holder temperatures of 250, 450, or 510 °C and different substrate tilt angles by direct-current magnetron sputtering in either pure Ar or a mixture of 4% H2 in Ar as the working gas. Results show that the addition of H2 reduces the impedance of the plasma discharge, resulting in larger discharge currents at constant power, which is attributed to a lower ionization potential of H2 than Ar. More importantly, films deposited with the H2 containing plasma exhibit lower oxygen impurity incorporation, a lower density of nodular defects, and suppressed columnar microstructure. These results demonstrate the effectiveness of such a plasma doping approach to improve the properties of B4C films.