Effects of substrate bias voltage on projection growth in chromium nitride films deposited by arc ion plating

Projection growth in chromium nitride films deposited by arc ion plating was studied as a function of substrate bias voltage by scanning electron microscope and stylus instrument. Most of projections were observed as the tops of tapered crystallite developed on droplets. Most of the droplets were implanted under the projections, although there existed some droplets on film surface. And growth morphology of projections on droplets was strongly affected by substrate bias voltage. Under the condition of low substrate bias voltage, projections grew larger than droplets to roughen the film surface. On the other hand, under the condition of high bias voltage, diameters of projections were smaller than the droplets to be embedded to flatten the surface as film deposition progresses further. Then, the number and size of projections on film surfaces and surface roughness of the film decreased with an increase in substrate bias voltage. Besides, droplets adhering on film surface shadowed the underlying film from further deposition of chromium nitride, resulting in the appearance of toroidal shaped voids along the droplets. Though these toroidal shaped voids developed upward from the shaded bottom surface along the droplets at low bias voltage, these voids became smaller to be detected just beneath the droplet at the higher bias voltage. These results imply that the resputtering effect on geometrical projections, strengthened by the increase in substrate bias voltage, as generally accepted, would cause the decrease of the deposition rate on projections much more than on the flat surface of the film, and resputtered materials would also fill the space between the droplets and the film surface, resulting in the embedment of projections as film deposition progresses.