Crystal Orientation and Surface Roughness of Bi Films Prepared in Ionized Cluster Beam Apparatus

We have studied the effects of deposition conditions and underlayers on the crystal orientation and surface roughness of Bi films deposited by the ionized cluster beam method as a means of reducing the noise of MnBi magneto-optical disks. Substrate temperature and applied voltage strongly affect the crystal orientation and the surface roughness of Bi films. The c-axis orientation and surface flatness drastically deteriorate at substrate temperatures above 100° C, and the degree of orientation/flatness decreases as the applied voltage is increased. Surface roughness of Bi films is inversely proportional to the degree of c-axis crystal orientation, indicating that the surface roughness is determined by the growth rate of Bi crystal planes. The c-axis orientation and the surface flatness can be improved by using low-wettability underlayers, since crystal reorientation of the Bi films easily occurs on such underlayers. We find that sputter etching of SiN underlayers can improve the surface flatness of Bi films at 20 nm thickness.