Structure of MgO Films Prepared by Ion Beam Sputtering

Abstract

Preferred orientation and microstructure of MgO films prepared by ion beam sputtering were investigated. The crystallographic orientation of MgO films was a function of the substrate angle (δ), O2 gas partial pressure (PO2) and the substrate temperature (Ts). As δ changed from 90° to 0°, the transmission electron diffraction (TED) pattern of the films deposited in PO2 of 1×10-4 Torr at Ts=R. T. changed from a random orientation to the (111) preferred orientation in which the crystallographic (111) plane was parallel to the substrate surface. An increase in PO2 from 0.1×10-4 to 10×10-4 Torr caused the (111) preferred orientation. At Ts>100°C, the TED pattern of the films on NaCl (200) deposited with δ=90° showed epitaxial growth in contrast with a random orientation at Ts<100°C. Annealing below 500°C did not change the orientation and size of the crystallite. Annealing above 1000°C for 30min, however, caused crystallite growth from 5nm to 20nm without any change in orientation. This size is still smaller than that of the crystallites deposited on a heated substrate. The origin of the crystallographic preferred orientation of the MgO thin film deposited by ion beam sputtering was explained in terms of the growth competition. The (111) preferred orientation becomes predominant in the growth competition over others with decreasing the arrival ratio of Mg/O.