Influence of O2 flow rate on the structural properties of MgO films deposited by dual magnetron sputtering

MgO films were deposited by a mid frequency dual magnetron reactive sputtering system composed of two identical magnetrons and powered by a sinusoidal generator. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, and a diode discharge device were used to characterize surface morphology, crystalline structure, and secondary electron emission (γ) coefficient of the films, respectively. The influence of O2 flow rate with a constant Ar flow rate of 120 sccm on the structure and properties of the films was systematically studied. As the O2 flow rate is increased from 5 to 14 sccm, the intensity ratio of the (111) to (200) peak of cubic MgO phase increases significantly, leading to a change of the film texture from a combined (100) and (111) preferred orientation to a highly (111) preferred orientation. The (111) peak center shifts to a larger angle, and the full width at half maximum of the (111) peak decreases greatly, indicating a considerable decrease of defect density in the films. The increases in the relative intensity of the (111) peak and the decrease in the defect density in the films contribute to a remarkable increase in the γ coefficient of the films. Furthermore increase of O2 flow rate results in no significant change in the crystalline structures and the γ coefficient of the MgO films.