Microstructure and optical properties of MgO films synthesized by closed-field unbalanced magnetron sputtering with additional electron emission

This paper investigated the discharge behaviour, microstructure and optical properties of magnesium oxide (MgO) films synthesized by closed-field unbalanced magnetron sputtering (CFUBM) with additional electron emission. For the evaluation of the effects on closed-field magnetic configuration and additional electron emission, MgO films were deposited by three types of magnetron sputtering with a circular Mg target and various O2 partial pressure: (i) the single unbalanced magnetron sputtering (UBM), (ii) CFUBM by a symmetrical arrangement of four magnetrons and (iii) CFUBM with additional electron emission by W-filament. As magnetic closed-field and additional electron emission were employed to magnetron discharges, poisoning ratio was reduced and deposition rate was increased approximately 1.5 times in comparison with that obtained in the single UBM. The saturated ion current density and the substrate temperature were increased with the attachment of magnetic closed-field and additional electron emission in MgO discharges, which means that these played an important role to enhance plasma density and ionization rate. As a results of microstructure and optical property analyses, an employment of magnetic closed-field and additional electron emission led to the high density MgO films with higher refractive index and transmittance, although MgO film coated by CFUBM showed the lowest refractive index due to the large number of planar defects.