Interface study on the effect of oxygen/nitrogen ratio in Ni/Ti multilayer deposited by reactive sputtering

Abstract

Since the growth morphology along and perpendicular to the interface is important for supermirror applications, the dependence of this on the reactive gas has been investigated in Ni/Ti multilayers prepared by reactive magnetron sputtering with variable O _2 /N _2 ratios. The interface properties are characterized by GIXRR, XDS, and TEM measurements. Compared to the case without O _2 , the presence of 20% O _2 in the deposition of Ni layers contributes to smooth and abrupt interfaces. It also suppresses the accumulation of interfacial roughness with the increasing number of layers. However, the abundant oxygen content results in a striking degradation of interface quality associated with the crystallization evolution. Moreover, the lateral correlation length of interfacial roughness exhibits a consistent tendency with the grain size as the oxygen content increases. Following the XPS depth profiles, although N _2 and O _2 gases were applied in the Ni layer deposition, the N and O were only detected in the Ti layers as the compound for the high chemical activity of Ti. The elemental form in the Ni layers corresponds to the crystalline structure inferred by XRD measurements.

Keywords

• interface
• crystallization
• composition
• reactive sputtering
• Ni/Ti multilayer