Preparation and characteristics of nickel oxide thin film by controlled growth with sequential surface chemical reactions

Abstract

Nickel oxide films have been fabricated by various physical and chemical vapour deposition (CVD) techniques such as reactive sputtering [1] and plasma-enhanced chemical vapour deposition [2] because their chemical stability as well as their optical and electrical properties are excellent. If the fabrication technology could lead to growth on an atomic scale, it would be rauch more interesting also for applications to soft X-ray multilayers and neutron optics because compound multilayer structures consisting of NiXx (X = C, N, dry air) layers have been the focus of recent attention [3]. In recent years, atomic layer deposition of A1203 [4-7], TiO2 [8, 9] and multilayers based on A1203/TiO2 [10] by sequential surface chemical reactions has been reported. This deposition technique could be used to sequentially dose a surface with appropriate chemical precursors to promote surface chemical reactions that are inherently self-limiting. The selflimiting nature of the surface reactions enables precise control of the thickness of the deposited layers on an atomic scale and gives rise to homogeneous films on large areas. In this work, bis-methylcyclopentadienyl nickel (Ni(CH3CsH4)2) and hydrogen peroxide (H202) were used for controlled growth of amorphous nickel oxide films by sequential surface chemical reactions, because amorphous structures are suitable for applications to soft X-ray multilayers due to their smooth surface and interface. The experimental setup comprised a stainless steel vacuum chamber with computer-controlled leak and gare valves, a capacitor manometer and a substrate holder connected to a heater. The substrate was cut from a (100)-orientated Si wafer. As vapour sources, high purity bis-methylcyclopentadienyl nickel (Ni(CH3C»H4)2; Trichemical Laboratory Inc.) and H 2 0 2 w e r e used. As shown in Fig. 1, the vapour pressure of Ni(CH3CsH4)2 is high among those of nickel compounds [11], which makes it rather easy to u s e . H 2 0 2 w a s prepared by vacuum distilling