Microstructure of hard and optically transparent HfO2 films prepared by high-power impulse magnetron sputtering with a pulsed oxygen flow control

THIN SOLID FILMS

卷:619

Article

Pi, Nai-Wen¹  Zhang, Minghui¹  Jiang, Jiechao¹  Belosludtsev, Alexandr^2,3  Vlcek, Jaroslav^2,3  Houska, Jiri^2,3  Meletis, Efstathios I.¹ 

[1] Univ Texas Arlington, Dept Mat Sci & Engn, Arlington, TX 76019 USA

[2] Univ West Bohemia, European Ctr Excellence, Dept Phys, Univ 8, Plzen 30614, Czech Republic

[3] Univ West Bohemia, European Ctr Excellence, NTIS, Univ 8, Plzen 30614, Czech Republic

关键词: HfO2 films;    Reactive HiPIMS;    High-resolution transmission electron microscopy;    Electron diffraction;    Dense nano-columnar structure;   

DOI  :  10.1016/j.tsf.2016.10.059

来源: Elsevier

【 摘 要 】

Reactive high-power impulse magnetron sputtering was used to deposit HfO2 films on Si substrates using a voltage pulse duration, t1, from 100 to 200 mu s and an deposition-averaged target power density, , from 7.2 to 54 Wcm(-2). The effects of these processing parameters on the microstructure and properties of the films were studied by atomic force microscopy, nano-indentation, X-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Four HfO2 films were prepared with (1) t(1) = 100 mu s, = 7.2 Wcm(-2) (T100S7), (2) t1 = 200 mu s, = 7.3 Wcm(-2) (T200S7), (3) t(1) = 200 mu s, = 18Wcm(-2) (T200S18) and (4) t(1) = 200 mu s, = 54Wcm(-2) (T200S54). All films were found to be composed of an interlayer next to the Si interface followed by a nano-columnar structure layer. The interlayer structure of the films was found to contain a population of lower density nanoscale regions. A reduction in in films T200S54, T200S18, T200S7 and T100S7 caused an increase in the interlayer thickness and a decrease in the width of the nano-columnar structures from similar to 46 nm to similar to 21 nm. This microstructural change was accompanied by a concomitant change of the grain boundary structure from tight and interlocking in films T200S54 and T200S18, to rough and thicker (similar to 1 nm) boundaries in films T200S7 and T100S7. Films prepared with larger t1 = 200 mu s have a monoclinic HfO2 structure and that with smaller t1 = 100 mu s exhibits a mixture of monoclinic and orthorhombic HfO2. A high hardness of 17.0-17.6 GPa was shown for films with a monoclinic HfO2 structure. The films exhibited a refractive index of 2.02-2.11 and an extinction coefficient between 0.1 x 10(-3) and 1 x 10(-3) (both at a wavelength of 550 nm). High refractive index was achieved for films T200S54 and T200S18 owing to the presence of a dense microstructure with sharp and interlocking grain boundaries. (C) 2016 Elsevier B.V. All rights reserved.

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