Nitrogen incorporation and composition facilitated tailoring of the optical constants and dispersion energy parameters of tungsten oxynitride films

JOURNAL OF ALLOYS AND COMPOUNDS

卷:683

Article

Nunez, O. R.¹  Tarango, A. J. Moreno¹  Murphy, N. R.²  Ramana, C. V.¹ 

[1] Univ Texas El Paso, Dept Mech Engn, El Paso, TX 79968 USA

[2] Mat & Mfg Directorate RX, 3005 Hobson Way, Dayton, OH 45433 USA

关键词: Tungsten oxynitride;    Thin films;    Optical constants;    Ellipsometry;   

DOI  :  10.1016/j.jallcom.2016.04.182

来源: Elsevier

【 摘 要 】

Optical properties, including the index of refraction, extinction coefficient and band gap of 100 nm thick tungsten oxynitride (W-O-N) films are reported. In addition, the Wemple and DiDomenico (WDD) model was used to calculate the dispersion energies and oscillator energies of the films, establishing a correlation among the films' optical, chemical, and physical properties, as a function of nitrogen content. Nitrogen concentration in the W-O-N films was varied by adjusting the nitrogen gas flow rate from 0 to 20 sccm while keeping total gas flow (nitrogen _ oxygen _ argon) constant at 40 sccm. Both the index of refraction (n) and extinction coefficient (k) of W-O-N films demonstrated a high degree of sensitivity to the nitrogen content during deposition. The optical constants of films fabricated without any nitrogen correspond to transparent W-oxide (WO3) where n(550) = 2.1 and k(550) = 0.0. The magnitude of the spectral response for both n and k tends to increase with increasing nitrogen content. Systematic increases of the films' nitrogen content lead to the formation of W-oxide (E-g approximate to 3 eV) -> W-O-N oxynitride semiconductor (E-g approximate to 2 eV) -> N-rich W-O-N semi-metal (E-g < 2 eV) -> WN2 type metallic transition was evident in dispersion profiles of n and k for W-O-N films with increasing nitrogen content. The corresponding mechanical characteristics, namely hardness (H) and Young's modulus (E), attain a maximum of 4.46 GPa and 98.5 GPa, respectively, at a nitrogen flow rate of 5 sccm, at which point H and E values decrease to attain 3.57 GPa and 72.91 GPa, respectively. The trend observed in H and E values correlate with theW-O andW-N bonds formation inW-O-N along with the interruption of local epitaxy attributed to increasing nitrogen content within the growth chamber. A correlation among the nitrogen content, optical constants and physical properties, along with the associated dispersion model, is presented to account for the optical properties of sputter-deposited W-O-N films. The results demonstrate that tailoring the properties of W-O-N films for desired applications can be achieved by tuning the nitrogen content and chemical composition. (C) 2016 Published by Elsevier B. V.

【 授权许可】

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