Effect of deposition conditions on mechanical stresses and microstructure of sputter-deposited molybdenum and reactively sputter-deposited molybdenum nitride films

Abstract

A combined investigation of mechanical stress generation by in situ substrate curvature measurements during the growth of MoN x thin films, with 0≤x≤0.35, and of structural properties by ex situ X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission electron diffraction (TED), X-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS) is reported. It was found that the Mo film stresses strongly depended on the Ar sputtering pressure and changed from highly compressive to highly tensile in a relatively narrow pressure range of 6–12 mTorr. For pressures exceeding ∼40 mTorr, the stress in the film was nearly zero. Cross-sectional TEM measurements indicated that the compressively stressed films contained a dense microstructure without any columns, while the films having tensile stress had a very columnar microstructure. High sputtering-gas pressure conditions yielded dendritic-like film growth, resulting in complete relaxation of the mechanical tensile stresses. It was also found that the properties of the deposited MoN x films depended not only on the nitrogen partial pressure in Ar–N 2 gas mixtures but also on the total sputtering-gas pressure. Cross-sectional TEM studies showed that an average column width for 160 nm-thick films near stoichiometry of Mo 2N was about ∼15–20 nm. Using the electron scattering data collected from a range of crystalline samples for calculating the pair distribution function (PDF) by Fourier transformation in real space, MoN and MoMo bonding in the films was also identified. Once the Mo 2N phase was formed, the density, microstructure and bonding feature were similar and insensitive to the total sputtering pressure used in this study.