Origin of residual stress and its relationship with crystallographic orientation of sputtered thin films

Abstract

$Y_2O_3$ thin films were deposited by reactive sputtering of an Y target in Ar and $O_2$ gas mixture. Intrinsic stresses and the Ar content in the films were measured by the sines quare psi method of x-ray diffraction and wavelength dispersive spectrometer, respectively. At low working pressures the films had high compressive stresses. As working pressure increased, compressive stress was relaxed. Ar content was high in the film that had high compressive stress. After annealing of the films at 700℃, the compressive stress was largely relaxed but Ar content remained unchanged. These results clearly showed that compressive stress in $Y_2O_3$ films was not caused by Ar entrapment as an impurity but by Ar bombardment. Intrinsic stress was almost independent of the $O_2$/Ar flow ratio, showing that O bombardment was equal to Ar bombardment in affecting the intrinsic stress in $Y_2O_3$ films. The independence of intrinsic stress of $O_2$/Ar flow ratio was explained by the concept of $M_i\frac^{1}{2} θ ±(M_t^2 - M_i^2 sin ^2 θ)^\frac{1}{2}]$/(M_i + M_t) instead of the Mt/Mi ratio, where $M_t$ is the atomic mass of the target material, $M_i$ is the atomic mass of the sputtering gas, and θ is the scattering angle. Cu thin films were deposited by bias sputtering and the film density was measured by grazing incidence x-ray reflectivity. The influence of the experimentally measured film density on residual stress, which previously few studies reported about, was investigated. Without bias voltage, the relative film density was low and the tensile stress was high. With increasing bias voltage, tensile stress decreased and saturated to nearly zero at a bias voltage of -100 V while the film density increased and saturated to nearly bulk value at a bias voltage of -100 V. These results were consistent with those from previously reported molecular dynamic simulations. From the consideration of the Morse potential for relatively dense films, it was possible that tensile stress d...