Impurity-controlled film growth and elastic properties of CoCrCuFeNi thin films

Abstract

The growth mode during physical vapor deposition of metallic thin films is very sensitive to the presence of impurity species. These impurities can originate from the residual ambient gases present in the vacuum chamber and usually impede continued crystal growth by inducing renucleation. During magnetron sputtering at intermediary base pressures (~10−4Pa), the effect of these impurities can be estimated from the ratio of the impurity flux to the metallic flux. In this study, the influence of the ambient impurity flux on the growth mode of CoCrCuFeNi High-Entropy Alloy (HEA) thin films is investigated. It is shown that the impurity-to-metal flux ratio effectively controls the texture, grain size, porosity, and elastic properties of the nanocrystalline CoCrCuFeNi thin films. A less clear (111) fiber texture is observed at higher impurity-to-metal flux ratio. With increasing impurity-to-metal flux ratio the grain size decreases while the porosity increases. The elastic constants, and Young's modulus for CoCrCuFeNi is reported to be the highest for the 〈111〉 direction. Hence, the change in film texture also affects the elastic constants and Young's modulus which tend to become lower as more grains with different orientation are observed at higher flux ratios. This study demonstrates that an exact knowledge of the impurity-to-metal flux ratio, or otherwise stated, of the base pressure and deposition rate during sputter deposition is imperative for the synthesis of HEA films with reproducible properties.