Structures and Mechanical Properties of Cu-W Thin Films Deposited by Mosaic Target Magnetron Sputtering

Abstract

In order to study the effects of W content on the structure and mechanical properties of Cu-W thin films, these films were prepared by magnetron sputtering process using mosaic combination targets. The composition, structure and surface morphology of the thin films were characterized, respectively, by energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), high-resolution transmission electron microscope(HRTEM), scanning electron microscope(SEM) and atomic force microscope(AFM). The yield strength(σ0.2), critical strain for crack initiation(εc), elastic modulus(E) and microhardness(H) of the thin films were tested using micro-force testing system and nano indentation instrument, respectively. Results showed that the composition of the thin films could be controlled by adjusting the proportion of the W target area. When the proportion of the W target area was increased from 5% to 25%, the W content in the Cu-W thin films was observed to gradually increase from 2.30%(atomic fraction, the same below) to 15.10%, accompanied by the formation of an fcc Cu(W) metastable quasi-solid solution. As the W content increased, the average grain size of the Cu-W thin films was seen to gradually decrease from 28 nm to 18 nm, the quasi-solid solubility was noted to gradually increase from 1.30%W to 9.50%W, and an improvement in the surface smoothness of the thin films was recorded. With the increase of W content, it was found that the yield strength(σ0.2) and microhardness(H) of the Cu-W thin films increased significantly, the elastic modulus exhibited a slight increase, while the critical strain for crack initiation(εc) experienced a decrease. The Cu-15.10% W thin film was determined to possess the smallest average grain size and the highest surface smoothness, along with the highest yield strength, hardness and elastic modulus(σ0.2 = 0.86 GPa, H = 6.1 GPa, E = 123.5 GPa); the critical strain for crack initiation(εc) value was 0.84%, indicating the best comprehensive mechanical performance.

Keywords

• magnetron sputtering; cu-w thin films; structures; mechanical properties