Structures and Mechanical Properties of Cu-W Thin Films Deposited by Mosaic Target Magnetron Sputtering
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 micro-scope(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 in-dentation 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.
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