Effect of structure on the mechanical properties of Ta and Ta(N) thin films prepared by reactive DC magnetron sputtering

In this study, the effects of N content, grain size, and growth texture on the hardness and Young's modulus of nanocrystalline Ta and Ta(N) thin films deposited using reactive DC magnetron sputtering are examined. The structure of the films was determined by X-ray diffraction and the hardness and modulus by nanoindentation, Pure Ta films typically exhibit a dominant (200) growth mode of the beta-tetragonal phase. However, under certain conditions significant (202) growth is noted which is correlated with a marked decrease in hardness (from 18 to 11 GPa). Addition of N (pN(2) = 0.026, 0.052, and 0.100 mTorr) increases the hardness of the Ta films with the maximum hardness (32 GPa) obtained for the films with pN(2) = 0.100 mTorr. In the case of low Ta(N) films (pN(2) = 0.026 mTorr), the hardness exhibits a clear microstructural dependence. A decrease in the grain size causes the hardness to increase from 16 to 24 GPa. The Young's modulus values, however, do not exhibit any systematic variation with either growth texture or grain size.