Effect of grain orientations of Cu seed layers on the growth of <111>-oriented nanotwinned Cu

We investigate the growth of Cu films on two different Cu seed layers: one with regular < 111 >-oriented grains and the other with very strong < 111 >-preferred orientation. It is found that densely-packed nanotwinned Cu (nt-Cu) can be grown by pulsed electroplating on the strong < 111 >-oriented Cu seed layer without a randomly-oriented transition layer between the nt-Cu and the Cu seed layer. The electroplated nt-Cu grow almost epitaxially on the seed layer and formed < 111 >-oriented columnar structures. However, with the regular < 111 >-oriented Cu seed, there is a randomly-oriented transition layer between the nt-Cu and the regular < 111 >-oriented Cu seed. The results indicate that the seed layer plays a crucial role on the regularity of < 111 >-oriented nanotwinned Cu.