Effect of thermal stress on anisotropic grain growth in nano-twinned and un-twinned copper films

Oriented and nanotwinned copper (nt-Cu) of 3.8 µm thickness was electroplated on a Si wafer substrate for thermal stress measurement from room temperature to 400 °C by bending beam method. Microstructure transformation in the copper thin film was studied after the thermal process. At 150 °C, the maximum compressive stress reached 150 MPa, and the (111) oriented nanotwinned copper began to transform to (200) orientation. Beyond 150 °C, anisotropic grain growth of (200) grains is faster. For comparison with the random-oriented copper thin films without nanotwins, we discover that the nanotwinned films can withstand a compressive stress of 1.5 times greater than the random copper thin films. This large thermal stress provides the driving force for anisotropic grain growth in the oriented nano-twin Cu, which can reach several hundred µm.