Tuning Stress in Cu Thin Films by Developing Highly (111)-Oriented Nanotwinned Structure

We have examined the effect of different bath temperatures on residual stress of both the random-oriented Cu films and the highly (111)-oriented nanotwinned Cu films by synchrotron radiation x-ray measurements. The bath temperature varied from 15°C to 40°C. The results indicate that the average residual stress in the highly (111)-oriented nanotwinned films is higher than that in the randomly oriented Cu films. However, the stress in the highly (111)-oriented Cu decreases with increasing bath temperature. The average residual stress can be reduced from 253 MPa electroplated at 15°C to 95 MPa under a bath temperature of 35°C. We could successfully tune and measure residual stress of the Cu thin films. The films with low residual stress prevent warpage from occurring on the substrate and lower the processing failure in copper direct bonding and other processes that need alignment.