Copper thin films deposited using different ion acceleration strategies in HiPIMS

The growth of Cu thin films by low-energy ion-bombardment using bipolar and conventional HiPIMS pulse configurations to the target in combination with different biasing methods of the substrate were investigated. For bipolar HiPIMS with a substrate at floating potential, XRD measurements indicate minimal ion acceleration and change in the crystal growth when increasing the substrate holder potential to the same level as the applied positive voltage. In contrast, using bipolar HiPIMS with a substrate at ground potential results in a similar ion current profile as in conventional HiPIMS with a synchronized pulsed bias with the same delay and timing as the positive pulse. Furthermore, the trend in crystal growth is the same such that a significant increase in the (200) intensity is observed within an ion acceleration window, 125-175 V. Using conventional HiPIMS with a continuous DC bias also results in Cu films exhibiting significant (200) peaks, but the ion acceleration window is shifted to 175-225 V. The observed differences in the film growth could be explained not only by the energy of the ions but also by the type of ions (working gas vs metal ions) that are accelerated during either the positive pulse or substrate biasing.