Microstructure and Texture of Ultra-High Purity Copper under Changed Rolling Strain Paths and Subsequent Recrystallization Annealing

For advanced integrated circuits semiconductor chip, the uniformity of microstructure and texture is increasingly required for copper target material of ultra-high purity (≥99.9999%). To this end, well-customized rolling and annealing routes for the raw material of Cu are highly needed. In the study, unidirectional rolling (UR) and cross rolling (CR) were utilized in processing the supplied Cu, both with 50, 70, and 90% thickness reduction, respectively. The rolled samples then underwent identical annealing at 300°C for 60 min. The rolled and recrystallized microstructure and texture were characterized by electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Results showed that the CR samples exhibited severer grain fragmentation, more homogeneous microstructure and weaker texture than the UR samples, especially for the samples of 90% thickness reduction. Moreover, dynamically recrystallized grains were observed in both UR and CR samples with 90% thickness reduction due to the raised temperature during severe plastic deformation. Thanks to the more uniform deformation, the annealed CR samples enjoyed finer grains of more random textures than the annealed UR ones. Therefore, cross rolling is preferable for imparting Cu sputtering targets with the required uniformity.