Impact of annealing, surface/strain energy and linewidth to line spacing ratio on texture evolution in damascene Cu interconnects

Texture variation has been investigated as a function of linewidth in damascene copper interconnect lines and Cu blanket film. Two set of specimens, one in as-deposited and the other one in annealed condition, with 10 different linewidths and line spacings were examined using orientation imaging microscopy (OIM) and X-ray diffraction (XRD). XRD results demonstrated the presence of (111) fiber texture in most of the specimens together with some contribution from (111)<110> texture in the narrowest lines. There was an increased tendency of the (111) planes to align <112> direction along the trench length with increasing linewidth. Texture was sharper in the narrower as-deposited lines but became random upon annealing due to increased twinning. Multiple twinning also led to the weakening of (111) texture in the Cu blanket film. There was an increase of (100) texture upon annealing in the narrower lines. The formation of (100) texture and persistence of (111) texture upon annealing indicates the competition between the strain and surface/interface energy in the narrower linewidths. The average area fraction of (111), (110) and (100) fiber texture components computed using electron backscatter diffraction (EBSD) and XRD data, within 10° to 15°, showed an increase of (110) texture in the narrower lines upon annealing. It seems that (110) texture is being preferred to reduce the total energy of the system amidst the competition between the interface and strain energy. The role of linewidth to line spacing ratio on influencing the texture strength was identified. EBSD investigations found significant texture variations in the local grain population of the interconnects.