Influence of liner-system and Cu-layer thickness on the grain structure of electroplated Cu

The grain structure of 1.2 μm electroplated Cu layers with undoped Cu seed layer has been investigated using electron backscatter diffraction (EBSD). Therefore orientation imaging microscopy (OIM) was carried out on samples with five different liner systems (Ti, Ta, WTi, TiN and TaN), three different annealing steps (self-anneal at room temperature, 1 h at 110 °C and 0.5 h at 380 °C) and two plating chemistries with varying acid content. In addition, samples with 1 μm and 3 μm electroplated Cu on an Al-doped Cu seed layer have been analyzed in order to investigate the influence of the plated layer thickness on grain structure. The results show that the grain structure is dominated by low energy CSL boundaries, especially Σ3 twins, which can be found in almost every grain. This twinning causes a typical deviation from the expected {111} orientation parallel to the sample surface towards {115} orientations. This is the result of the self-annealing process (caused by recrystallization). Differences in orientation caused by the liner system will be shown as well as influences of the Cu-plating thickness on the fraction of {101} orientations. Finally, changes in grain size and twinning fraction due to subsequent annealing steps will be presented.