Barrier layer, geometry and alloying effects on the microstructure and texture of electroplated copper thin films and damascene lines

The effect of two different barrier materials (sputtered Ta and TaN) and their layering schemes on the microstructure of the sputtered copper seed and electroplated Cu films and interconnects was investigated using electron backscatter diffraction and X-ray diffraction. The films had a predominantly (111) texture and the microstructural change with the change of barrier layer material was minimal. The sidewall constraint effect on the microstructure development in narrow damascene trenches on Ta barrier was also examined by analyzing 0.5 μm deep lines over a range of different line widths (0.2-5.0 μm). The constraint due to the sidewall produces an [011] orientation along the line length. The in-plane texture strengthens with decreasing line width. The crystallographic texture was a function of line width with the intermediate line widths (near 1 μm) having the weakest texture and highest fraction of twin boundaries compared to the other line widths. The effect of alloying on the microstructure and texture was examined in similar damascene lines with a Cu-1% Ag seed layer before electroplating with pure Cu. The Ag addition decreased the average grain size without affecting the texture.