Limitations to copper grain growth in narrow trenches

Even though large variations are seen in transformation times for Copper blanket layers when changing layer thickness or plating current, the activation energy for secondary grain growth is always /spl sim/ 0.9 eV. The difference is attributed to variations in the number of 'nucleation sites' for secondary grains. As the number of such sites is extremely low in trenches, transformation times are very high even at elevated temperatures.