Electroplated Cu films undergo a remarkable recrystallization at room temperature that has been associated with dislocations and defects arising from the influence of surface-active additives during plating. In the process of plating, the composition of the bath changes as the organic additives are depleted by incorporation into the Cu films or electrolytic decomposition and replenished by fresh additions. Given the sensitivity of the plating process to low concentrations of additives, the properties of the plated Cu might be expected to differ between a freshly prepared bath and an older bath that has processed thousands of wafers and achieved a steady state composition of additives and by-products.
In this paper we compare the recrystallization rates of Cu films deposited from two such baths on wafers with damascene trenches of widths from 0.3 to 5 μm. Films deposited from the older bath consistently recrystallize at a faster rate for all trench widths and both barrier materials (Ta, TaN) studied. The concentration of impurities is comparable in the two films. Therefore, the difference in rates is likely due to a difference in defect densities in the film due to different adsorbate/surface interactions during plating. Although the recrystallization rates vary, X-ray diffraction pole figure analysis of films plated from the two baths show no differences in texture. Sidewall growth components are visible in both sets of samples. Data on the influence of the barrier material and trench width on recrystallization rates are also presented.