Line Scaling Effect On Grain Structure For Cu Interconnects
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The effect of line scaling on Cu grain structures has been investigated by using both plan-view and cross-sectional transmission electron microscopy (TEM) techniques. Cu damascene lines with three different line widths of 850, 185 and 60 nm were studied. The plan-view TEM images revealed that the 850 nm lines had both polycrystalline and bamboo-like grain structures, whereas the 185 and the 60 nm lines had near bamboo-like structures. Statistical analysis was performed on the grain size distributions for both 185 nm and 60 nm lines. The results showed that the 185 nm lines followed a normal grain growth behavior, while the 60 nm lines deviated from normal grain growth with excessive small grains at the lower percentile which was attributed to scaling-induced small grain growth. Further analysis by cross-sectional TEM along the Cu trench line direction revealed that the 850 nm lines had bamboo-like structures across the thickness while the 185 nm and the 60 nm lines showed a combination of bamboo-like and multigrain structures with small grain clusters concentrated at the trench bottom.