Toshio Haba

Aspect Ratio Dependence of the Resistivity of Fine Line Cu Interconnects

The effect of aspect-ratios of very narrow Cu interconnects of less than 100 nm on the resistivity has been discussed. From longitudinal cross-sectional transmission electron microscope (TEM) observation, many very small grains were observed at the bottom of the trench, while larger grain sizes are predominant in the upper part of the Cu interconnects. The resistivity was found to decrease significantly when increasing the aspect-ratio in fine line Cu wires due to the larger grain size distributions in the upper part of the Cu interconnects with higher aspect-ratios. This result demonstrates that the aspect-ratio of Cu wires are effective for controlling the resistivity in future Cu interconnects with very narrow and shallow dimensions.

Advanced trench filling process by selective copper electrodeposition for ultra fine printed wiring board fabrication

A trench filling type process to fabricate ultra-fine pitch printed wiring boards was developed by combining nano-imprint lithography (NIL) and selective copper deposition. Copper was electorodeposited selectively inside the trenches fabricated in the dielectric layer by NIL process, without causing excess deposition on the surface. The selective deposition was realized by a novel electrodeposition bath employing Cyanine dye as an inhibiting additive. The recessed interconnections with 10 µm line and space dimension were successfully fabricated. The developed process shows significant advantages to the processes employing non- or less- selective deposition, which require planarization to remove excess copper deposited on the surface, and may potentially replace the state of the art semiadditive process.

Filling 80-nm-Wide and High-Aspect-Ratio Trench with Pulse Wave Copper Electroplating and Observation of the Microstructure

To completely fill 80-nm-wide trenches with high-aspect-ratio (>6) Cu electroplating, we investigated the influence of pulse wave electroplating conditions. Peak current density and current-off time during pulse wave plating were found to affect bottom-up filling. Bottom-up filling was confirmed to occur when peak current density, current-on time and current-off time were 100 mA/cm2, 3 and 300 ms, respectively. The microstructure of the trench was observed before and after annealing at 673 K by transmission electron microscope. After annealing, the grain size increases and grains cross the trench width. The size of grains formed by pulse wave plating before and after annealing were 37.5 and 96 nm, respectively. These values were similar to those for DC plating. Pulse wave electroplating is, therefore, promising as a step in the dual damascene process for fabricating very narrow high-aspect-ratio Cu wiring.