Takahiro Nagano

Observation of microstructures in the longitudinal direction of very narrow Cu interconnects

We have succeeded in observing the longitudinal microstructure of very narrow Cu interconnects for the first time. We found that the average grain sizes along the longitudinal direction of Cu interconnect trenches increased with increasing line width, and they were 278 nm for 80 nm, 303 nm for 100 nm, and 346 nm for 180 nm wide interconnects. Ratios of the average grain size to line width were 3.5 for 80 nm, 3.03 for 100 nm, and 1.9 for 180 nm line widths.

The Development of an Innovative Process of Large Grained and Low Resistivity Cu Wires for less than hp 45nm ULSI

We have developed an innovative process to create large grained and low resistivity Cu wires for less than hp 45 nm ULSIs. The resistivity of the 50 nm wide Cu wires by an innovative high purity process is found to be 21% lower than those created by the conventional process. It was also found that Cu wires formed with the new high purity process have larger grains with a smaller spread and a lower impurity concentration than those made with the conventional process. This innovative new process is expected to be a powerful candidate for created Cu wire of less than hp 45 nm ULSIs.

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.

Characteristics of 4H-SiC n- and p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors with Ion-Implanted Buried Channel

We investigated the electrical characteristics of 4H-SiC n- and p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) with ion-implanted buried channels. The effects of the impurity concentrations of the buried channel (Cbc) on their electrical characteristics were quite different. In the case of n-channel MOSFETs, the threshold voltage decreased and the channel mobility increased with an increase in Cbc. On the other hand, in the case of p-channel MOSFETs, the threshold voltage and the maximum channel mobility were almost independent of Cbc. The conduction mechanism of the buried-channel MOSFETs is discussed in this paper.