Carbon nanotube vias for multilevel interconnects using CMP techniques

We have developed carbon nanotube (CNT) vias using thermal chemical vapor deposition (CVD) at a growth temperature of 450°C with cobalt catalysts, titanium carbide ohmic contacts, and tantalum barrier layers on copper wiring. The total resistance of the CNT via comprised of about 1, 000 tubes, was three orders of magnitude lower than that of one CNT, indicating that the current flows in parallel, through the tubes. We have also demonstrated a mechanical polishing technique for CNT vias. The 1-μm-high outprojecting CNTs were polished using a diamond slurry of 30-μm-diameter particles mixed in oil at pressures below 18 kPa. Because the adhesion strength of the CNTs was about 5.5 MPa, the CNT vias were able to withstand the mechanical stress applied during the polishing process.