Naruhiko Nakanishi

Hexagonal polymorph of tantalum–pentoxide with enhanced dielectric constant

A tantalum–pentoxide dielectric with an enhanced permittivity of over 50 was found to be crystallized in a hexagonal symmetry with a=0.628 nm and c=0.389 nm. The incommensurate epitaxy of tantalum pentoxide on hcp-ruthenium metal stabilizes the hexagonal phase with √3-time periodicity in plane, as compared with that of the known hexagonal δ phase. The crystallographic assumption, which is based on one-dimensional Ta–O–Ta chain along the c axis, can explain large polarizability caused by delocalized electrons on the one-dimensional chain.

Novel Storage-Node Contacts with Stacked Point-Cusp Magnetron Sp-TiN Barrier for Metal–Insulator–Metal Ru/Ta2O5/Ru Capacitors in Gigabit Dynamic Random Access Memories

We have investigated a mechanism for increasing the contact resistance (Rc) of the ruthenium (Ru) and the titanium nitride (TiN) barrier during the tantalum oxide (Ta2O5) oxidation annealing in the metal–insulator–metal (MIM) capacitors. It has been found that controlling the atomic ratio of Ti to N (Ti/N ratio) is a key to keeping the contact resistance low. Controlling the Ti/N ratio is easy for the sp-TiN, while it is difficult for the chemical-vapor-deposited TiN. On the basis of this result, we have proposed a novel Ru/TiN contact with a stacked-barrier structure fabricated by using the point-cusp magnetron (PCM) sputtering method. We have applied this structure to the MIM-Ru/Ta2O5/Ru capacitor in a gigabit DRAM with 0.10 µm design. In this capacitor, we have obtained the contact resistance of 10 kΩbit and the capacitor leakage current of 10-17 A/bit in the range of -1 to +1 V.