研究発表

A novel plasma co-polymerization technology, using flexibly-mixed molecular gas of chain-type vinyl-siloxane and 6-membered ring-type one, has been developed for new Seamless Low-k SiOCH Stacks (SEALS). An ultimate high-modulus silica-amorphous-carbon-composite (SACC)-SiOCH film with 24.8GPa was realized by 100%-injection of the chain-type siloxane, adapting to the hard-mask on molecular-pore-stack (MPS) SiOCH film (k=2.45, 3.0GPa) from 100%-injection of the ring-type siloxane. For the via-dielectrics was utilized a new co-polymerized (CP) SiOCH film (k=2.8, 12.6GPa) from these gas mixture to enhance the mechanical strength. The in-situ sequential deposition of three kinds of films without air-break accomplished excellent adhesion, high quality interface and low O2 ashing damage. The fully-scaled-down, 32nm-node Cu interconnects achieved 83fF/mm (single-load) in 100nm-pitched Cu lines with the new co-polymerized SEALS.

By a novel oxygen absorption process, low oxygen-content Cu-alloy is implemented for fully-scaled-down, 45 nm-node dual damascene interconnects (DDIs) with 140 nm-pitched lines and 70 nmø-vias. In this process, a very thin metal film as an oxygen absorber, which has larger negative change in the standard Gibbs free energy of oxidation than a barrier metal, is put on a natural oxide at a surface of electro-plated, Cu film. The oxygen atoms diffuse to the oxygen absorber, not to the barrier metal under the Cu film, achieving high quality Cu/barrier interface after annealing. Combining the oxygen absorption process with Cu-alloy process, 45 nm-node DDI in molecular-pore-stacking (MPS) SiOCH film is successfully obtained with high endurances for SIV, EM and TDDB. © 2005 IEEE.

Hybrid-type, Cu dual damascene interconnects (DDI) are fabricated in a porous organosilica film (k = 2.1) inserted between low-k films of hard-mask (HM) and etch-stop (ES) layers. Plasma-polymerized, divinyl siloxane bis-benzocyclobutene (p-BCB, k = 2.7) film, instead of SiCN film (k > 4), is selected for these HM and ES layers due to the low k-value as well as the high etch-stop property to the porous film. The line capacitance in the hybrid-type, Cu-DDI with BCB-HM and BCB-ES layers decreases 20% compared with that of the Cu-DDI with SiO2-HM and SiCN-ES layers, achieving the effective dielectric constant (keff) of 2.6. This new interconnect structure is a strong candidate for the 70 nm-node ULSIs.

Solid-electrolyte crossbar switch (namely NanoBridge) with low programming current of 420μA and highly reliable ON state against pulsed-alternating current (AC) stress is demonstrated under practical operating conditions of a programmable logic device (PLD). The ON-state duration under a pulsed-AC stress is achieved >10 years at 150°C. The high reliability under AC originates from the fact that the stress induced by Cu+ ion migration at a negative bias is recovered by a positive bias. NanoBridge is applicable in a scaleddown, nonvolatile PLD for hp28 and beyond. © 2010 IEEE.

This paper proposes the utility of the solid-electrode nanometer switch device called atom switch for ultra-low voltage EEPROM of near- or sub-60mV/dec. steep subthreshold slope transistors. We adopt combination of a simple inverter-sensing read circuit and the atom switch device. This circuit does not include sense amplifiers and not limited by operation limit of analog circuits. High on-off ratio and off resistance enable low-voltage operation with a simple inverter-sensing structure. We fabricated a TEG wafer in a 65nm process, and obtained measurement results of circuit operation in 350mV including the level shifter of memory cell selector driver and in 150mV with the read circuit only. © 2014 IEEE.

For the first time, a 40nm-node, 2x logic density, 3.8x operation speed, and 3x power efficient, nonvolatile programmable logic (NPL) is demonstrated by using Cu atom switch for configuration switches. The switching characteristics of the atom switch are kept in scaling down to 64/32nm device area, and an improved PSE reduces set voltage while keeping low leakage current, enabling core transistors to select the atom switches. The developed 40nm NPL is a strong candidate for the next wave of energy-efficient computing.

We propose a new approach for improving the operating margin of Ta 2O5/plasma oxidized TiO2 stacked unipolar ReRAM. It was found that the reset voltage (switching from low resistance state to high resistance state) can be minimized by using local minimum against the resistance of the low resistance state. In addition, weakening the plasma oxidation condition reduced the power consumption and the variation of reset voltage. Excellent operating margin and more than 105 switching cycle times was successfully demonstrated using the integrated device. © 2010 IEEE.

Sputter deposited GexSe1-x films are characterized, prior to device fabrication for a selector. A Se-rich film has GeSe4/2 tetrahedral structure and higher crystallization temperature than Ge-rich films. Printed Ag-paste electrodes are used for I-V measurement and an amorphous Se-rich GexSe1-x film shows the good switching property for the selector with an on/off ratio of 4.8 × 104.