Hirotaka Hamamura

Electro-luminescence from ultra-thin silicon

Ultra-thin single crystal silicon with the (100) surface formed by the local-oxidation-of-silicon (LOCOS) on a silicon-on-insulator (SOI) substrate becomes a quasi-direct band-gap semiconductor due to the quantum mechanical confinement effect. The device is a simple pn diode in a planar structure. Electro-luminescence (EL) has been observed by the lateral carrier injections into the two-dimensional quantum well.

Growth mechanism of nanoparticles prepared by radio frequency sputtering

Growth mechanisms of nanometer-sized particles prepared by rf sputtering on silica glass layers were examined. Gold and gallium arsenide (GaAs) particles synthesized with varying sputtering times on a SiO2 sputtered layer were subsequently buried in a SiO2 film by sputtering a SiO2 target. Transmission electron microscopy showed that in both cases, with increasing sputtering time, the number density decreased and the distance between neighboring particles increased in the initial stage of the growth, which suggests that the particles migrate on the SiO2 surface and coalesce with each other as they grow. Differences of GaAs and gold particle formation suggest that the mobility of the GaAs particles is much larger than that of gold. The results suggest that the migration of nanoparticles is activated by the bond-formation energy released during the incorporation of precursors into growing particles.

Silicon light-emitting transistor for on-chip optical interconnection

The authors propose a light-emitting field-effect transistor with the active layer made of the ultrathin single crystal silicon with the (100) surface orientation. The ambipolar carrier injections from the highly impurity doped regions to the ultrathin silicon are achieved in complementary-metal-oxide-semiconductor compatible planar structures and the optical intensities are controlled by the gate voltage. By using the device, they have demonstrated that a simple electrical signal can be transferred by light and detected on the same silicon chip as photocurrents controlled by the gate bias.

Effects of remote-surface-roughness scattering on carrier mobility in field-effect-transistors with ultrathin gate dielectrics

We examined effects of the remote surface roughness, which is the roughness between the polycrystalline silicon gate and gate dielectric, on the inversion carrier mobility of metal-insulator-semiconductor field-effect-transistors with ultrathin gate dielectrics. We calculated the effective mobility by the linear response theory and found that the scattering from the remote surface roughness reduces the effective mobility especially at high vertical fields. The effective mobility is severely reduced, if the correlation length of the remote surface roughness is comparable to the inverse of thermal de Broglie wave number. We show that the hole mobility reduction experimentally found for the transistor with the Al2O3 gate dielectric can be explained by this scattering.

Slowing single-stranded DNA translocation through a solid-state nanopore by decreasing the nanopore diameter

To slow the translocation of single-stranded DNA (ssDNA) through a solid-state nanopore, a nanopore was narrowed, and the effect of the narrowing on the DNA translocation speed was investigated. In order to accurately measure the speed, long (5.3 kb) ssDNA (namely, ss-poly(dA)) with uniform length (±0.4 kb) was synthesized. The diameters of nanopores fabricated by a transmission electron microscope were controlled by atomic-layer deposition. Reducing the nanopore diameter from 4.5 to 2.3 nm slowed down the translocation of ssDNA by more than 16 times (to 0.18 μs base(-1)) when 300 mV was applied across the nanopore. It is speculated that the interaction between the nanopore and the ssDNA dominates the translocation speed. Unexpectedly, the translocation speed of ssDNA through the 4.5 nm nanopore is more than two orders of magnitude higher than that of double-stranded DNA (dsDNA) through a nanopore of almost the same size. The cause of such a faster translocation of ssDNA can be explained by the weaker drag force inside the nanopore. Moreover, the measured translocation speeds of ssDNA and dsDNA agree well with those calculated by molecular-dynamics (MD) simulation. The MD simulation predicted that reducing the nanopore diameter to almost the same as that of ssDNA (i.e. 1.4 nm) decreases the translocation speed (to 1.4 μs base(-1)). Narrowing the nanopore is thus an effective approach for accomplishing nanopore DNA sequencing.

TiN Films Prepared by Flow Modulation Chemical Vapor Deposition using TiCl4 and NH3

We propose a new chemical vapor deposition (CVD) process, the flow modulation chemical vapor deposition (FMCVD) process, to obtain high quality titanium nitride (TiN) films at low deposition temperature in a single CVD chamber. FMCVD uses sequential deposition and reduction processes, such as the deposition of TiN films followed by chlorine reduction. This cycle was repeated to achieve sufficient film thickness. By decreasing the thickness in one cycle, the residual chlorine concentration and the resistivity of the films decreased. Using FMCVD process, we could achieve low resistivity (250 µΩcm), low residual chlorine concentration (2 at.%) with uniform step coverage at low deposition temperature (380°C).

An ultra-thin silicon nitride gate dielectric with oxygen-enriched interface (OI-SiN) for CMOS with EOT of 0.9 nm and beyond

We demonstrate a SiN gate dielectric with oxygen-enriched interface (OI-SiN). A process in which oxygen atoms are incorporated after forming SiN provides enhanced nitrogen concentration and oxygen-enriched interface simultaneously even in the region of EOT < 1.5 nm. Thus we developed an OI-SiN gate dielectric with EOT of 0.9 nm that brought about low gate leakage current, good interface properties and excellent resistance to boron penetration.

Adhesion characteristics between chemical vapor deposited Cu and TiN films: Aspects of process integration

This paper examines the properties of Cu films deposited on different TiN substrates. The TiN substrates were prepared using TiCl4/NH3 chemistry based chemical vapor deposited (CVD) TiN process by varying the preparation methods and temperatures. Properties examined include morphology and crystallinity as well as adhesion characteristics of the Cu films on the TiN substrates. It was found that the Cu film properties were strongly affected by the overall stress in the multi-layer structure and the amount of residual chlorine (Cl) in the TiN film. When the stress conditions of the Cu and TiN films are the same, good adhesion occurred. Higher Cl concentrations caused adhesion enhancement of the Cu film; however, surface morphology was degraded. Angle resolved X-ray photoelectron spectroscopy (XPS) results and depth analysis implied that fast Cu diffusion occurred in the near-interface region. It is suggested that Cl enhances the diffusion of Cu, resulting in the formation of a diffusion interface that improves adhesion.

Structural change of TiN/Ti/SiO2 multilayers by N2 annealing

Abstract We investigated the structural change of TiN/Ti/thick SiO2 multilayers as a function of annealing temperature by X-ray diffraction (XRD), transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). XRD analysis and N concentration profiles determined by SIMS showed that the initial Ti(002) film changes to TiN (111) at annealing temperatures higher than 450°C. TEM observations revealed that the interface between TiN and Ti become less distinct at annealing temperatures higher than 450°C, and we found an amorphous layer at the interface between the Ti and the SiO2 layer. The O concentration profile determined by SIMS suggested that this layer was mainly TiOx.

Thickness-dependent dielectric breakdown and nanopore creation on sub-10-nm-thick SiN membranes in solution

Recently, dielectric breakdown of solid-state membranes in solution has come to be known as a powerful method for fabricating nanopore sensors. This method has enabled a stable fabrication of nanopores down to sub-2 nm in diameter, which can be used to detect the sizes and structures of small molecules. Until now, the behavior of dielectric breakdown for nanopore creation in SiN membranes with thicknesses of less than 10 nm has not been studied, while the thinner nanopore membranes are preferable for nanopore sensors in terms of spatial resolution. In the present study, the thickness dependence of the dielectric breakdown of sub-10-nm-thick SiN membranes in solution was investigated using gradually increased voltage pulses. The increment in leakage current through the membrane at the breakdown was found to become smaller with a decrease in the thickness of the membrane, which resulted in the creation of smaller nanopores. In addition, the electric field for dielectric breakdown drastically decreased when ...