Toyohiro Chikyo

Effective-Work-Function Control by Varying the TiN Thickness in Poly-Si/TiN Gate Electrodes for Scaled High-

We have investigated the controllability of the effective work function (phim,eff) of TiN as a work-function-determining metal (WFM) for various gate-electrode structures in HfSiON MOSFETs. phim,eff was controllable from 4.7 to 4.44 eV by changing the TiN thickness from 30 to 2 nm in poly-Si/TiN gate electrodes, without any distinct increase in EOT. Therefore, thin-TiN and thick-TiN WFMs are preferred for the reduction in threshold voltage in nMOSFETs and pMOSFETs with poly-Si/TiN gate electrodes, respectively. A similar controllability was not observed with W/TiN gate electrodes but was evident with W/TaSiN/TiN gate electrodes. This means that controllability is a characteristic of metal gate electrodes with a structure including a Si-rich layer (such as poly-Si and TaSiN)/TiN. It is considered that Ti suboxides, which increase phim,eff as a thin insulator with negative fixed charges, or interface dipoles in the TiN/HfSiON interface, are reduced by oxidation of the Si-rich layer, producing the required result of phim,eff decrease when the TiN thickness becomes as thin as 2 nm.

k

Metal-insulator-semiconductor field-effect transistors (MISFETs) with aluminum oxide as a gate insulator have been fabricated on a hydrogen-terminated diamond surface using its surface conductive layer. The aluminum oxide gate insulator was deposited on the diamond surface by the pulsed laser deposition method. The on-off ratio measured by dc was greater than five orders of magnitude, one of the best results reported for diamond FETs. The gate leak current of aluminum oxide MISFETs is three orders of magnitude less than that of conventional CaF2 MISFETs. These characteristics indicate that aluminum oxide gate insulators are suitable for high reliability power device applications of diamond MISFETs.

CMOSFETs

Density functional calculations are performed for lanthanum-oxide clusters in order to study the local dielectric properties of such clusters using the dielectric constant defined at local points. An increase in coordination number brings about an increase in electron population on the central lanthanum atom, leading to an increase in the local dielectric constant.

Characterization of diamond metal-insulator-semiconductor field-effect transistors with aluminum oxide gate insulator

Electron field emission (eFE) from sp3-bonded 5H‐BN films proved to take place in air at an atmospheric pressure. The eFE started at relatively low electric field (E) of 7.5V∕μm and was reproducible. The eFE in air obeyed the Fowler-Nordheim equation for quantum mechanical tunneling. The BN films with self-organized microcone emitters were prepared by chemical vapor deposition from B2H6+NH3+Ar plasma where 193nm excimer laser irradiated the growing film surface. The laser activates the growth reactions photochemically and induces the cone-shape formation. The eFE from the same sample observed in vacuum showed the threshold E below 1V∕μm. These excellent eFE properties are considered to originate from geometrical field enhancement by the microcone shape and the decrease of work function due to the surface electric dipole moment layer (4.3eV, estimated by molecular orbital method). This atmospheric eFE combined with the robustness of BN may open a wide range of applications.

Electronic Structure Study of Local Dielectric Properties of Lanthanoid Oxide Clusters

The authors studied the characteristics of Si/Al2O3/(Ta/Nb)Ox/Al2O3/SiO2/Pt charge trap capacitors fabricated by atomic layer deposition and postmetallization annealing at 400 °C. Al2O3 and (Ta/Nb)Ox films are amorphous and have negligible fixed charges. In program mode, a flatband voltage (Vfb) drastically shifts toward the positive direction at a short program time of 10−4 s. A large Vfb shift of approximately 4 V arises after programming at 1 mC/cm2 because there is a large difference in the conduction band offset between the (Ta/Nb)Ox-charge trapping layer (TNO-CTL) and the Al2O3-blocking layer (AlO-BL) (1.8 eV). In the retention mode, most of the trapped electrons in the TNO-CTL transfers across the Al2O3-tunneling layer (AlO-TL) rather than the AlO-BL. The thickness of the AlO-TL affects the Vfb shift degradation behavior in the retention mode. The injected electrons are dominantly located at the TNO-CTL/ALO-BL interface, determined from the thickness dependence of the TNO-CTL on the Vfb shift.

Electron field emission in air at an atmospheric pressure from sp3-bonded 5H‐BN microcones

In this paper, the authors studied anatase TiO2 films, fabricated by using atomic layer deposition and postdeposition annealing (PDA). The as-grown TiO2 films were of high purity; the carbon and nitrogen contents were within the x-ray photoelectron spectroscopy detection limit of 3–5 at. %. The anatase TiO2 film fabricated by PDA at 500 °C in O2 had a very high dielectric constant of >30 and was of high quality because it exhibited no hysteresis at its flatband voltage (Vfb) and contained negligible defect charge. The positive Vfb shift of anatase TiO2 (0.08 V), caused by the bottom interface dipole at a TiO2/SiO2 interface, was much smaller than those of Al2O3 (0.72 V) and HfO2 (0.29 V). However, the maximum Vfb change of the anatase TiO2 was greater than those of HfO2 and HfSiOx because the TiO2 contained more oxygen than the other materials.

Role of the (Ta/Nb)Ox/Al2O3 interface on the flatband voltage shift for Al2O3/(Ta/Nb)Ox/Al2O3 multilayer charge trap capacitors

A heterojunction of p-type sp3-bonded boron nitride (BN) and n-type Si fabricated by laser–plasma synchronous chemical vapour deposition (CVD) showed excellent rectifying properties and proved to work as a solar cell with photovoltaic conversion efficiency of 1.76%. The BN film was deposited on an n-type Si (1 0 0) substrate by plasma CVD from B2H6 + NH3 + Ar while doping of Si into the BN film was induced by the simultaneous irradiation of an intense excimer laser with a pulse power of 490 mJ cm−2, at a wavelength of 193 nm and at a repetition rate of 20 Hz. The source of dopant Si was supposed to be the Si substrate ablated at the initial stage of the film growth. The laser enhanced the doping (and/or diffusion) of Si into BN as well as the growth of sp3-bonded BN simultaneously in this method. P-type conduction of BN films was determined by the hot (thermoelectric) probe method. The BN/Si heterodiode with an essentially transparent p-type BN as a front layer is supposed to efficiently absorb light reaching the active region so as to potentially result in high efficiency.

Electrical properties of anatase TiO2 films by atomic layer deposition and low annealing temperature

A bias application in hard X-ray photoelectron spectroscopy can successfully elucidate the bias-dependent electronic structures in devices. To demonstrate the versatility of this method, we investigated a Ru/HfO2/SiO2/Si structure as a prototype and directly observed the bias-dependent electronic states while keeping the device structure intact.

P-type sp3-bonded BN/n-type Si heterodiode solar cell fabricated by laser–plasma synchronous CVD method

The gate leakage behaviors of p- and n-type metal-oxide-semiconductor (p−∕nMOS) capacitors with hafnium silicon oxynitride (HfSiON) gate dielectric were microscopically investigated by electron-beam-induced current (EBIC) technique. Carrier separated EBIC measurement has found that in nonstressed samples, hole conduction in pMOS is significantly enhanced by trap-assisted tunneling, while electron conduction in nMOS is independent of traps. After voltage stress, traps are induced in nMOS and enhanced electron conduction.

New Direct Spectroscopic Method for Determination of Bias-Dependent Electronic States: Hard X-ray Photoelectron Spectroscopy Under Device Operation

Although gate stack structures with high-k materials have been extensively investigated, there are some issues to be solved for the formation of high quality gate stack structures. In the present study, we employed hard x-ray photoelectron spectroscopy in operating devices. This method allows us to investigate bias dependent electronic states, while keeping device structures intact. Using this method, we have investigated electronic states and potential distribution in gate metal/HfO2 gate stack structures under device operation. Analysis of the core levels shifts as a function of the bias voltage indicated that a potential drop occurred at the Pt/HfO2 interface for a Pt/HfO2 gate structure, while a potential gradient was not observed at the Ru/HfO2 interface for a Ru/HfO2 gate structure. Angle resolved photoelectron spectroscopy revealed that a thicker SiO2 layer was formed at the Pt/HfO2 interface, indicating that the origin of potential drop at Pt/HfO2 interface is formation of the thick SiO2 layer at ...