Youhei Sugimoto

Low-temperature fabrication of polycrystalline Si thin film using Al-induced crystallization without native Al oxide at amorphous Si/Al interface

Low-temperature fabrication of polycrystalline silicon (poly-Si) thin film has been performed by Al-induced crystallization (AIC), and the structural properties have been investigated. In our experiments, to prevent native oxidation of Al film, an amorphous silicon (a-Si)/Al bilayer was formed on the SiO2/Si substrate by electron beam evaporation without breaking the vacuum. The a-Si/Al/SiO2/Si structure was then heated at a low temperature of 400°C to induce AIC. It was confirmed that layer exchange of the a-Si/Al bilayer is induced even though there is no native oxidation of Al film, which was demonstrated by scanning transmission electron microscopy and energy dispersive X-ray analysis. The mechanism for layer exchange of the a-Si/Al bilayer has been discussed. Furthermore, it was verified by scanning electron microscopy and spectroscopic ellipsometry that the a-Si/Al thickness ratio of roughly 1:1 is suitable to achieve a flat surface morphology of poly-Si. In addition, it was found, by X-ray diffraction and orientation imaging microscopy, that the Si(111)-oriented grain becomes dominant with decreasing thickness of the a-Si/Al bilayer.

Effective work function modulation of TaN metal gate on HfO2 after postmetallization annealing

The effective work function (Φm,eff) of TaN on HfO2 after postmetallization annealing (PMA) was investigated using TaN∕HfO2∕SiO2∕Si as a sample structure. We found that Φm,eff on HfO2 is stable at PMA temperatures of less than 600°C and is 4.6eV, which is approximately 0.2eV higher than that on SiO2. In contrast, Φm,eff is modulated by PMA at temperatures greater than 750°C. An analysis by x-ray photoelectron spectroscopy suggests that the increased Φm,eff is strongly related to Ta oxide formation near the TaN∕HfO2 interface. The modulation of Φm,eff on HfO2 is discussed on the basis of intrinsic and extrinsic Fermi level pinning due to Ta–O bond formation at the TaN∕HfO2 interface.

Electrical and Structural Properties of TaN Gate Electrodes Fabricated by Wet Etching Using NH4OH/H2O2 Solution and Hf Metal Hard Mask

We fabricated TaN gate electrodes on SiO2 film by wet etching using NH4OH/H2O2 solution and investigated the electrical and structural properties of the TaN/SiO2 interfacial layer. Hf metal was used as a hard mask for the wet etching of the TaN film. It was found that the gate patterning of the TaN film was successfully achieved by wet chemical etching, which should be applicable for dual-metal-gate fabrication. The effective fixed charge density (Qeff) into the SiO2 film and the effective work function (Φm,eff) of TaN remained constant after N2 annealing at temperatures of up to 750 °C but increased after annealing at 900 °C. The analysis by X-ray photoelectron spectroscopy (XPS) indicated that Ta oxide was formed near the TaN/SiO2 interface after the annealing at 900 °C. The increases in Qeff and Φm,eff are discussed on the basis of the XPS results.

Effect of Ion Mass and Ion Energy on Low-Temperature Deposition of Polycrystalline-Si Thin Film on SiO2 Layer by Using Sputtering-Type Electron Cyclotron Resonance Plasma

Polycrystalline-Si thin film was successfully deposited on a SiO2 layer by using a sputtering-type electron cyclotron resonance plasma at the low substrate temperature of 400°C. The effects of ion (Ar, Kr, and Xe) mass and radius on the crystallization of deposited Si films were studied. Ions having a large mass and radius contributed more effective energy to Si atoms and thus crystallization was enhanced. The effect of substrate DC-bias for control of ion energy was also clarified. DC substrate bias voltage of (-)50 V for the Xe plasma was found to be most suitable for polycrystalline-Si growth.

Electrical and structural evaluations of high-k gate dielectrics fabricated using plasma oxidation and the subsequent annealing for a Hf/SiO2/Si structure

High-permittivity (high-k) dielectrics with HfO2/HfxSi1−xOy/Si structures were fabricated using plasma oxidation and the subsequent annealing for a Hf/SiO2/Si structure. By changing a SiO2 film in an initial structure from plasma oxidation at a low temperature to dry oxidation at a high temperature, the drastic decrease in the trap density in an interfacial layer (IL: HfxSi1−xOy) could be successfully achieved, which showed an interface state density of 1 × 1011 eV−1 cm−2, an effective oxide thickness (EOT) of 1.2 nm and four orders decrease in the leakage current density relative to SiO2 with the same EOT. The influence of post-annealing on structural and electrical properties of the IL was investigated by using x-ray photoelectron spectroscopy and a transmission electron microscope. It was clarified that the increase in EOT after post-annealing at 900 °C was caused by the decrease in Hf content in the IL and the increase in the IL thickness. The kinetics of the IL formation is discussed in detail. The effects of O2 gas ambience during post-annealing on EOT and flat-band voltage (Vfb) were investigated, which showed that the Vfb decreased with increasing O2 gas pressure while maintaining a low EOT.

Low-Temperature Growth of Thin Silicon Nitride Film by Electron Cyclotron Resonance Plasma Irradiation

An amorphous silicon nitride thin film has been fabricated by electron cyclotron resonance plasma irradiation. The growth of the film is carried out by Ar/N2 mixed plasma irradiation at a low temperature of 400°C. It is found that nitrogen partial pressure decisively affects film quality. A SiN film having a structure nearest to stoichiometric construction is obtained by precisely controlling the N2 mixing ratio at 60%. This implies that the existence of Ar with a suitable partial pressure increases the nitrogen radical concentration in the Ar/N2 mixed plasma. Under optimum conditions, the as-grown SiN film shows a leakage current more than two orders of magnitude lower than that of thermally grown SiO2 having the same equivalent oxide thickness. A high-resolution transmission electron micrograph shows an atomically flat interface of the Si substrate and SiN film.

Fabrication of high-k gate dielectrics using plasma oxidation and subsequent annealing of Hf/SiO 2 /Si structure

High-permittivity (high-k) dielectrics with HfO₂/Hf_xSi_1-xO_y/Si structures were fabricated using plasma oxidation and subsequent annealing of Hf/SiO₂/Si structure. By replacing SiO₂ film of initial structure from plasma oxidized SiO₂ to thermal oxidized SiO₂, the drastic decrease of traps in interfacial layer (IL: Hf_xSi_1-xO_y) could be successfully achieved, which shows interface state density of 1×10¹¹ eV^-1cm^-2, effective oxide thickness (EOT) of 1.2 nm, and 4 orders decrease of leakage current density relative to SiO₂ with EOT of 1.2 nm. The influence of post annealing on structural and electrical properties of IL was investigated by using XPS analysis and TEM observation. It was clarified that the increase of EOT after post annealing at 900°C is caused by the decrease of Hf content in IL and the increase of IL thickness. The kinetics of IL formation is discussed in details.