Kei Horiuchi

Atomic Step Structure on Vicinal H/Si(111) Surface Formed by Hot Water Immersion

We investigated the hydride structures at the step edges on Si(111) surfaces after removing surface oxide with HF solution followed by immersion in boiling water, using polarized infrared attenuated total-reflection spectroscopy. Vicinal (111) surfaces misoriented toward the [11] direction at angles of 0°, 2°, and 4° were used to elucidate the hydride structures at the steps. We assigned absorption peaks to monohydride chains at the step edges along the [10] direction, vertical dihydride (whose three atoms form a surface vertical to [111]) at the kinks, and monohydride on the terraces. We determined that the silicon monohydride chain forms an atomically straight step edge along the [10] direction with a small amount of vertical dihydride kinks after 5-min immersion in boiling water. Based on these assignments, we reexamined the water temperature and time dependence of these hydride structures and discussed the step formation mechanism.

Flat-band voltage shifts in p-MOS devices caused by carrier activation in p/sup +/-polycrystalline silicon and boron penetration

We found that the annealing time dependence of the flat-band voltage (V/sub FB/) shift of a p/sup +/-polysilicon gate MOS diode is attributed to the activation of boron in the polysilicon instead of the boron penetration through the gate SiO/sub 2/. We identified the process window for p/sup +/-polysilicon gate pMOSFETs taking into account that boron is sufficiently activated in polysilicon without penetrating through the gate SiO/sub 2/.

Boron Diffusion in Nitrided-Oxide Gate Dielectrics Leading to High Suppression of Boron Penetration in P-MOSFETs

Nitrided-oxide gate dielectrics have been proposed to suppress boron penetration in deep submicron metal-oxide-semiconductor field effect transistors (MOSFETs). However, few quantitative reports have been released on how nitrided oxides enlarge the permissible thermal budget. We evaluated the diffusivities of a nitrided oxide formed by annealing SiO2 in NO gas and demonstrated that this film enables us to use BF2+ for scaled devices. We also proposed a model depicting boron penetration through the nitrided-oxide layer.

Nitrogen Concentration Dependence on Boron Diffusion in Thin Silicon Oxynitrides Used for Metal‐Oxide‐Semiconductor Devices

The effect of nitrogen concentration on boron diffusion in silicon oxides (oxynitride) used for metal-oxide-semiconductor structures was investigated. The oxynitrides, which were formed by oxidizing thin, thermally grown nitrides, contained uniform amounts of nitrogen. The boron diffusion coefficients in the oxynitrides were determined, and experimental and simulated results were compared. The diffusion coefficients have an Arrhenius relationship to each concentration of nitrogen, and are smaller in higher nitrogen concentrations. A 25% concentration of nitrogen exhibited an oxynitride diffusion coefficient at least two orders smaller than that of SiO 2 . The higher the nitrogen concentration was, the larger the activation energy was. The diffusion coefficient data is useful for evaluating the boron penetration of various types of oxynitrides, including nitrided oxides. An empirical diffusion model is proposed in order to explain the experimental data qualitatively.

Boron Diffusion in SiO2 Involving High-Concentration Effects

The diffusivity of boron in gate SiO2 increases with the concentration of boron in the polysilicon gates. A model is described that can explain both the thickness and annealing-time dependencies of the boron penetration in p-channel metal-oxide-semiconductor devices.

Hydrogen-Enhanced Boron Penetration in PMOS Devices during SiO2 Chemical Vapor Deposition

We demonstrated that boron penetration through gate oxides is more significant in a SiO2 chemical vapor deposition ambient than in a N2 ambient. By systematically evaluating hydrogen concentration dependence on boron diffusivity in gate dielectrics, we determined that enhanced boron diffusion through gate oxides was attributable to hydrogen in the SiO2 chemical vapor deposition source gas.

Synchrotron radiation-assisted silicon film growth by irradiation parallel to the substrate

Growth of silicon films by synchrotron radiation (SR) photolysis of Si2H6 is studied for temperatures below 500°C. SR is irradiated parallel to the substrate to grow silicon film over a large area and to avoid substrate heating and gas dissociation by photoelectrons. The thickness uniformity in a 2-inch wafer is over 50% while an SR cross section is about 1×10 mm. At substrate temperatures above 300°C, the hydrogen content of the film is low enough that epitaxial silicon film is successfully grown.

Sub-100 nm device fabrication using proximity X-ray lithography at five levels

Proximity X-ray lithography (PXL) is a promising technology for fabricating ultra-large-scale integrated (ULSI) devices smaller than 100 nm because it offers high-resolution capabilities and dimensional control with high throughput. We used PXL at five levels (mark, isolation, gate, contact, wiring) and fabricated 100-nm complicated dense patterns and sub-100-nm channel length MOSFETs. In this paper, we discuss lithographic performance and the performance of the MOSFET device.

Synchrotron radiation‐assisted silicon homoepitaxy at 100 °C using Si2H6/H2 mixture

Epitaxial silicon film is deposited on a Si(100) substrate by synchrotron radiation irradiation. Reflection high‐energy electron diffraction and high‐resolution transmittance electron microscopy observation reveal that epitaxial growth can be realized at temperatures as low as 100 °C. At substrate temperatures above 300 °C, the films show a clear 2×1 reconstructed surface, indicating a fairly good crystal quality. Below 500 °C, the growth rate increases as the substrate temperature is lowered, meaning that the surface adsorption of source gas and/or photogenerated radicals plays an important role in the epitaxial growth reaction.

Study of the Etching Reaction by Atomic Chlorine Using Molecular Beam Scattering

We studied the interaction of atomic chlorine with Si(100)2×1 surfaces using atomic chlorine beams. Above 600° C, the etching reactions with molecular or atomic chlorine were the same, therefore we studied reactions below 600° C. Most of the desorption products were SiCl2, but some higher silicon chlorides, such as SiCl4 or Si2Cl6, also desorbed from the surface. Our study of the temperature dependence of the SiCl2 desorption reaction showed that the activation energy is 0.08 eV at 0.4 monolayers (ML) and 0.2 eV at 0.8 ML. These extremely low activation energies suggest that the surface reaction is mainly driven by the kinetic or chemical potential energy of incident atomic chlorine instead of thermal excitation from the Si(100) surface. The reaction depends on the surface chlorine coverage, with the reaction occurring above 0.3 ML, reaching a maximum at 0.4 ML, and decreasing as the coverage increases further.