Satoshi Ohkubo

High-Density Layer at the SiO2/Si Interface Observed by Difference X-Ray Reflectivity

We have developed a high-accuracy difference X-ray reflectivity (DXR) method using intense synchrotron radiation for the evaluation of ultrathin thermal oxides on Si(100). By carefully analyzing DXR data for gate oxides with thicknesses of 40 A and 70 A grown at 800° C to 1000° C, the existence of a dense ( ~2.4 g/cm3), thin (~10 A) layer at the SiO2/Si interface has been revealed. The thickness of the interfacial layer decreases with increasing oxidation temperature. Oxides grown in O3 or HCl/O2 have a thinner interfacial layer compared to those grown in O2.

Thermal oxide growth at chemical vapor deposited SiO2/Si interface during annealing evaluated by difference x-ray reflectivity

The x-ray interference technique has been applied to evaluate the structural changes of high temperature grown chemical vapor deposited (CVD) SiO2 film under several post annealing conditions. In annealing above 800 °C in O2 ambient, a thermal oxide growth has been found at the CVD SiO2/Si interface, and its precise thicknesses have been determined. The estimated diffusion coefficient of the oxidant in CVD film was about three times larger compared to that of thermal oxide. A threshold voltage shift in the oxide was found to strongly correlate to the thickness of the thermal oxide rather than to thermal modifications of the CVD SiO2 itself.

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.

Structural relaxation of SiO2/Si interfacial layer during annealing

Abstract We have studied the structural evolution of the high density interfacial layer around 10 A thick in 40 A thermal oxide observed by difference X-ray reflectivity (DXR) techniques during thermal annealing. Effects of interfacial stress are evaluated by grazing incidence X-ray diffraction. As the annealing proceeds, density of the interfacial layer decreased and got close to the value of the upper SiO 2 layer after 2 h of annealing in Ar at 800°C. At the same time, a slight increase in the thickness of the interfacial layer and the flattening of the Si interface are observed. These results indicate that during annealing, both the structural relaxation of oxide in the direction normal to the interface and an atomic rearrangement at the Si interface proceeds. Elastic deformation by stress can not be the dominant origin of the density change. The observed decrease of the interface state density D it along annealing may be linked to the decrease of structural defects accompanied with the structural relaxation at the interface.

Dry Cleaning for Fe Contaminants on Si and SiO2 Surfaces with Silicon Chlorides

While investigating the surface dependence of the dry cleaning technique using Cl radicals generated with UV irradiation (UV/Cl 2 , we found that silicon chlorides [SiCl x (x = 1 to 4)], etching products created from a reaction between Si and Cl radicals, can remove Fe contaminants. SiCl 4 gas removes Fe contaminants existing on both Si and SiO 2 surfaces without surface dependence. The surface residue due to the adsorption of SiCl 4 is insignificant. We also found that a small addition of Cl 2 to SiCl 4 is advantageous for dry cleaning Si surfaces. Surface flatness and composition are maintained after cleaning with Cl 2 + SiCl 4 (5:195 ml/min) gas mixture. Dry cleaning technology has been significantly improved by the use of an SiCl 4 -based system instead of Cl 2 alone.

Impact of Nitrogen Profile in Gate Oxynitride on Complementary Metal Oxide Semiconductor Characteristics

We demonstrated that the control of the nitrogen profile in the gate oxynitride for complementary metal oxide semiconductors (CMOSs) is very important. We grew NO or N2O nitrided gate oxide at 800°C or 900°C to prepare three kinds of oxynitrides with different nitrogen profiles, and investigated the atomic configuration and the chemical state of nitrogen using secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. Furthermore, we fabricated CMOS field effect transistors with gate oxide and oxynitride, and evaluated the interface state density and the hot carrier immunity. By systematical investigation of the relationship between the nitrogen profile and the electrical characteristics, we found that the nitrogen in the oxynitride should exist only at the interface for realizing the CMOS devices having high performance and high reliability.

X-Ray Reflectometry and Infrared Analysis of Native Oxides on Si(100) Formed in Chemical Treatment

We determined the absolute density of oxides on Si by glancing incidence X-ray reflecomety (GXR) for the first time. The chemical structurcs were revealed by FI-IR analysis and compared with the physical structues. l,ow-density and inhomogeneity were found in some conventional chemical oxides. We show that dense and chemically-homogeneous oxides could be prepared by ozonized water, a candidate for a fearure cleaning solution.

High quality ultra-thin (4 nm) gate oxide by UV/O/sub 3/ surface pre-treatment of native oxide

A significant improvement in ultra-thin (4 nm) gate oxide quality has been carried out using UV/O/sub 3/ pre-treatment of native oxide before thermal oxidation. UV/O/sub 3/ pre-treatment makes native oxide dense and close-packed without leaving any residue species. Ultra-thin gate oxide formed by UV/O/sub 3/ pre-treatment and O/sub 3/ oxidation has been found to have excellent behavior, low leakage current, low surface state density, and superior dielectric breakdown characteristics. UV/O/sub 3/ pre-treatment looks promising for using in ultra-thin gate oxidation necessary for 0.1 /spl mu/m ULSI fabrication.

MOVPE Growth of GaAs on Si Using Tertiarybutylarsine

We developed GaAs heteroepitaxy on a Si substrate by metalorganio vapor phase epitaxy (MOVPE) using tertiarybutylarsine (TBAs). When we preheated Si at 1000oC in the atmosphere including TBAs, a carbide layer was formed on the Si surface. This led to polycrystalline GaAs growth. By carrying out high-temperature preheating in an H 2 -only atmosphere and supplying TBAs after the preheating, we have successfully grown single-crystal GaAs with a mirror surface in a process completely free of AsH 3 .