Kanetake Takasaki

Effect of fluorine on boron diffusion in thin silicon dioxides and oxynitride

We investigated the effects of fluorine on boron diffusion in thin silicon oxides used for metal‐oxide‐semiconductor structures, including silicon dioxide and oxynitride. We used secondary ion mass spectroscopy to measure the boron penetration depth from p+‐polycrystalline silicon to the silicon substrate through the silicon oxides for various fluorine doses. We compared experimental and simulated results and determined the boron diffusion coefficients in the silicon oxides. The diffusion coefficients have an Arrhenius relationship for each fluorine dose. The diffusion coefficients at a fluorine dose of 1×1016 cm−2 were 30 times larger than with no fluorine dose, and at a fluorine dose of 1×1015 cm−2, diffusion coefficients were 5 times larger. With oxynitride, fluorine has the same enhancing effect. With no fluorine, the diffusion coefficients were independent of oxide thickness. When fluorine is implanted into polycrystalline silicon, especially with a high dose, the diffusion coefficient is larger for ...

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.

High-Accuracy X-ray Reflectivity Study of Native Oxide Formed in Chemical Treatment

High-accuracy X-ray reflectivity measurements using synchrotron radiation have been carried out to study native oxides formed during various chemical-cleaning processes on Si wafer. Clear differences in the density of native oxides between various chemical treatments were obtained from the normalized reflectivity for the first time. Native oxides formed by HCl and NH4OH solutions have a low density, in contrast to the oxides formed by H2SO4 solution and UV/O3 whose densities are close to that of thermal oxide. These results are closely related to the results of chemical studies and the etching characterization of native oxides.

Nanoscale investigation of hydrogen-induced degradation mechanism in Pt/(Pb, La)(Zr, Ti)O3/Pt capacitors

The effects of hydrogen on Pt/(Pb, La)(Zr, Ti)O3(PLZT)/Pt capacitors have been investigated using atomic force microscopy piezoelectric measurements. The study revealed that the capacitors consist of submicron-sized ferroelectric domains, which were randomly distributed at positive or negative remanent states. After hydrogen annealing, it was observed that the local piezoelectric hysteresis loops of each domain shifted along both the voltage axis and the polarization axis. The degradation of remanent polarization can be explained by the shifted hysteresis of each domain. The degradation of saturation polarization can be understood to have been caused by the nonswitching portion within the capacitor.

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.

Identification of MOS Gate Dielectric Breakdown Spot Using High Selectivity Cl Radical Etching Technique

We have developed a simple method for identifying dielectric breakdown spots in gate oxides by using high selectivity Cl radical etching. This method is based on the phenomenon that Cl radicals do not penetrate SiO 2 . They can etch the Si substrate through the breakdown spot which acts as the etching path, namely, the current leakage path. During over-etching of the poly-Si gate electrode, a cavelike etched region in the Si substrate appeared under the breakdown spot of the gate oxide. This breakdown spot could be found by focusing the optics on the gate oxide located at a center on the etched region. We confirmed the local structure of the gate oxide which converted to crystallized Si due to intrinsic dielectric breakdown using transmission electron microscopy and energy dispersive x-ray spectroscopy. Cl radicals can etch the breakdown spot such as part of the crystallized Si in the gate oxide produced by intrinsic dielectric breakdown, and then etch a Si substrate under the breakdown spot.

High performance and highly reliable deep submicron CMOSFETs using nitrided-oxide

High performance and highly reliable CMOSFETs have been obtained using newly-developed nitrided-oxide processing, which features the localization of the nitrogen profile at the SiO/sub 2/-Si interface, and giving different nitrogen concentrations between the gate and LDD area. In p-MOSFETs, I/sub on/ can be increased by 12%, and I/sub off/ can be decreased by 50% compared with pure oxide. Also, in n-MOSFETs, hot carrier reliability significantly improves.

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.

INSTABILITY OF SIO2 FILM CAUSED BY FLUORINE AND CHLORINE INCLUSION

We studied how the interaction between fluorine and chlorine in SiO2 influences oxide thickness change and metal oxide semiconductor (MOS) reliability. Anhydrous HF treatment on amorphous Si (a-Si) introduces a large quantity of fluorine into the gate oxide compared to HF solution treatment. When the oxide is formed in an HCl atmosphere, it contains a large quantity of chlorine. If the fluorine atoms diffuse into the chlorine-rich oxide, Si–Cl bonds are easily replaced by Si–F bonds and the equivalent thickness increases. This tendency is further enhanced as the oxide becomes thinner. Both fluorine and chlorine, introduced in excess during the fabrication process, degrade MOS reliability because Si–F and Si–Cl bonds are weaker than Si–O bonds.