Ken Ninomiya

Reaction of atomic fluorine with silicon

The etch rate of Si with F atoms was measured by the use of F2 microwave plasma over a range of discharge pressures between 2.7×10−2 and 17 Pa. Fluorine atom concentration in the plasma was determined over the same pressure range by means of both gas‐phase titration and actinometry using Ar gas. A Si surface etched at 1.0×10−1, 5.3×10−1, 1.3, and 5.3 Pa was analyzed with XPS without exposing the surface to room air. A linear relation was obtained between the Si etch rate and the F atom concentration at discharge pressures between 2.7×10−2 and 2.7 Pa. The reaction probability of F atoms with Si to yield SiF4 was determined from the linear relation to be 0.1 for a Si surface at about 300 K. When the discharge pressure was higher than 1.3 Pa, the surface became rather strongly oxidized by O atoms resulting from residual gases. This surface oxidation results in a slight saturation of the Si etch rate at about 10 Pa.

Radio-frequency biased microwave plasma etching technique: a method to increase SiO2 etch rate

In order to increase the SiO2 etch rate in microwave plasma etching, a method of controlling the kinetic energy of ions impinging on a substrate surface covered with an insulator film was developed. In this method, radio‐frequency voltage is supplied to the substrate. A theoretical model and analysis for this method was made to define the substrate surface potential and the kinetic energy of impinging ions. Experimental verification of the analysis, and application of the method to SiO2 etching have been carried out. A SiO2 etch rate eSiO2 =40 nm/min, and selectivity to Si η2=eSiO2/eSi =4.0 were obtained with C3F8 etching gas and rf peak to peak voltage VBP=200 V.

Microwave plasma etching

Abstract A microwave plasma etching technique, which uses a microwave discharge with magnetic fields instead of a conventional rf discharge, has been developed. Submicron delineation with minimal surface damage and contamination can be performed with this technique. The motivation for developing the microwave plasma etching technique and the construction of the apparatus are described. Mechanisms for anisotropic and isotropic etching with this technique are discussed in terms of the experimentally obtained plasma parameters. A method for increasing the Si etch rate is presented in relation to the effects of surface covering films. These films can be detected by XPS measurements performed without exposing the etched surface to the atmosphere.

An experimental system for surface reaction studies in microwave plasma etching

An experimental system for studying surface reactions in the process of microwave plasma etching has been developed. In the system, a surface etched in the microwave plasma can be analyzed with x‐ray photoemission spectroscopy (XPS) without exposure of the surface to room air. In addition, we have developed a procedure for calculating a thickness of a surface layer stoichiometrically different from the substrate material and densities of atoms in the layer. Chemical changes in etched Si and SiO2 surfaces caused by exposing these surfaces to room air are investigated with XPS to show the utility of the system. When the surfaces etched in SF6 microwave plasma are exposed to room air, the chemical states of the surfaces change rapidly. This is mainly due to surface oxidation and adsorption of hydrocarbon compounds to the surfaces. The rapid changes are more clearly shown from increases in surface layer thickness and the number of O and C atoms in the layer. It is clarified that exposure of etched surface to ...

Role of sulfur atoms in microwave plasma etching of silicon

The Si etch rate in an (F2+O2) microwave plasma has been measured as a function of O2 mixing ratio at a fixed total pressure of 5.3×10−2 Pa. The etch rate significantly decreases with the mixing ratio. This etch rate decrease is due primarily to surface oxidation. When sulfur is added to the (F2+O2) plasma, the Si surface is much less oxidized and the etch rate increases by about a factor of 4. Such sulfur‐containing species as S atoms react with O atoms or ions in the plasma and form O atom‐containing species, such as SO2, SO+, SOF+, and SOF+2, thereby reducing the O atom and O+ ion concentrations in the plasma. As a result, the Si surface is scarcely oxidized, so that the etching reaction can easily proceed. Sulfur atoms inhibit surface oxidation and promote Si etching. Sulfur atoms contained in SF6, which is usually used in microwave plasma etching of Si, are expected to have the same role.

Activation energies of Si adsorbate diffusion on a Si(001) surface

Abstract The diffusion of Si adsorbates deposited on a Si(001) surface is studied by a reflection electron microscope (REM). The diffusion constants are obtained from the diffused lengths of the Si adsorbates. The activation energy of diffusion is determined with the Arrhenius plot of the diffusion constants. It is found that the activation energy on both 2 × 1 and 1 × 2 terraces changes at about 750°C. At temperatures below 750°C, the activation energy is about 1.4 eV, while it is about 2.7 eV at temperatures above 750°C. The change in activation energy is caused by the evaporation of the Si adsorbates from a Si(001) surface.

Fabrication of an axisymmetric Wolter type I mirror with a gold deposited reflecting surface

A small axisymmetric Wolter type I mirror was fabricated by a new film deposition method for an X-ray reflecting surface. In the film deposition, a gold (Au) electrode was inserted into a glass replica of the mirror. An Ar discharge was generated inside the replica at a discharge pressure of 44 Pa when a 40 kHz radio-frequency high voltage (-1.5–-3 kV) was supplied to the electrode. As a result of Au sputtering in the discharge, a 30 nm-thick Au film was deposited on the replica inner surface. The Au deposited surface had a surface roughness of 5–10 nm (peak to valley). A 300 µm-diameter X-ray beam with a reflectivity of 20% was obtained using a 6 mm-diameter MgKα X-ray (1253.6 eV) source. The present deposition method is suitable for producing metal deposited reflecting surfaces of axisymmetric X-ray mirrors.

Diagnostics of microwave plasma by laser induced fluorescence

CF radicals in a C3F8 microwave plasma were detected by laser induced fluorescence (LIF). CF2 radicals in C3F8 and CF4 plasma were also observed by using the same technique. At discharge pressures of 0.13 and 4.0 Pa, the relative densities of both radicals were measured as a function of microwave input power over a range of 40–240 W. The dependencies of these radical densities on discharge pressure were also measured over a pressure range of 6.7×10−2 to 13 Pa. The reaction mechanism in the plasma is discussed in terms of experimental results.CF radicals in a C3F8 microwave plasma were detected by laser induced fluorescence (LIF). CF2 radicals in C3F8 and CF4 plasma were also observed by using the same technique. At discharge pressures of 0.13 and 4.0 Pa, the relative densities of both radicals were measured as a function of microwave input power over a range of 40–240 W. The dependencies of these radical densities on discharge pressure were also measured over a pressure range of 6.7×10−2 to 13 Pa. The reaction mechanism in the plasma is discussed in terms of experimental results.

Si Etching with a Hot SF6 Beam and the Etching Mechanism

Silicon surface etching using a hot SF6 (SF6*) molecular beam is being investigated in the interest of studying the influence of vibrational energy on surface reactions and developing a damage-free etching technique. The SF6* beam is produced by the free jet expansion of SF6 gas heated in a quartz furnace. It is seen that SF6* vibrational energy enhances the Si etch rate. It is also shown that the Arrhenius model modified to take the vibrational energy effect into account can explain the experimental results. The model parameters are then determined to be 6500 cm-1 for activation energy (Ea), 0.17 for the efficiency (α) of the vibrational energy used to clear the activation energy barrier, and 5.0 for the frequency factor (A).

Titration Method for Measuring Fluorine Atom Concentration in Microwave Plasma Etching

A titration method has seen developed to measure the concentration of fluorine (F) atom in microwave plasma etching. A rapid reaction of F atoms with H2 gas is used as a titration reaction to determine the absolute F atom concentration. Applying the present method to SF6 microwave discharge, the F atom concentration is measured under various discharge conditions. The F atom concentration is 2.9-4.0×1011 cm-3 at a typical operating pressure of 6.7×10-2 Pa and a microwave power of 200 W. It is confirmed that relative changes in the concentration agree well with those obtained with the optical spectroscopic method.