Katsumi Yoneda

Carbon-Doped Silicon Oxide Films with Hydrocarbon Network Bonds for Low-k Dielectrics: Theoretical Investigations

We have computationally explored the chemical structures of carbon-doped silicon oxide (SiOCH) films that give the smallest dielectric constant (k) under the required mechanical strength for low-k dielectrics. The focus of this study is on the SiOCH structures that have hydrocarbon components in the polymer network as cross-links. It has been found that SiOCH films of small dielectric constants can have improved mechanical strengths if the hydrocarbon components form cross-links, instead of the terminal methyl groups in the conventional structure. The calculated results suggest that SiOCH films of ideal structures can have substantially smaller dielectric constants than films of current interconnect technology with the same mechanical strengths.

Ultraviolet-Curing Mechanism of Porous-SiOC

Utilizing the structure of porous SiOC determined in our previous study, we investigated a mechanism for improving the properties of porous SiOC film by ultraviolet irradiation (UV curing). The generation of a Si–O–Si cross link from an OH group and its adjacent CH3 group is the primary process in UV curing. This cross-link generation enhances mechanical strength of the material and lowers the dielectric constant. Decrease in the number of CH3 groups and increase in the number of Si–H bonds, both due to UV curing, cause slight increases in mass density and dielectric constant of the film.

Vacuum lithography—A completely dry lithography using plasma processing

The purpose of this paper is to describe a thoroughly dry lithography using plasma polymerization and plasma etching. The new lithography is named vacuum lithography because all processes are performed at reduced pressures. Resist films were formed in bell-jar-type and argon-flow-type reactors. The controllability of plasma polymerization is discussed with respect to the type of reactor and gas mixture. A pattern was delineated in the resist using an electron beam, and it was developed by plasma etching with a mixture of argon and oxygen. It was found that the quality of the plasma-polymerized resist depends strongly on the polymer structure and on the plasma etching conditions. In this experiment, the recorded values of sensitivity and γ value of plasma-polymerized methyl methacrylate were 700 µC/cm2 and 1, respectively.

Vacuum lithography using plasma polymerization and plasma development

Abstract A completely dry lithography has been proposed which involves plasma polymerization of methyl methacrylate (MMA) and plasma development with CCl 4 . It was called vacuum lithography because all processes were performed in a vacuum. However, the developed pattern had a lower resolution than patterns produced by conventional lithography with a wet process. After several technical refinements, the quality of the resist and the developed pattern was markedly improved. In this paper, recent results will be reported. A gas-flow-type reactor was used instead of a bell-jar-type reactor because the morphology of plasma-polymerized MMA (PPMMA) varied with each experimental run which was performed with the same gas and discharge parameters. The monomer vapour was introduced downstream of the argon discharge, and the polymerized film was formed on the substrate placed further downstream in the mixed gas. The development of pattern was performed by etching with an Ar-O 2 mixture and with hydrogen gas instead of CCl 4 gas, because the etching rate of the resist was too high in a CCl 4 plasma and a clear pattern was not obtained. The evaluated sensitivity and γ value of PPMMA were 1000 μC cm −2 and 1 respectively. MMA containing 5% tetramethyltin was also used as a monomer gas for plasma polymerization downstream of the argon discharge. In this case the sensitivity and γ value were 10 μC cm −2 and 2 respectively.

Novel plasma polymerization system using a d.c. glow discharge

Abstract Plasma polymerization using a direct current (d.c.) glow discharge was carried out using several organic compounds. We have developed a plasma-polymerization instrument capable of using not only gaseous monomers but also liquids and solids as the starting materials. The characteristics of films prepared by d.c. glow discharge were examined by Fourier transform infrared spectroscopy and Raman spectroscopies, electron spectroscopy for chemical analysis, and contact angle measurements. The chemical structures of the deposited films were greatly influenced by the applied d.c. voltages during the discharge. Hydrogen-free carbon films were prepared from plasma polymerization of both naphthalene and benzene; the structure of these films, evaluated by Raman spectra, were quite different. Comparison of films deposited in different regions of the plasma, such as in the negative glow-phase region and in the positive column region, were performed. From these experiments similar film compositions were obtained.

Double Twin Path Interferometer for Thin Film Thickness Measurement

A unique interferometer which can automatically measure the thickness of a film with a simultaneous reference level control is described. This is achieved by using a grating to split a laser beam into various orders. The interference between the diffracted components of the 0 and -1 orders is used to control the reference level and the interference between the diffracted components of there two orders gives a measurement of the film thickness. Theoretical calculations show a very good linearity and high precision. Aluminium films with thicknesses ranging from 700 to 3000 A were measured with a precision of ±200 A. Remedies for an improvement of the precision are discussed.

Tilt-insensitive film thickness measurement using a double twin-path interferometer

Abstract A lock-in amplifier detection method for measuring the film thickness on a flat substrate has been developed by using a common-path interferometer. The signal due to the film thickness has been obtained without it being affected by the tilting of the substrate. The sensitivity was better than 0.5 nm.

Measurement of SAW Propagation Properties Using a Laser Probe

Measurements of surface acoustic waves (SAW) propagation properties such as amplitude profiles and phase and group velocities on LiNbO3 have been done using a very stable and highly sensitive laser probe which is a type two-beam interferometer with minimum detectable SAW amplitude 8×10-3 A at 56 MHz on 127.86° rotating Y-cut LiNbO3. Amplitude profiles are measured for two types of interdigital transducers (IDT) with ten parallel finger pairs and ten circular-arc finger pairs. Results of phase velocity measurements are shown on a table and compared with the literature1) for certain orientations of LiNbO3 or LiTaO3.

Measurement of liquid surface properties using a He-Ne laser

Abstract The surface tension, viscosity, and damping coefficient of surface waves on a liquid sample have been determined by observing the diffraction of an optical beam. To achieve high accuracy, a He-Ne laser having a high brightness and coherence was used as a light source. Experiments illustrating and verifying the techniques are described. Values of the surface tension for different samples have been measured with a standard deviation of less than ±0.6% for frequencies of the ripple motion ranging from 500 to 3 000 Hz over the temperature range 20–45°C. The viscosity and damping coefficient of water were measured for frequencies in the range 600–1500 Hz. The values obtained agree with those available from the literature.