Kenji Maeda

Frequency modulation response of a liquid-crystal electro-optic device doped with nanoparticles

Palladium nanoparticles covered with liquid-crystal molecules were prepared by UV irradiation of an alcohol solution of palladium(II) acetate in the presence of liquid-crystal molecules. The prepared Pd nanoparticles have an average diameter of 2.5 nm. A twisted nematic (TN) liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of nematic liquid-crystal molecules. In this device the sign of the dielectric anisotropy (Δe) of the liquid-crystal molecules, which cover Pd nanoparticles, is opposite to that of nematic liquid-crystal molecules, which work as the host of the device (Δe>0). The TN-LCD cell fabricated in this research exhibits a frequency modulation response to an applied alternative voltage wave form.

Frequency modulation response of a tunable birefringent mode nematic liquid crystal electrooptic device fabricated by doping nanoparticles of Pd covered with liquid-crystal molecules

We fabricated a tunable birefringent (TB) mode nematic liquid-crystal (NLC) electrooptic device using NLC-K15 (Merck) as a host NLC (called NLC-1), where the cell is doped with Pd nanoparticles covered with NLC (NLC-2) molecules, having a cyano group such as 5CB (Merck) with positive dielectric anisotropy (Δe>0) or CCN-47 (Merck) with negative Δe (Δe<0). The diameter of the core Pd particle is 2.5 nm and the concentration of nanoparticles is 1 wt%. The TB mode LCD cell fabricated in this way exhibits a remarkable frequency modulation response below 100 Hz of the driving voltage waveform. It is considered that the frequency modulation (FM) response of the TB-NLCD may be attributed to Maxwell-Wagner type interfacial polarization between the host NLC medium and doped nanoparticles.

Real Time Estimation and Control of Oxide-Etch Rate Distribution Using Plasma Emission Distribution Measurements

We studied real-time estimation and automatic control of etch-rate distribution in order to develop next-generation oxide etching techniques that will have improved reliability and reproducibility when used in mass production processes. We specifically investigated the relationship between plasma emission intensity (PEI) distribution detected by silicon photodiodes and oxide etch-rate distribution. We found that there was a strong correlation (correlation coefficient = 0.988) between the uniformity of oxide etch-rate distribution and relative PEI distribution. We also found that relative changes in oxide etch-rate uniformity of ±1% can be detected in real time by measuring PEI distribution. We then demonstrated that self-adjustments of oxide etch-rate distribution are possible by using feedback based on the monitoring PEI distribution to control magnetic field conditions. Moreover, we demonstrated that monitoring PEI distribution can be used to observe fast phenomena that occur in the order of milliseconds during the plasma transition process. These phenomena are related to charging damage, such as plasma ignition and disappearance.

Study on the Distribution Control of Etching Rate and Critical Dimensions in Microwave Electron Cyclotron Resonance Plasmas for the Next Generation 450 mm Wafer Processing

A newly designed microwave electron cyclotron resonance (ECR) plasma etching reactor has been developed for 450 mm wafer processing. The etching rates of polycrystalline silicon (poly-Si) and SiO2 across the wafer were evaluated as a function of ECR position. Two-dimensional (radial and vertical) distributions of the ion flux in the reactor were also investigated using a movable single probe system. A ring-shaped region of high-density plasma along the ECR plane was observed. This reveals the mechanism that the etching-rate distribution could be controlled by the ECR position. As a result, a polycrystalline silicon etching rate uniformity of 1.5% across a wafer was successfully obtained. Furthermore, the uniformity control of critical dimensions (CDs) based on wafer temperature was also investigated, and CD uniformity below 3 nm across the wafer was obtained in the optimum temperature distribution.