Tetsu Mieno

Pulse-time modulated plasma discharge for highly selective, highly anisotropic and charge-free etching

Highly selective, highly anisotropic, notch-free and charge-build-up damage-free polycrystalline silicon etching is performed by using electron cyclotron resonance plasma modulated at a pulse timing of a few tens of microseconds. A large quantity of negative ions is produced in the afterglow of the pulse-time modulated plasma. The decay times of electron density, electron temperature and sheath potential are considerably reduced, which is attributable to negative ion generation. Furthermore, the pulse-time modulated plasma reduces the time-averaged sheath potential. As a result of these effects, charged particles in the sheath are strongly modified from the continuous discharge, and they should improve selective etching in the pulsed ECR plasma and elimination of charge accumulation on the substrate.

Pulse–time‐modulated electron cyclotron resonance plasma discharge for highly selective, highly anisotropic, and charge‐free etching

Highly selective, highly anisotropic, notch‐free, and charge‐buildup damage‐free silicon etching is performed using electron cyclotron resonance (ECR) Cl2 plasma modulated at a pulse timing of a few tens of microseconds. A large quantity of negative ions are produced in the afterglow of the pulse‐time‐modulated plasma. The decay times of electron density, electron temperature, and sheath potential are considerably reduced. This is attributable to negative‐ion generation. Furthermore, the pulse‐time‐modulated plasma reduces the time averaged sheath potential. As a result of these effects, charged particles in the sheath are drastically modified from the continuous discharge, and they should improve the selective etching in the pulsed ECR plasma and eliminate charge accumulation on the substrate. Additionally, negative‐ion generation dramatically improves the plasma potential distributions in the nonuniform ECR plasma. This technique is also suitable for large scaled etching processes.

Production and control of K–C60 plasma for material processing

An ultrafine‐particle plasma including large negative fullerene ions is produced by introducing fullerene particles into a low‐temperature (≊0.2 eV) potassium plasma column confined by a strong axial magnetic field. The density ratio of the negative fullerene to positive potassium ions is controlled by changing the oven temperature for fullerene sublimation and the plasma density being varied in the range from 0 to 0.97 in the central region of the plasma cross section. Since the electrons are well confined in the central region, the ratio increases radially and is more than 0.9999 in the radial edge region. A thin film consisting of the potassium and fullerene particles is formed on a metal end plate which terminates the plasma column. Depending on the end plate potential and radial position, the film is verified to contain metal‐doped fullerenes with the potassium atom in the endohedral cavity, which are formed as a result of the potassium‐atom insertion into the stable cage of fullerene particles.

Effect of oxygen on electric conductivities of C60 and higher fullerene thin films

Abstract The dark conductivities and photoconductivities of C60 and higher fullerene (C70, C76, C78 and C84) thin films in oxygen gas at room temperature have been investigated. It was found that the time dependences of both the dark conductivities and photoconductivities of higher fullerene films are of the same pattern as those of a C60 film in oxygen gas. These electric conductivities quickly decrease after the films are exposed to oxygen gas or air. Both the dark and photoconductivities of C60 and C70 films are much higher than those of higher fullerene (C76, C78 and C84) films in vacuum. However, the dark conductivities of these fullerene films after 24-h treatment in oxygen gas become of the same order of magnitude. The degree of reduction and saturation times of the electric conductivities of higher fullerene films in oxygen gas are smaller and longer, respectively, than those of C60 and C70 films.

Generation and extinction characteristics of negative ions in pulse-time-modulated electron cyclotron resonance chlorine plasma

The time dependence of plasma parameters in a pulse-time-modulated electron cyclotron resonance plasma of and Ar source gases is measured. It is found that plasma produces a large quantity of negative ions during afterglow and decay times of electron density, electron temperature and sheath potential of plasma are much smaller than those of Ar plasma. The negative ions in plasma stay for a long time in the afterglow and they quickly become extinct when the microwave power is turned on. These characteristics suggest that the pulse modulation of plasma produces a large amount of negative ions and changes the flow of charged particles through the sheath region to the substrate surface, which enables us to improve highly anisotropic and charge-free poly-Si etching.

Stationary Double Layers in a Collisionless Magnetoplasma

Stationary double layers are generated in a magnetoplasma by applying potential differences between two heated plates on which the plasma is produced by surface ionization. Their potential drop φ D is varied over a wide range e φ D / T e ≃1-2×10 3 ( T e : electron temperature in eV) without any influence from volume ionization of the background gas. There are always spiky fluctuations especially on the low-potential tail of the double layer. By measuring the double-layer formation process, a localized potential drop is found to be formed initially in front of the plate on the low-potential side, being accompanied with current limitation. This localized potential drop moves along the plasma column, but finally stops and results in the formation of the stationary double layer in the presence of sufficient plasma supply from the plate on the high-potential side.

Effects of Gravity and Magnetic Field in Production of C60 by a DC Arc Discharge

We have examined the dependence of the production of C60 on the direction of the arc current with respect to the direction of gravity in a DC arc discharge in a helium gas atmosphere. The production rate decreases when the direction of the current is opposite to that of heat convection of the helium gas. When a DC magnetic field is applied, the hot gas plasma in the arc region is jetted out by the J×B force. The production rates of carbon soot and C60 increase and depend little on the direction of gravity.

Efficient production of O+ and O− ions in a helicon wave oxygen discharge

High density oxygen plasmas (ne=1010–1013 cm−3) are produced by a helicon wave discharge source with rf powers of 0.1–3 kW. Positive and negative ion species in the plasmas are measured by a time‐of‐flight mass spectrometer. The intensity ratio of O+ to O+2 increases with the electron density ne and is almost proportional to it in the region of ne=1010–1012 cm−3. When the electron density increases up to 8×1012 cm−3, the ratio becomes about 4. In a high density plasma of 1.3×1013 cm−3 obtained by mixing Ar gas, about 83% of the positive oxygen ions becomes O+. By using pulse modulation of the rf power, O− ions are mainly observed with remarkable increase in the afterglow. The maximum density of O− is about 3×1011 cm−3 at 30 μs after turning off the rf power of 0.85 kW and the decay time of O− is about 60 μs.

Conductive cotton textile from safely functionalized carbon nanotubes

Electroconductive cotton textile has been prepared by a simple dipping-drying coating technique using safely functionalized multiwalled carbon nanotubes (f-MWCNTs). Owing to the surface functional groups, the f-MWCNTs become strongly attached with the cotton fibers forming network armors on their surfaces. As a result, the textile exhibits enhanced electrical properties with improved thermal conductivity and therefore is demonstrated as a flexible electrothermal heating element. The fabricated f-MWCNTs/cotton textile can be heated uniformly from room temperature to ca. 100°C within few minutes depending on the applied voltage. The textile shows good thermal stability and repeatability during a long-term heating test.

Time variation of plasma properties in a pulse-time-modulated electron cyclotron resonance discharge of chlorine gas

Time dependence of plasma parameters in a pulse-time-modulated electron cyclotron resonance plasma of Cl2 and Ar gases is measured. It is found that Cl2 plasma produces a large quantity of negative ions during afterglow and that decay times of electron density, electron temperature and sheath potential of Cl2 plasma are much smaller than those of Ar plasma. The results suggest that the pulse modulation of Cl2 plasma changes the flow of charged particles through the sheath region to the substrate surface and enables us to improve highly selective and charge-free poly-Si patterning.