Yoko Ueda

Role of extraordinary waves in uniform electron cyclotron resonance plasmas

The extraordinary wave (X wave) was found to contribute to the uniformity of an electron cyclotron resonance (ECR) plasma whose electron density is about 1–2×1017 m−3. The X wave propagated radially in the plasma both before and after the ECR point. The electron density jump occurred when the electron density was equal to the cutoff density of the X wave at the ECR point. Upon increasing the electron density, only the whistler wave propagated in a high density plasma of about 1018 m−3.

Role of peripheral vacuum regions in the control of the electron cyclotron resonance plasma uniformity

Spatial measurements of the ion saturation current density indicate stable vacuum regions in a periphery of electron cyclotron resonance (ECR) plasma. The vacuum regions have a possibility to contribute to plasma uniformity by behaving as a waveguide for the incident electromagnetic waves. Mode conversion of electromagnetic waves with long wavelength to the right circular polarized wave was observed experimentally at a certain radial position. Furthermore, microwave propagation in a partially filled plasma chamber was examined numerically. The simulation indicated that the electromagnetic waves with long wavelengths propagated in a periphery of the plasma were converted into the extraordinary wave or electrostatic waves outside the ECR region and that the power absorption took place at the local regions. Physical considerations toward these results imply the reason why the plasma uniformity is influenced by magnetic field gradient.

Plasma parameter measurements and deposition of a-Si:H thin films in pulsed ECR plasma.

Abstract Pulse modulation of the incident microwave power was investigated for the control of plasma parameters and improvement of the films deposited in ECR plasma. Measurements of the temporal variation of plasma parameters in the pulse-modulated ECR plasma indicate that the electron density varies little in time while the electron temperature decreases rapidly within 10 μs after the discharge. The results suggest that pulse modulation where the power-off period is approximately 10 μs enables reduction of the mean electron temperature while keeping a high electron density. Furthermore, we have prepared hydrogenated amorphous silicon films by the ECR plasma CVD method. It was found that the ratio of photoconductivity to dark conductivity of the film was improved from 103 to 2.5×105 without heating the substrate and the deposition rate was 14 A/s by pulse-modulated ECR plasma.

EFFECT OF UPPER HYBRID WAVES ON UNIFORM ELECTRON CYCLOTRON RESONANCE PLASMAS

The extraordinary wave (X wave) was found to contribute to the uniformity of an electron cyclotron resonance (ECR) plasma whose electron density is about 1–2×1011 cm−3. The X wave propagated radially in the plasma both before and after an ECR point. The wavelength of the X wave changed radially according to the local electron density. The experimental results indicated a possibility that an upper hybrid resonance (UHR) sustained the very uniform ECR plasma. With increasing input microwave power, the radial profile of the ion saturation current density changed from uniform to convex abruptly, and the electron density at a center increased to about 1012 cm−3 with an electron density jump. Only the whistler wave propagated axially in the high density plasma of about 1012 cm−3. It was found, by measuring electromagnetic waves, that the radial profile of the ion saturation current density abruptly changed when the electron density was nearly equal to the cutoff density of the X wave at the ECR point.

Measurement of ion temperatures in a large-diameter electron cyclotron resonance plasma

The ion temperature in a large-diameter electron cyclotron resonance plasma is measured using high-resolution optical emission spectroscopy, and the correlation between the ion temperature and fluctuations observed near the chamber wall is investigated. Furthermore, the effect of multicusped fields on the ion temperature is examined. The ion temperature and the amplitude of ion saturation current fluctuations are found to decrease when multicusped fields are applied. The ion temperature and fluctuations increase with increasing incident microwave powers from 2.0 to 2.5 kW, indicating that the ion temperature is correlated with the fluctuation amplitude. The measurement of the ion saturation current fluctuation and floating potential fluctuation suggests that the fluctuations are excited by flute instability.

Production of low electron temperature ECR plasma for thin film deposition

Abstract An electron cyclotron resonance (ECR) plasma with low electron temperature parallel to the magnetic field was produced by applying the mirror magnetic field for Ar, Ar/N 2 and H 2 gasses. It was found that the temperature parallel to the magnetic field was lower than the temperature perpendicular to the field by 5∼50% and decreased at the ‘throat’ of the mirror magnetic field. Especially, the electron temperature parallel to the magnetic field was observed to be less than 2 eV in the Ar/N 2 and the H 2 plasma. Our experimental results suggested that the high-quality thin films could be prepared by setting the substrate perpendicular to the field lines at the ‘throat’ of mirror magnetic field because of the decrease in ion bombardment to the substrate.

Production of a large diameter electron cyclotron resonance plasma using a multislot antenna for plasma application

An electron cyclotron resonance plasma with large diameter, uniform, and high electron density is produced using a multislot antenna. The uniformity of the plasma is within 5% over 20 cm in diameter. The electron density of the helium plasma in front of a substrate is 7×1010 cm−3, while the electron density without the substrate is higher than the cutoff density for 2.45 GHz. The effect of the magnetic field configuration on plasma uniformity is investigated. Both of the R wave (electron cyclotron wave) and L wave are found to be excited in the plasma.

Production of Low-Electron-Temperature Electron Cyclotron Resonance Plasma Using Nitrogen Gas in the Mirror Magnetic Field

An electron cyclotron resonance (ECR) plasma with a low electron temperature (< 2 eV) and high electron density (~1012 cm-3) was realized in a mirror magnetic field for Ar/N2 or N2 gas. It was found based on the particle and power balance that the decrease in the electron temperature was due to the magnetic-mirror confinement depending on the collision cross section between electrons and neutral particles. The experimental and numerical results suggest that diluting with N2 gas, whose excitation cross section peaks at a low electron energy of about 2 eV, in the mirror magnetic field enables us to reduce the electron temperature efficiently in an ECR plasma.

Deposition of large area amorphous silicon films by ECR plasma CVD

Abstract The deposition of hydrogenated amorphous silicon (a-Si:H) films over a large area were performed using an electron cyclotron resonance (ECR) plasma with a multi-slot antenna. The uniformity of the ECR plasma was within 5% over 200 mm in diameter, and the density and temperature of electrons in front of a substrate were 7 × 10 16 m −3 and 6 eV, respectively. Hydrogenated amorphous silicon films were deposited from flowing SiH 4 (10%) He gas. The deposited films were almost 200 mm in diameter, corresponding to that of the plasma. The deposition rate, optical band gap, and infrared (IR) absorption of the films were investigated to find whether the multi-slot antenna was effective for chemical vapor deposition (CVD); as the substrate temperature was increased, the optical band gap decreased.

Investigation of ECR plasma uniformity from the point of view of production and confinement

Abstract To clarify the production mechanism of a high-density uniform electron cyclotron resonance (ECR) plasma, the spatial wave patterns of electromagnetic waves in the plasma were measured by the interferometric method under several experimental conditions and compared with the power absorption profiles indicated by simulation. It was experimentally shown that the refraction of the right circularly polarized wave (the R wave) corresponds to the spatial profile of the plasma density. On the other hand, the simulation showed the correlation between the wave refraction and power absorption, which implies that the power transportation depending upon the refraction of the R wave has a great influence on ECR plasma uniformity. Furthermore, it was found that the plasma uniformity was improved by applying permanent magnets, and the maximum electron density in the case of the uniform plasma is approximately 2×1011 cm−3. The ion temperature in the Ar plasma decreases from 0.17 to 0.06 eV in the presence of the permanent magnets.