Hiroshi Muta

Thomson scattering measurements of electron temperature and density in an electron cyclotron resonance plasma

Electron temperature Te and density ne in the source region of an electron cyclotron resonance discharge have been measured by incoherent Thomson scattering of the beam from a 0.5 J yttrium aluminum garnet laser. This is the first experiment in which this technique, routinely used on fusion plasmas, has been applied to a processing plasma. Measurements were made in an argon discharge at pressures from 0.3 to 2 mTorr and microwave powers from 250 to 1000 W. Velocity distributions were measured both parallel and perpendicular to the magnetic field and a slight anisotropy of electron temperature was observed for low‐pressure discharges. Temperatures in the range of 1–5 eV and densities in the range of 2–10×1017 m−3 were measured. Te and ne were found to strongly depend on pressure but only weakly on the input power and discharge magnetic field. No deviations from a Maxwellian velocity distribution were observed.

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.

Spatial distributions of electron temperature and density in electron cyclotron resonance discharges

Spatial profiles of electron density and temperature of electron cyclotron resonance discharge plasmas have been successfully measured using laser Thomson scattering. The results, thus obtained, were valuable for quantitative comparison with results of a computer simulation. Measurements were performed for two cases with different locations of the electron cyclotron resonance zones. Simulation results obtained from a hybrid code, which treats ions and neutral particles as discrete particles and electrons as a fluid, were fitted to the experimental profiles of the electron density and temperature by adjusting the microwave power deposition profiles. From these comparisons and an analysis of other simulation data, it was found that the large difference of radial electron density profiles for two discharge conditions was caused by the difference of radial space-charge electric-field distributions. The radial electron temperature distribution determined the radial electric field that drove the ions radially a...

Numerical investigation of a low-electron-temperature ECR plasma in Ar/N2 mixtures

In general, electron temperature is an important plasma parameter which has much influence in the film property. In this paper, the mechanism for decreasing the electron temperature in an electron cyclotron resonance plasma is numerically investigated using a fluid model. A mixture of argon and nitrogen is used as the working gas under the assumption of plasma nitridation. The simulation was carried out with typical magnetic field configurations and various mixture ratios. As a result, it was found that the application of magnetic mirror was suitable for the production of a low-electron-temperature plasma. Besides, the calculation results indicated that the addition of nitrogen was effective to decrease the electron temperature approximately 2 eV due to the vibrational excitation of nitrogen molecules by electron impact.

Numerical investigation of the production mechanism of a low-temperature electron cyclotron resonance plasma

The mechanism to decrease the electron temperature in an electron cyclotron resonance (ECR) plasma was numerically investigated using a fluid model. A mixture of argon and nitrogen was used as the working gas under the assumption of plasma nitriding by reactive sputtering. It was found that the power loss due to the vibrational excitation of nitrogen molecules by electron impact contributed to the decrease of electron temperature and the effect was promoted by the application of a mirror-type magnetic field configuration.

Study of the effect of a probe on the plasma in the source region of an electron cyclotron resonance discharge

Langmuir probes are commonly used to measure electron density and temperature in the low temperature and low density plasmas used in plasma processing, although the plasma conditions are sometimes not ideal for such measurements. We report measurements of the perturbing effect of such probes in the high magnetic field region of an electron cyclotron resonance discharge by making Thomson scattering measurements of electron temperature and density under normal operating conditions and also in the presence of a probe. The results revealed that the probe clearly qualitatively changed the plasma. An attempt to quantify this change appeared to indicate that the effect of the probe was to decrease the electron density and increase the electron temperature in the vicinity of the probe.

Effect of Excitation Frequency on the Spatial Distributions of a Surface Wave Plasma

Using different frequencies of 2.45 GHz and 915 MHz, the effect of excitation frequency on the spatial distributions of a surface wave plasma for 450 mm wafer processing was experimentally investigated at a medium pressure of 1 Torr. As a result, it was found that the mode number of standing waves which the surface waves form in the radial direction has great influence on the radial distribution of plasma density. Consequently, the plasma uniformity in the downstream region at 915 MHz was better than that at 2.45 GHz. On the other hand, the electron temperature was roughly constant and below 1.5 eV except in the vicinity of the quartz window at both frequencies.

Generation of a low-electron-temperature ECR plasma using mirror magnetic field

The mechanism to generate a low-electron-temperature electron cyclotron resonance plasma using magnetic filed and mixture ratio was investigated by means of simulation and experiment. As the working gas, a mixture of argon and nitrogen was used under the assumption of plasma nitriding. The results showed that the application of the magnetic mirror was valid for decreasing the electron temperature due to both effects of plasma confinement and temperature anisotropy. Furthermore, the addition of nitrogen was found to be effective to decrease the electron temperature approximately 2 eV due to the vibrational excitation of nitrogen molecules by electron impact.

Effect of electromagnetic waves propagating in the periphery of electron cyclotron resonance plasma on the uniformity

Stable vacuum regions in the periphery of an electron cyclotron resonance (ECR) plasma near a quartz window were found to possibly contribute to plasma uniformity as a kind of a waveguide for incident electromagnetic waves. Mode conversion of electromagnetic waves with long wavelength into the right circularly polarized wave was observed clearly at a certain radial position. In order to investigate the effects of electromagnetic waves propagating in the vacuum region on plasma production or uniformity, microwave propagation in a partially filled plasma chamber was examined numerically. The numerical results indicated that the electromagnetic waves with long wavelengths in the periphery of the plasma were converted into extraordinary or electrostatic waves outside the ECR region and that power absorption took place locally. Furthermore, it was found to be strongly dependent on the width and shape of the vacuum region and gas pressure. Physical considerations of these results revealed the reason why plasma uniformity is influenced by a magnetic field gradient.

Development of a hybrid PIG-ECR ion source

AbstractA combined ion source with 20 cm beam diameter, utilizing both a cold-cathode Philips or Penning ionization gauge (PIG )discharge and an electron cyclotron resonance (ECR ) discharge, has been built and tested. The ion source has been designed tostudy what effects, if any, might be induced by superimposing microwave power at the ECR condition onto a cold-cathode PIGion source at low pressures (F10 Torr y4 ). The first experiments with argon gas indicate that the ECR coupling at low pressuresresults in: (a) transformation of the PIG discharge mode with a dominant anode fall into the hybrid discharge mode with adominant cathode fall; (b) stabilization of the PIG discharge; and (c) enhanced ion beam output due to increased ionizationinside the ion source. The ion beam current is 150 mA (with a beam current density at its axis of 0.35 mA ycm 2 ), at an anodevoltage of 750 V, a microwave power of 200 W and a gas pressure of 0.05 mTorr. The ion source design and the results ofpreliminary experiments are presented. A stable low-pressure operation mode of the ion source might be promising for broad ionbeam production. 2003 Elsevier Science B.V. All rights reserved.