Shosaku Matsumura

Diagnostics of an inductively coupled CF4/Ar plasma

Experimental data for radiative and metastable state densities in pure argon and in mixture of 5% CF4 in argon are obtained to study the effect of CF4 on kinetics of inductively coupled plasma (ICP). The measurements were made by a combination of optical emission spectroscopy and computer tomography for radiative levels and by laser absorption for metastable state profiles. The data were obtained in an inductively coupled rf (13.56 MHz) plasma with a single coil and full cylindrical symmetry. At low pressures of 5 and 15 mTorr the data in pure argon and in the mixture do not differ much, both in the magnitude and in the radial and axial profiles. However, at 50, 100, and 300 mTorr there is a dramatic change when CF4 is introduced. The metastable density increases due to the smaller electron induced quenching while axial and radial profiles are quite different. Unfortunately introduction of CF4 spoils the degree of azimuthal isotropy. The observed results and explanations based on the important role of met...

Negative Ion Density Determination Using Probe to Detect Photo-Detached Electron by Continuous Wave Laser

Theoretical calculation of probe current increase caused by photo-detachment of electrons by laser irradiation in a plasma and experimental studies have been done in order to determine the absolute negative ion density. The positive column of a hollow cathode DC Ar:O 2 discharge is used in the experiment. During laser irradiation of the anode, detected photo-detached electron current increases with increase of the laser on-off frequency because of temporal space potential change. The O - densities determined from the theoretical calculation show good agreement with those theoretically predicted based on Ichikawas theory when the laser does not irradiate the anode.

Time-Resolved Measurements of RF Plasmas Using Electrostatic Probe Having Compensation Circuits for Space Potential Fluctuation

The time-resolved Langmuir probe method using a laser-heated emissive probe to compensate space potential fluctuation is modified to improve the limit of amplitude for compensation and reliability of current detection in order to experimentally study RF plasma under various conditions. Time-resolved electron temperatures and electron densities are measured at various input powers and pressures of Ar and He in 13.56 MHz RF asymmetric discharge. Not only the electron temperature but also the electron density change was synchronized with excitation RF. The period of variation is not the same as second harmonics, but is a fundamental period of 13.56 MHz. The electron temperature and the self-bias depend on the excitation RF power. Such evidence may indicate that plasma parameters are closely related with the electron acceleration in the electrode sheath and the plasma caused by the self-bias field.

Measurement of Negative Ions Using Improved Probe for Detection of Photodetached Electrons.

Negative ion measurement applying an electrostatic probe to detect photodetached electrons in noisy plasma has been performed using a compensation circuit with an additional probe. The detected photodetachment current is dependent on the probe surface material. A carbon-coated probe yields the best results in reproducibility and sensitivity in our experiments. The time response of photodetached electron current caused by laser irradiation has also been monitored. The transient current is two to three orders of magnitude larger than the steadystate current at the instant the laser is turned on. Therefore, the absolute determination of steadystate photodetachment current using laser light chopping and the lock-in amplifier is unreliable.

Self-compensated standing wave probe for characterization of radio-frequency plasmas

A simple self-compensated Langmuir probe using the character of a standing wave is developed for characterization of radio-frequency (RF) discharge plasmas. This probe is based on a concept that the interference of RF field is eliminated at the node of a standing wave which exists ideally at one-fourth of the RF wavelength (λ/4) away from the probe tip in the plasma. The fluctuation of plasma space potential is suppressed as confirmed by comparison with a non-compensated probe and a self-compensated probe using an inductor-capacitor (LC) resonant circuit. The plasma parameters obtained with the standing wave probe are in agreement with those with the LC resonant probe within discrepancy of 15% indicating high reliability of the results.

Modelling of noble gas-SiH4 gas mixture glow discharge positive column plasmas

Numerical modelling of He-SiH 4 , Ne-SiH 4 and Ar-SiH 4 gas mixture glow discharge positive column plasmas is conducted for the gas pressure from 0.1 to 30 Torr, the percentage silane gas mixture in a noble gas from 0.01 to 10%, and the electron density from 10 9 to 10 13 cm -3 . The results show that the plasma parameters significantly depend on the combination of the choice of the noble gas and the silane mixture fraction

Digitalized triple‐probe system for the direct display of electron temperature in a time‐varying plasma

A technique for instantaneous linear digitalization of plasma electron temperature display using a triple‐probe method is presented. A digitalized feedback is introduced between the floating probe voltage and the voltage applied to the other probes which is proportional to the electron temperature. Transfer of digitalized data by a photocoupler is used to suppress the side current which causes serious error on a triple‐probe method. The results show that the measured electron temperatures are in a fairly good agreement with a Langmuir single‐probe data. Present system can be applied to most of a low‐density plasma when the ratio (probe radius/Debye length) is less than 2 for a wide range ratios of (mean‐free path/probe radius). Detail error estimation is conducted for the orbital motion limited conditions.