Electrostatic ion cyclotron wave fields are determined in a magnetized and weakly collisional plasma. A phased-locked Laser Induced Fluorescence (LIF) diagnostic is used to directly measure the wave perturbed ion velocity distribution. Comparing these local LIF measurements with a theoretical model uniquely determines the wave parameters, such as the wave potential, the three-dimensional wave vector, and the effective wave damping. The self-consistent wave–particle interaction is modeled by Boltzmann–Poisson equations in the limit of weak collisions. The wave parameters determined from local measurements agree with those determined from spatial scans.

Articles you may be interested inDetection of electron energy distribution function anisotropy in a magnetized electron cyclotron resonance plasma by using a directional Langmuir probe Phys. Plasmas 21, 073510 (2014); 10.1063/1.4890350Optical emission spectroscopy and Langmuir probe diagnostics of CH3F/O2 inductively coupled plasmasThe Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes Rev.Diagnostics of inductively amplified magnetron discharges by optical emission, absorption spectroscopy, and Langmuir probe measurements Langmuir probe theory, adapted to magnetized, partially ionized, low temperature processing plasmas with radial diffusion dominated by electron-neutral collisions, was verified in electron cyclotron resonance ͑ECR͒ plasmas. Plasma parameters such as plasma potential, electron temperature, plasma density, and the ratio of electron saturation current to ion saturation current (I e */I i *) were measured by single-sided planar probe in various ECR plasmas ͑H 2 , He, N 2 , O 2 , Ar, and CF 4 ͒. The neutral pressure was varied between 0.5 and 8.5 mTorr and the microwave power between 170 and 1250 W with good matching conditions; the reflected power was kept at less than 3% of the input power. The measured ratios of I e */I i * , and other plasma parameters were consistent with the probe theory for pressures greater than 2.0 mTorr for various plasmas of Ar, He, H 2 , and N 2 . These results indicate that the electron-neutral collisional probe theory works well for magnetized ECR plasmas ͑magnetic flux densities of 0.8-1.0 kG͒.

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The electron density, the electron kinetic energy, the particle motion, and electric fields in a coaxial positive-polarity plasma opening switch (POS) were studied using spectroscopic diagnostics. A gaseous source that injects the plasma radially outward from inside the inner POS electrode was developed. The plasma was locally seeded with various species, desired for the various measurements allowing for axial, radial, and azimuthal resolutions both prior to and during the 180 ns long current pulse. The electron density was determined from particle ionization times and the electron energy from line intensities and time dependent collisional-radiative calculations. Fluctuating electric fields were studied from Stark broadening. The ion velocity distributions were obtained from emission-line Doppler broadenings and shifts. The early ion motion, the relatively low ion velocities and the nearly linear velocity dependence on the ion charge-to-mass ratio, leads to the conclusion that the magnetic field penetrates the plasma early in the pulse. The ion velocity dependence on the axial location were thus used to infer the time dependent axial distribution of the magnetic field, indicating the formation of a relatively high current density at the load-side edge of the plasma. This is expected to cause plasma acceleration towards the load, found to be supported by charge-collector measurements. The fast magnetic field penetration could be explained by mechanisms based on the Hall effect.

Real-time etch rate of thin transparent films is determined within seconds by an in-situ two-color laser interferometer. The use of two colors improves the accuracy of the calculated rates, provides an absolute measure of film thickness for endpoint prediction, and differentiates between etching and deposition. The tool state parameters, rf power to the antenna and the wafer stage, gas pressure and flow rates, are computer controlled and monitored. Real-time etch rate characterization is obtained by monitoring the etch dependence on varying tool state parameters. The density of the etch radicals, chlorine and fluorine, is obtained with xenon and argon actinometry using optical emission and mass spectra. An etch rate model, based on the input power to the wafer stage and the relative density of the etch radicals, is used to develop a model-based real-time control algorithm. This algorithm has been used to control the etch rate of unpatterned polysilicon and SiO2.

The chlorine contents of 40 kHz and 13.56 MHz RF silicontetrachloride and dichlorosilane plasmas were investigated using actinometric evaluation in a parallel-plate (stainless-steel disk electrodes, stainless-steel reactor) electrode and in an electrodeless (external electrodes and glass reactor) discharges, in the 50-500 W RF power and 100-500 mTorr pressure ranges. It was found that the frequency has a significant effect on the molecular fragmentation of dichlorosilane and a less important effect on the fragmentation of silicontetrachloride. This behaviour was related to the molecular structures of the two starting components. The plasma-induced surface chemistries and morphology changes were also investigated and related to the different chemistries driven under 40 kHz and 13.56 MHz frequency environments. Plasma-induced and frequency-controlled molecular fragmentation reactions can be envisaged based on these findings.

Nonthermal turbulent electric fields due to plasma instabilities were studied in a 100-ns duration plasma opening switch using observations of hydrogen line spectral profiles. The H ␣ and H ␤ widths were seen to rise by 2-3 times during the current pulse, shown to result from the presence of nonthermal electric fields in the plasma. The spectral profiles are analyzed using two recently developed methods based on short and intermediate time behaviors of the line profile Fourier transforms. One method gives the mean amplitude of the nonthermal fields with no dependence on their frequencies. The second method uses calculations of the autocorrelation functions for various field amplitudes and frequencies to yield bounds on these two parameters. The field amplitude is determined to be 14.5Ϯ2.5 kV/cm, and the fluctuation frequency is found to be of the order of the electron plasma frequency. Based on their high frequency, the oscillations probably result from Langmuir waves, driven by the voltage drop on the plasma opening switch ͑POS͒. The waves have no significant effect on the POS operation, since they do not give rise to anomalous resistivity, and therefore have no effect on the magnetic-field evolution. We obtain an upper limit for the amplitude of possible low-frequency fields ͑ion-acoustic waves͒, that may give rise to anomalous resistivity, and estimate the resulting diffusion velocity and current channel width. Both quantities are found to be much lower than the values observed in the experiment, and the low-frequency field amplitude is much lower than the saturation limit predicted by previous theoretical treatments. This implies that in our experiment possible low-frequency waves have little influence on the magnetic-field distribution.

A novel electro-optical probe ͑EOP͒ has been developed to characterize the spatial uniformity of various plasma parameters. Spatially resolved electron density and energy distribution function, neutral and charged particle densities, as well as ion flow velocity are determined by the EOP. The design of the EOP combines a Mach probe, back-to-back charge collectors, and a collimated optical fiber. The light collection angle of the optical fiber is limited by recessing the fiber in a ceramic tube. The line-of-sight integration length of the plasma emission is bounded by the charge collector disk. A spatial resolution of 2.4 cm is obtained by the present design of the EOP. The ion flow velocity perpendicular to the charge collector surface is determined by the ratio of the ion saturation currents of the two counter facing charge collectors. Localized actinometry, that combines spatially resolved optical emission spectra and electron energy distribution functions, is used to determine the density of atomic chlorine and fluorine radicals. The spatial distribution is obtained by scanning the EOP across the plasma volume.