Development of Simple Designs of Multitip Probe Diagnostic Systems for RF Plasma Characterization (original) (raw)
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Multi-tip Probe Diagnostics for Plasmas: Designs and Applications
2014
Electrostatic probes are considered to be the most powerful and experimentally simplest tools for characterization of low temperature plasmas. Up until now, different pure metals have been tested as a probe tip material; however, it would be hard to find any literature on the use of nickel-chrome alloy as a probe tip material. The objective of the work was to develop nickel-chrome multi-tip Langmuir probes for characterization of inductively coupled nitrogen plasmas. In order to meet the research objectives, symmetric and asymmetric double probes and symmetric triple probe diagnostic systems with their necessary driving circuits were developed and used to characterize the inductively coupled nitrogen plasma generated with a 13.56 MHz RF source and an impedance matching network. Using the DC properties of these laboratory manufactured multi-tip probes, the plasma parameters like ion saturation current, electron temperature, electron number density, individual probe currents and electron energy probability function were measured as a function filling pressure, RF power and radial distance of the probe from chamber wall. The nitrogen flow rate was kept constant at 50 sccm and reflected power less than 2% throughout the conduced experiments. The results from the all three probes were compared to check their workability in low temperature RF plasmas. From the obtained data, it was noticed that the electron temperature and number density increase with an increase in RF power. However, a decreasing trend in these parameters was evident for any increase in filling gas pressure or the probe distance from the chamber wall. The highest electron temperatures and densities were found near the chamber centerline (14 cm). The overall results were confirming the highest electron temperatures measured with asymmetric double probe followed by a symmetric double and triple probe. Nevertheless, the electron number density measured with asymmetric double probe was somewhat lower than that measured with symmetric triple probe. In addition, Electron Energy Probability Function (EEPF) was also measured by using an asymmetric double probe as a function of filling gas pressure and input power. It was noticed that EEPF evidently deviates from the Maxwellian behavior particularly at low filling pressures.
A Comparative Study of Single and Double Langmuir Probe Techniques for RF Plasma Characterization
Contributions to Plasma Physics, 1999
In this study, the plasma density and electron temperature of Radio Frequency (RF) plasmas were determined by three types of Langrnuir probes, namely a conventional double probe, a single probe with RF, choke and a single probe with RF choke and compensating electrode. The same plasmas were characterized by the three probes, each performing three measurements per plasma condition, in order to determine the precision of the measurement results. After performing a comparative analysis, which looked at the precision and the accuracy of these results, .the conclusion is that the double probe, which has already the advantage of the simplest construction, yields the most reliable results for both capacitively and inductively coupled RF plasmas. The single probe with RF choke and compensating electrode has a similar precision as the single probe without compensating electrode, but its accuracy is better.
International Journal of Applied Physics and Mathematics
Low temperature radio frequency plasma is widely used in low temperature plasma processing medium for material processing in many fields including microelectronics, aerospace, and the biology. For proper utilization of the process, it is very much important to know the plasma parameters. In this paper a technique is reported to determine the plasma parameters from the electrical discharge characteristic of a capacitivly couple radio frequency argon plasma. The homogeneous discharge model is modified to make it applicable in low pressure by incorporating the plasma series resonance effect. The effect on the plasma resistance by the change in drift velocity of the electron with rf electric filed is also considered. The electron density and temperature is found to be well agreed with the Langmuir probe diagnostic result, which is in the range of 0.5x10 10 to 4.5x10 10 cm-3 and 1.4 to 1.6 ev for wide range of rf power. Index Terms-Capacitive couple radio frequency plasma, discharge characteristic, homogeneous discharge model, plasma parameters, power balance.
Diagnostics and Simulation of Low-Frequency Inductively Coupled Plasmas
AIP Conference Proceedings, 2003
The results on the diagnostics and numerical modeling of low-frequency (~460 KHz) inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil are presented. Experimental data on the electron number densities and temperatures, and optical emission intensities of the abundant plasma species in low/intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different RF powers and working gas pressures, using the 2D fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating at higher (> 1 kW ) RF powers is among the key factors that control the electron number density and temperature. The dependence of the average RF power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
A new double probe system for studies of non-uniform plasmas
Brazilian Journal of Physics, 2003
A theoretical and experimental study was developed about the applicability of a double probe system consisting of two directional Langmuir probes, both probes being located separately in a plasma column. The current-voltage characteristic of the double probe was obtained considering a plasma with a drifting maxwellian electron velocity distribution function and stationary ion background. In deriving the characteristic of the double probe, the plasma parameters, namely, electron temperature (T e), electron density (N e), electron drift velocity (V de) and plasma potential (Vp) are assumed to be non-uniform. The double probe characteristic is also dependent on the angle between the axial direction of the electron drift and the normal to the collecting area of the probe. Each probe can be rotated such that this angle can be varied between zero and 180 degrees. Various probe characteristics were simulated using plasma parameters obtained by independent single probe measurements in the positive column of a low-pressure arc discharge in mercury vapor. Typical parameters of the positive column, used in the simulation, are: Te = 5 eV, Ne = 10 17 m −3 , v de = 8x10 5 ms −1. Experimental characteristics of the double probe were obtained and compared with the simulated results, showing good agreement. It is concluded that this directional probe system can be a reliable diagnostic tool especially for studies of non-uniform plasmas. 2.1 Derivation of the double probe characteristic equation In this analysis, we consider the electron and ion current collected by a double planar probe in non-uniform plasma with
Journal of Physics: Conference Series, 2012
We present the design of a system for probe diagnostics and the results obtained for the plasma parameters in a small portable microwave plasma source operating at atmospheric pressure. The average electron temperature and the argon plasma density in the discharge are estimated from the current-voltage (I-V) characteristics of an asymmetric double probe. The calculated value of the electron temperature is T e ~1.7±0.3 eV. Three models for the probe ion saturation current in a flowing plasma at atmospheric pressure are applied to calculating the plasma density. The calculated value of the plasma density varies with the input power P = 15-25 W and gas flow rate 250-350 sccm. The plasma density estimations obtained by the models lie within a wide range and are compared with results from optical diagnostics.
Comparative analyses of plasma probe diagnostics techniques
Journal of Applied Physics, 2015
The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to ine...
Electrostatic probe diagnostics of a planar-type radio-frequency inductively coupled oxygen plasma
Journal of Applied Physics, 2001
An inductively coupled oxygen radio-frequency ͑13.56 MHz͒ discharge is investigated based on modeling and experiment. Experimental measurement is done at a range of gas pressure of 1-30 mTorr, and rf power of 100-1000 W. We measure most of the important plasma parameters such as the densities of charged species, electron temperature, plasma potential, and electron energy distribution function. The measured values are compared with the results of the spatially averaged global model. We observe a generally good agreement between the modeling and the experiment. The scaling features, the transition of the operating region, and the radial distributions of charged species are also discussed.
Rf probe technology for the next generation of technological plasmas
Journal of Physics D: Applied Physics, 2001
We describe radio frequency (rf) analysis of technological plasmas at the 13.56 MHz fundamental drive frequency and integer narrow-band harmonics up to n = 9. In particular, we demonstrate the use of harmonic amplitude information as a process end-point diagnostic. Using very high frequency (vhf) techniques, we construct non-invasive ex situ remote-coupled probes: a diplexer, an equal-ratio-arm bridge, and a dual directional coupler used as a single directional device. These probes bolt into the plasma-tool 50 transmission-line between the rf generator and matching network, and hence do not require modification of the plasma tool. The 50 probe environment produces repeatable measurements of the chamber capacitance and narrow-band harmonic amplitude with an end-point detection sensitivity corresponding to a 2 dB change in the harmonic amplitude with the removal of 1 cm 2 of photoresist. The methodology and design of an instrument for the measurement of the plasma-tool frequency response, and the plasma harmonic amplitude and phase response are examined. The instrument allows the monitoring of the plasma phase delay, plasma-tool short-and long-term ageing, and process end-point prediction.
Electron energy distribution functions (EEDFs) have been measured in a cylindrical inductively coupled plasma (ICP) with a planar coil over a wide range of external parameters (argon pressure, discharge power and driving frequency). The measurements were performed under well-defined discharge conditions (discharge geometry, rf power absorbed by plasma, external electrical characteristics and electromagnetic field and rf current density profiles). Problems found in many probe measurements in ICPs were analysed and a rationale for designing probe diagnostics that addresses these problems is presented in this paper. A variety of plasma parameters, such as, plasma density, effective and screen electron temperatures, electron-atom transport collision frequency, effective rf frequency and rates of inelastic processes, have been found as appropriate integrals of the measured EEDFs. The dependence of these ICP parameters over a wide range of argon pressure, rf power and frequency results in experimental scaling laws that are suitable for comparison with ICP models and helpful in ICP design for many applications.