Probe diagnostics of non-Maxwellian plasmas

Godyak, Valery; Piejak, R. B.; Alexandrovich, B. M.

doi:10.1063/1.352924

Cited by 292 publications

(207 citation statements)

References 8 publications

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“…Sheridan et al 51 reported them for dc discharges in helium and Godyak et al 52 analyzed different non-Maxwellian plasmas with probe diagnostics. In the field of pulsed plasmas, Bäcker and Bradley 37 thoroughly investigated the effects of incorporating magnetrons into the plasma parameters, such as, for instance, the generation of bi-Maxwellian discharges induced by the presence of a magnetic field.…”

Section: ͑7͒mentioning

confidence: 99%

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

Corbella

Rubio‐Roy

Bertrán

et al. 2009

Journal of Applied Physics

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Here we approximate the plasma kinetics responsible for diamondlike carbon ͑DLC͒ depositions that result from pulsed-dc discharges. The DLC films were deposited at room temperature by plasma-enhanced chemical vapor deposition ͑PECVD͒ in a methane ͑CH 4 ͒ atmosphere at 10 Pa. We compared the plasma characteristics of asymmetric bipolar pulsed-dc discharges at 100 kHz to those produced by a radio frequency ͑rf͒ source. The electrical discharges were monitored by a computer-controlled Langmuir probe operating in time-resolved mode. The acquisition system provided the intensity-voltage ͑I-V͒ characteristics with a time resolution of 1 s. This facilitated the discussion of the variation in plasma parameters within a pulse cycle as a function of the pulse waveform and the peak voltage. The electron distribution was clearly divided into high-and low-energy Maxwellian populations of electrons ͑a bi-Maxwellian population͒ at the beginning of the negative voltage region of the pulse. We ascribe this to intense stochastic heating due to the rapid advancing of the sheath edge. The hot population had an electron temperature T e hot of over 10 eV and an initial low density n e hot which decreased to zero. Cold electrons of temperature T e cold ϳ 1 eV represented the majority of each discharge. The density of cold electrons n e cold showed a monotonic increase over time within the negative pulse, peaking at almost 7 ϫ 10 10 cm −3 , corresponding to the cooling of the hot electrons. The plasma potential V p of ϳ30 V underwent a smooth increase during the pulse and fell at the end of the negative region. Different rates of CH 4 conversion were calculated from the DLC deposition rate. These were explained in terms of the specific activation energy E a and the conversion factor x dep associated with the plasma processes. The work deepens our understanding of the advantages of using pulsed power supplies for the PECVD of hard metallic and protective coatings for industrial applications ͑optics, biomedicine, and electronics͒.

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Section: ͑7͒mentioning

confidence: 99%

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

Corbella

Rubio‐Roy

Bertrán

et al. 2009

Journal of Applied Physics

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“…As it has been described in §IV about the ionic part of the I-V characteristic, we fit the data to equation (16) determining the values for the constants γ, β and C 0 . These values are summarized in Table 1.…”

Section: Least-squares Fittingmentioning

confidence: 99%

“…Considering this value for the temperature T e , we find by equation (21) the density n e = 1.62 × 10 16 m −3 . For the values computed after fitting, it is possible to accomplish the integration of the adjusted characteristic, to obtain [15,16] …”

Section: Least-squares Fittingmentioning

confidence: 99%

A comparative analysis of the electron energy distribution function obtained by regularization methods and by a least-squares fitting

Gutiérrez-Tapia

Llamas

2004

Physics of Plasmas

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Abstract. To establish the electron energy distribution function (EEDF), the second derivative of a Langmuir probe current-voltage (I-V) characteristic is numerically integrated using the Tikhonov singular value decomposition regularized method. A comparison of the numerically intagrated EDDF and by a least-squares fitting is discussed. The used I-V characteristic is measured in an ECR plasma source using a cylindrical probe and the plasma parameters are determined by the Laframboise theory. This technique allows a rapid analysis of plasma parameters at any gas pressure. The obtained EEDF, for the case of the ECR plasma source, shows the existence of two groups of electrons with different temperatures. This result is associated with the collisional mechanism heating taking place in ECR plasma sources, where low pressure plasma is sustained by electron impact ionization of the ground state molecules or atoms by energetic electrons arising in the resonance zone.

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“…This analysis will provide accurate determination of the lower temperature distributions but for the highest energy distribution the measured temperature can be, and often is, inaccurate. 4 This inaccuracy arises since the electron current becomes increasingly sensitive to the removal of the ion saturation current as the high energy tail of the distribution function becomes more depleted. That is, the determination of the electron temperature becomes increasing inaccurate as the electron energy distribution function moves from a Maxwellian type distribution towards a mono-energetic distribution.…”

Section: Introductionmentioning

confidence: 99%

A computerized Langmuir probe system

Pilling¹,

Bydder²,

Carnegie³

2003

Review of Scientific Instruments

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For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of Ϯ70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA-100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier.

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Probe diagnostics of non-Maxwellian plasmas

Cited by 292 publications

References 8 publications

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

A comparative analysis of the electron energy distribution function obtained by regularization methods and by a least-squares fitting

A computerized Langmuir probe system

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