Complex transients of input power and electron density in pulsed inductively coupled discharges

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This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency (rf) inductively coupled plasma (ICP) in a mixture of Ar and O2. The densities of the negative ion and the electron, as well as their ratio, i.e., the electronegativity, are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe, under different pressures and O2 contents. Meanwhile, the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a spectrograph. It was found that by increasing the applied power, the electron density and the optical emission intensity show a similar trench, i.e., they increase abruptly at a threshold power, suggesting that the E to H mode transition occurs. With the increase of the pressure, the negative ion density presents opposite trends in the E-mode and the H-mode, which is related to the difference of the electron density and energy for the two modes. The emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O2 content, indicating that the density of high-energy electrons, which can excite atoms, is monotonically decreased. This leads to an increase of the negative ion density in the H-mode with increasing the pressure. Besides, as the applied power is increased, the electronegativity shows an abrupt drop during the E- to H-mode transition.

Section: Resultsmentioning

confidence: 94%

“…More details about the chamber can be found elsewhere. [19][20][21][22][23] A commercial Langmuir probe [24][25][26][27][28][29] (Impedans ALP System TM ) is used to measure the electron density at the axial center and 3 cm below the quartz window. The probe tip is made of tungsten wire with 10 mm in the length and 0.3 mm in the diameter.…”

Section: Methodsmentioning

confidence: 99%

Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O₂ plasma*

Gao

Wang

et al. 2021

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“…[13,87,[101][102][103][104][105] As the pulse ignition is a non-equilibrium process, high-resolution timedependent diagnostics are indispensable for the determination of the dynamic evolution of plasma parameters. [79,106,107] Gao et al [108] measured the temporal evolution of the input power and the electron density in a pulse-modulated ICP in argon, and examined the effects of the RF power and gas pressure. It was found that during the initial stage of the pulse-on period, the input power exhibits two maxima, and meanwhile the electron density was observed to exhibit an overshoot at a high power and a low pressure.…”

Section: -12mentioning

confidence: 99%

Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

Liu¹,

Zhang²,

Zhao³

et al. 2022

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Two classic radio-frequency (RF) plasmas, i.e., the capacitively and the inductively coupled plasma (CCP and ICP), are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures (mTorr ~ Torr), high-frequency electric field (13.56 MHz ~200 MHz), reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas, and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.

“…This density peak may be caused by the release of charge by capacitance and inductance in RF power resource. [20] Figure 2(c) displays the temporal evolutions of effective electron temperature at different axial positions. It can be seen from the diagram that the effective electron temperature is high when the power is turned on, and then decreases gradually.…”

Section: Axial Distribution In Ar Dischargementioning

confidence: 99%

“…The study of overshoot phenomenon is beneficial to understand it and improve the uniformity of plasma. The temporal evolutions of input power and electron density in Ar and Ar/CF 4 pulsed ICP were investigated by Gao et al [20] They found that the input power appears two peaks and the electron density presents an overshoot during the initial pulse-on stage, and the overshoot decays at lower powers and higher pressures. The work in this paper goes into the previous work by focus more on the dependence of overshoot phenomenon on spatial positions.…”

Section: Introductionmentioning

confidence: 99%

Spatio-temporal measurements of overshoot phenomenon in pulsed inductively coupled discharge*

Lv¹,

Gao²,

Zhang³

et al. 2021

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Pulse inductively coupled plasma has been widely used in the microelectronics industry, but the existence of overshoot phenomenon may affect the uniformity of plasma and generate high-energy ions, which could damage the chip. The overshoot phenomenon at various spatial locations in pulsed inductively coupled Ar and Ar/CF4 discharges is studied in this work. The electron density, effective electron temperature, relative light intensity, and electron energy probability function (EEPF) are measured by using a time-resolved Langmuir probe and an optical probe, as a function of axial and radial locations. At the initial stage of pulse, both electron density and relative light intensity exhibit overshoot phenomenon, i.e., they first increase to a peak value and then decrease to a convergent value. The overshoot phenomenon gradually decays, when the probe moves away from the coils. Meanwhile, a delay appears in the variation of the electron densities, and the effective electron temperature decreases, which may be related to the reduced strength of electric field at a distance, and the consequent fewer high-energy electrons, inducing limited ionization and excitation rate. The overshoot phenomenon gradually disappears and the electron density decreases, when the probe moves away from reactor centre. In Ar/CF4 discharge, the overshoot phenomenon of electron density is weaker than that in the Ar discharge, and the plasma reaches a steady density within a much shorter time, which is probably due to the more ionization channels and lower ionization thresholds in the Ar/CF4 plasma.