Electron and ion kinetics in magnetized capacitively coupled plasma source

Abstract

One-dimensional particle-in-cell Monte Carlo collision simulations of magnetized argon plasmas in an asymmetric capacitively coupled plasma reactor are presented. At low pressure (10mTorr), electron kinetics are strongly affected by the magnetic field and transitions from nonlocal to local kinetic property occur with increasing magnetic field which are reflected in spatially resolved calculations of the electron-energy probability function. For high-energy electrons, the transition takes place when the energy-relaxation length is smaller than the system length. For low-energy electrons, however, the transition occurs when the electron-diffusion time scale in the energy space is shorter than the spatial-diffusion time scale in coordinate space. These observations are in agreement with experimental data and theoretical calculations deduced from the Boltzmann equation. The ion energy distribution function (IEDF) on the driven electrode changes from the ion-neutral collisional type to the ion-neutral collisionless type with increasing magnetic field strength. The maximum ion energy in the IEDF decreases and the angular spread in the ion angle distribution function slightly increases with increasing magnetic field strength. These changes are explained in terms of the ratio of the ion-transit time to rf frequency, the sheath length, and the mean potential difference between the driven electrode and the plasma. At high pressure (218mTorr), electron-neutral collisions disrupt electron gyromotion so that the effects of the magnetic field on electron and ion kinetics are greatly reduced.

Influence of metastable atoms in low pressure magnetized radio-frequency argon discharges

“…From figure 2(b), the electron temperature T e at the center of the discharge rises with increasing the magnetic field and peaks at about 2.5 eV. The increase of T e in the magnetic field range from 0 G to 20 G is consistent with the previous measurement [4,36] and simulation [37] results. The increase of T e in the bulk plasma can be attributed to the enhanced heating of low-energy electrons at low pressures, as will be shown in figure 4.…”

Electron power absorption dynamics in magnetized capacitively coupled radio frequency oxygen discharges

“…Magnetized CCPs are frequently used for such applications and have shown good performance in improving distinct plasma properties, especially the plasma density [8][9][10]. Typically the magnetic field is oriented parallel to the electrodes to limit the cross-field transport of electrons to the walls.…”

Evolution of electron temperature in low pressure magnetized capacitive plasma

“…[5][6][7][8] This nonmonotonic change of electron temperature with the magnetic field was shown to be a combined effect from suppressing electron bounce resonance heating and enhancing collisional heating while increasing the magnetic field. The result shows that the electron temperature of low pressure capacitive discharge evolved nonmonotonically with increasing magnetic field, which is a noticeable result because according to the previous studies, the electron temperature increased with the magnetic field.…”

“…[1][2][3] However, in the nonmaxwellian electron plasma which is conventional one in partially ionized plasma, the electron temperature which is represented by an inverse slope of the electron energy distribution in specific energy range ͓T e ϰ ͑‫ץ‬f / ‫͒⑀ץ‬ −1 , f is electron energy distribution functions ͑EEDFs͔͒ or by an effective electron energy ͑T e = T eff =2/ 3͗⑀͘ =2/ 3͐⑀fd⑀ / ͐fd⑀, where ⑀ is electron kinetic en-ergy͒ is influenced and determined by specific electron heating/loss mechanisms sustaining the discharge source, which changes depending on the plasma density, discharge power, and pressure. [5][6][7][8] However, the application and validation of the results form previous studies that the electron temperature increases with the magnetic field still seems questionable, which will be shown later in Fig. Among these external parameters, the magnetic field is known to affect the electron heating and loss processes greatly by changing the electrodynamics in the plasma, 2 thus the magnetic field has been used recently as an additional knob in the plasma processing to control the electron temperature in order to enhance some desirable features of specific plasma sources and processing results.…”

“…17 The reasons why the previous studies 5,7,8 have not measure this abnormal behavior of electron temperature is that the experimental/simulation condition is not suitable to make at least one collisionless electron bounce motion in the ambipolar potential 11 too high pressure ͑50 mTorr͒ and big gap length ͑Ͼ10 cm͒ for Ref. 17 The reasons why the previous studies 5,7,8 have not measure this abnormal behavior of electron temperature is that the experimental/simulation condition is not suitable to make at least one collisionless electron bounce motion in the ambipolar potential 11 too high pressure ͑50 mTorr͒ and big gap length ͑Ͼ10 cm͒ for Ref.…”