Plasma properties determined with induction loop probes in a planar inductively coupled plasma source

Abstract

Electromagnetic fields in a planar rf inductively coupled plasma source, of interest for materials processing, were measured using a two-loop inductive ͑B-dot͒ probe. The two loops were oriented to measure the time derivative of the axial and radial components of the magnetic field Ḃ z and Ḃ r , respectively, at various positions in the r -z plane of the cylindrically symmetric argon discharge. Maxwell's equations were used with this data to calculate amplitudes of the rf azimuthal electric field E and current density J , as well as the complex permittivity ⑀ of the plasma, from which the electron density n e was calculated. The electron densities calculated using this technique were found to compare favorably to the results of measurements made with Langmuir probes. Electron drift velocities calculated from J and n e were found to be comparable to electron thermal velocities in the region of highest E and thus may contribute to local enhancement of electron impact reactions, thereby affecting process chemistry and uniformity. The peak in the drift velocity moved radially outward as the pressure increased due changes in the radial plasma density profile. This technique is applicable to chemistries where Langmuir probes are not practical.

A reply to a comment on: `On the plasma parameters of a planar inductive oxygen discharge

“…The electron density shown in figure 5(a) increases from the centre plane of the discharge and peaks at roughly r/R = 0.5. As discussed by Hopwood et al [22], Meyer and Wendt [23] and Meyer et al [24] the inductive electric field and thus the absorbed power peak at approximately one-half the radius of the coil and go to zero in the centre of the discharge. The effective electron temperature, shown in figure 5(b), increases slightly towards the chamber wall.…”

Angular anisotropy of electron energy distributions in inductively coupled plasmas

“…For example, measurements of electron drift velocities in the skin layer of an ICP reactor at 10 and 50 mTorr by Meyer et al were found to be comparable to the local electron thermal velocities, which suggests that the AEEDs were considerably anisotropic. 16 Kolobov et al computationally investigated the angular distribution of electrons in an ICP having a coaxial solenoidal coil. 17 They found that the angular distribution of electrons with energies above the plasma potential was anisotropic in the radialaxial (rz) plane and that this anisotropy depends on the radial position ͑distance from the coil͒.…”

Magnetic induction and plasma impedance in a planar inductive discharge

“…Electromagnetic field measurements have been reported for planar inductively coupled discharges [5][6][7]. Hopwood et al [5] measured the magnitude of the magnetic induction to be in the range of 0.2-0.7 mT at the window and to decay exponentially as a function of distance from the window.…”