Spatial and frequency dependence of plasma currents in a 300 mm capacitively coupled plasma reactor

Abstract

There is much interest in scaling rf-excited capacitively coupled plasma reactors to larger sizes and to higher frequencies. As the size approaches operating wavelength, concerns arise about non-uniformity across the work piece, particularly in light of the well-documented slow-surface-wave phenomenon. We present measurements and calculations of spatial and frequency dependence of rf magnetic fields inside argon plasma in an industrially relevant, 300 mm plasma-processing chamber. The results show distinct differences in the spatial distributions and harmonic content of rf fields in the plasma at the three frequencies studied (13.56, 60 and 176 MHz). Evidence of a slow-wave structure was not apparent. The results suggest that interaction between the plasma and the rf excitation circuit may strongly influence the structures of these magnetic fields and that this interaction is frequency dependent. At the higher frequencies, wave propagation becomes extremely complex; it is controlled by the strong electrical nonlinearity of the sheath and is not explained simply by previous models.

Electric field filamentation and higher harmonic generation in very high frequency capacitive discharges

“…Another interesting feature of VHF CCP devices is the presence of higher harmonics of the applied frequency in the current and voltage characteristics of the discharges. Using a B-dot probe, Miller et al [22] detected the presence of higher harmonics in the electric field of the bulk plasma at a driving frequency of 60 and 176 MHz. Upadhyay et al [23] performed numerical simulations of electromagnetic wave phenomena in an asymmetric CCP excited at 60 MHz and showed the presence of higher harmonic content in the electric field up to the 20th harmonic of the excitation frequency.…”

Simulations of electromagnetic effects in high-frequency capacitively coupled discharges using the Darwin approximation

“…The fields are calculated self-consistently with evolution of the electron plasma component using (13) to (15)). One can distinguish two different sets of boundary conditions depending on the way the discharge is driven, either with a voltage source or a current source.…”

“…One can distinguish two different sets of boundary conditions depending on the way the discharge is driven, either with a voltage source or a current source. Whereas boundary conditions for (15) are same for both cases (see the discussion at the end of section III), the boundary conditions for (13) and (14) are different for each case.…”

Comparison of electrostatic and electromagnetic simulations for very high frequency plasmas

“…In recent years, several theoretical studies [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and experimental research [22][23][24][25][26][27][28][29][30] have been published on the plasma characteristics in a CCP sustained by VHF sources. Lieberman et al 6 first employed a uniform slab model to investigate the standing-wave and skin effects in VHF discharges.…”

“…Subsequently they performed measurements in large area rectangular reactors, showing that a thin conducting layer present on the dielectric plate was sufficient to screen the electrode shape effect. 24 Miller et al 25,26 reported the magnetic field and other plasma parameters, for instance, line-integrated electron density and ion saturation current, as a function of frequency. Recently, Ahn and Chang 27 revealed, by means of a Langmuir probe and a B-dot probe, that the strong plasma inhomogeneity, detected in a cylindrical high frequency capacitive discharge at high pressures, was created by the significant inductive electric field near the radial edge.…”