Experimental investigation of the electromagnetic effect and improvement of the plasma radial uniformity in a large-area, very-high frequency capacitive argon discharge

Abstract

We performed an experimental investigation on the electromagnetic effect and the plasma radial uniformity in a larger-area, cylindrical capacitively coupled plasma reactor. By utilizing a floating hairpin probe, dependences of the plasma radial density on the driving frequency and the radio-frequency power over a wide pressure range of 5–40 Pa were presented. At a relatively low frequency (LF, e.g. 27 MHz), an evident peak generally appears near the electrode edge for all pressures investigated here due to the edge field effect, while at a very high frequency (VHF, e.g. 60 or 100 MHz), the plasma density shows a sharp peak at the discharge center at lower pressures, indicating a strong standing wave effect. As the RF power increases, the center-peak structure of plasma density becomes more evident. With increasing the pressure, the standing wave effect is gradually overwhelmed by the ‘stop band’ effect, resulting in a transition in the plasma density profile from a central peak to an edge peak. To improve the plasma radial uniformity, a LF source is introduced into the VHF plasma by balancing the standing wave effect with the edge effect. A much better plasma uniformity can be obtained if one chooses appropriate LF powers, pressures and other corresponding discharge parameters.

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

“…Due to continuous growth in both the driving frequency and the wafer size, plasma non-uniformities caused by the standing wave effect have become a major challenge in the material etching and film deposition processes. To optimize the plasma uniformity, several methods have been put forward, such as the use of specially shaped electrodes, [163][164][165][166][167] phase-shift control, [168][169][170] the use of the dual-frequency or multi-frequency source, [133,138,139,171,172] discharge symmetry control, [173,174] etc.…”

“…[168][169][170] This is the so-called "phase-shift control" method. Besides, the dual-frequency [138,139,171,172] or multi-frequency [133] source can be used as an alternative way to optimize the plasma uniformity. By using a two-dimensional plasma model, Bera et al [171] found that the plasma distribution can be effectively controlled by mixing VHF source powers at 60 MHz and 180 MHz.…”

“…24(b)). The method to optimize the plasma uniformity by balancing the SWE with the edge effect was also examined recently by Han et al [172] in a larger CCP reactor with 450 mm diameter electrodes. Using a fast 2D axisymmetric fluid-analytical plasma reactor model, Kawamura et al [133] studied the electromagnetic effects in multi-frequency (2 MHz/60 MHz/162 MHz) CCP in argon.…”

Axial uniformity diagnosis of coaxial surface wave linear plasma by optical emission spectroscopy

“…In figure 13, a short summary of uniformity analysis under four typical experimental conditions is shown as column chart. The uniform coefficient [57] is utilized for evaluating the plasma axial uniformity, which is calculated from the following equation:…”