High-density flat plasma production based on surface waves

Abstract

Recent development of large-diameter (>30 cm) high-density (>10 11 cm −3 ) microwave plasma production at low pressures (<20 mTorr) without an external DC magnetic field is reviewed in view of application to the next generation ULSI devices and flat panel displays. Understanding the discharge physics-excitation, propagation and absorption of the surface wave in a flat plasma geometry under overdense conditions (ω p ω)-is indispensable for controlling the plasma. Experimental evidence of discrete surface-wave modes is clearly found in optical emission and microwave field measurements. The analysis of the full-wave electromagnetic dispersion successfully identified the observed eigenmodes. Stability analysis of the wave-plasma interaction resulted in a stability criterion predicting hysteresis loops in the power-density dependence, which were found in the experiment. A possibility of collisionless absorption of surface waves, i.e. mode conversion to electron plasma waves at the resonant layer, is discussed with the recent experimental results taken into account. From the plasma technology point of view, examples of surface-wave plasma tools (some of them commercially available) are introduced and the significance of the antenna structure is emphasized. Finally, the advantages of the surface-wave plasma source in comparison with other high-density sources are summarized.

Power transfer and mode transitions in low-frequency inductively coupled plasmas

“…A similar tendency has been reported for microwave slot-excited plasmas, where n e turns out to be stable and is not strongly affected by the inevitable power and pressure fluctuations. 11,16 Furthermore, mode transitions in microwave slot-excited plasmas are also accompanied by minima in the power reflection coefficient, although they appear to be sharper than that reported here for the lowfrequency inductively coupled plasmas. This difference can best be understood by noting that the MSE discharges are sustained by the plasma surface waves.…”

“…1 and 2 one can estimate that the value of P tot required to initiate the transition is approximately 970 W just before the transition, and 1100 W after that. In analogy with the microwave-excited plasma experiments, 11,13 we introduce the rf power reflection coefficient…”

Plasmas meet plasmonics

“…As noted in the introduction, surface wave plasma (SWP) resonance sustained discharges [49] have been investigated for a number of decades, first as a promising diagnostic tool (e.g., elemental and spectral analysis [49]) and more recently as high-density, large-area plasma sources [46]. The use of surface waves in large-area processing has seen them move from an object of purely academic research to a viable fabrication route.…”

“…A typical set-up is shown in Figure 4b [45,46]. Figure 4b shows a standard linear/column set up, with a SW launcher (i.e., surfatron/surfaguide) and a dielectric tube which the plasma is contained in.…”

“…Essentially these TM mns (via a large dielectric plate) are big microwave analogues of localised surface plasmons from the optical range. Examples of discrete, pure surface modes [46] in the microwave frequency range of our interest are: TM 53 , TM 62 , and TM 33 .…”