High-density flat plasma production based on surface waves

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 (omega(p) much greater than omega)-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.