SELF-BIAS REDUCTION IN PLASMA-ETCHING BY A DOUBLE-RING CATHODE

Experimental results are presented which show that the self-bias voltage generated on the cathode of an asymmetric 13.56 MHz etching system system can be significantly reduced by electrically connecting a spatially separated annular ring to the cathode. At low pressures (<10 mu bar) the self-bias voltage of the double (hollow) cathode configuration can be a factor of 10 lower than that of conventional cathodes. Since the energy of ions arriving at the cathode depends on the self bias, this reduction would be reflected in the ion energy distribution. Etch rates of around 1.5 mu m min-1at 10 mu bar and 800 W have been measured with SF6plasmas and polycrystalline silicon. Etch uniformity of +or-5% edge to edge has been measured on a 4 inch wafer. © 1990 IOP Publication Ltd.