Operating high-density plasma sources in a low-density range: Applicationsto metal etch processes

A new way of operating high-density plasma sources is presented which allow s the resist/metal selectivity to be significantly increased during a metal etching process while maintaining the anisotropy of the etching profile. T he principle of the technique is to operate a high-density plasma source in a low-density range in which the radio-frequency (rf) source power is lowe r than the chuck power. When the source is operated under these conditions, the ion density is strongly decreased while the source is still operated a t low pressures. Optical emission spectroscopy has been used to compare the dissociation efficiency of the source operated in the low- and high-densit y modes. The photoresist etch rate was measured using light reflectometry. In some cases, after etching, the resist sample was transferred in vacuo in to an x-ray photoelectron spectrometer analysis chamber to measure the chlo rine coverage on the resist surface. The ion current density (J(i)) was det ermined using a new type of electrostatic probe. The ion flux was determine d from the discharging of a RF-biased capacitance in series with the probe. Finally, a simple model is suggested to explain the impact of the plasma o perating conditions (source power and chuck power) on the resist etch rate. (C) 1999 American Vacuum Society. [S0734-2101(99)03305-9].