Essential points for precise etching processes in pulse-time-modulated ultrahigh-frequency plasma

Since ultrahigh-frequency (UHF) plasma has a low electron temperature (less than 2 eV) and uniform density, the effects of electron confinement due to the sheath potential barrier or plasma potential distributions are less prominent than with electron cyclotron resonance plasma or inductive coupled plasma. Consequently, multiple cusp magnetic fields are needed to maintain pulsed UHF plasma even at pulse intervals of a few tens of mu s and they can significantly improve the etching rate and etching selectivity. Moreover, the characteristics of pulse-time-modulated plasma strongly depend on the substrate position from the generation region to the downstream region. Near the plasma generation region, pulsed plasma can be used to produce a higher rate and higher selectivity for polycrystalline silicon etching, compared with a continuous discharge. By transporting the plasma from the generation region to the downstream region, however, improvements in the etching characteristics of the pulsed plasma are gradually reduced. (C) 1997 American Vacuum Society.