Degree of Cl₂ dissociation and etching characteristics in high-density plasmas

At the same input power (1000 W), inductive coupled plasma (ICP) and ultrahigh-frequency (UHF) plasma sources produced electron densities of 1 X 10¹¹ cm^-3 at 3.5 mTorr, yet the UHF plasma was much less dissociated (30%) than the ICP (70%). This can be attributed to differences in the electron energy distribution functions between the ICP and the UHF plasma, especially at low pressure. Under these conditions, Al etching profiles and doped poly-Si-etching rates were investigated to determine how the degree of dissociation influences etching reactions. UHF plasmas produced completely anisotropic Al and poly-Si etching independent of the dopant used when Cl₂ was feed gas, whereas under the same conditions, the ICP produced isotropic Al etching profiles and the poly-Si-etching rate was strongly dependent on the dopant used under the same conditions. This implies that the degree of dissociation strongly influences the surface reaction in a high-density Cl₂ plasma.