New ultrahigh-frequency plasma discharge for overcoming the limitations of etching processes

Electron, ion, and neutral temperatures are measured in an ultrahigh-frequency (UHF) plasma by Langmuir probe and Doppler-shifted laser-induced fluorescence. The electron, ion, and neutral temperatures are found to be 1.5-2.0 eV (Ar plasma), 0.066 eV for Ar+, and 0.036 eV for Ne, respectively, and are lower than those reported for electron cyclotron resonance and helicon wave plasmas. The low temperatures cause lower dissociations of CHF3 gas even in the plasma production region of the UHF plasma source. The plasma is expected to dramatically improve the selectivity of SiO2 to the underlying Si. Additionally, the plasma can be used to accomplish a notch-free poly-Si etching profile and microloading-free Si trench etching with a high etching rate and high anisotropy with a narrow space pattern of less than 0.3 mu m. It is suggested that the charge accumulation with the narrow space pattern is eliminated because of the low electron temperature in the UHF plasma. (C) 1996 American Vacuum Society.