SiO_2 etching in inductively coupled plasmas using heptafluoroisopropyl methyl ether and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether

摘要

Heptafluoroisopropyl methyl ether (HFE-347mmy) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (HFE-347pcf2), whose global warming potentials are significantly lower than those of perfluorocompounds, are used for plasma etching of SiO2. The SiO2 etch rates are higher in the HFE-347mmy/Ar plasma than in the HFE-pcf2/Ar plasma owing to the larger production of CF2 radicals and corresponding formation of thicker fluorocarbon films on the substrate surface in the HFE-347pcf2/Ar plasma than in the HFE-347mmy/Ar plasma. The angular dependences of the etch rates at various bias voltages (-400 to -1200 V) are measured using a Faraday cage. The normalized etch yields (NEYs) have the maxima at ion incidence angles between 50 degrees and 60 degrees in both plasmas at all bias voltages. The NEYs increase with the bias voltage up to -800 V, and then virtually follow a single curve for bias voltages higher than -800 V in HFE-347mmy/Ar, while they continuously increase with the bias voltage in the range of -400 to -1200 V in HFE-347pcf2/Ar. The dependences of the NEYs of SiO2 on the ion incidence angle and bias voltage in both plasmas are explained by analyzing the thicknesses and fluorine-to-carbon ratios of the steady-state fluorocarbon films formed on the substrate surfaces.