Comparison of Plasma Parameters Measured in Inductively Coupled Ar/C4F8/O2 and Ar/CF4/O2 Plasmas

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The properties of inductively coupled Ar/C4F8/O2 and Ar/CF4/O2 plasmas are investigated at two total pressures of 15 and 30 mTorr. Measurements using a Langmuir probe and optical emission spectroscopy are carried out, while varying the ratio of the oxygen fraction to the sum of fluorocarbon and oxygen fractions ($R_{\text{OC}}$) at an Ar fraction higher than 70%. The measured electron energy probability functions slightly deviate from the Maxwellian distribution owing to the depletion of electrons with an energy higher than 10 eV. The electron density measured in the Ar/C4F8/O2 plasmas gradually decreases with increasing $R_{\text{OC}}$ and reaches a minimum at $R_{\text{OC}}\approx 0.3$, whereas that in the Ar/CF4/O2 plasmas does not strongly depend on $R_{\text{OC}}$. The density of CF2 radicals in the Ar/C4F8/O2 plasmas markedly decreases in the range of $0.2\leq R_{\text{OC}}\leq 0.4$, whereas that of oxygen atoms in the Ar/C4F8/O2 plasmas more sharply increases with increasing $R_{\text{OC}}$ compared with that of oxygen atoms in the Ar/CF4/O2 plasmas. The density of fluorine atoms measured in the Ar/C4F8/O2 plasmas reaches a minimum at $R_{\text{OC}}\approx 0.3--0.4$ and then starts to increase again, whereas that in the Ar/CF4/O2 plasmas has a maximum at $R_{\text{OC}}\approx 0.2--0.3$.
2009-09-25