Experimental Study on Radio Frequency Inductively Coupled Ar/NF$_3$ Discharges

We investigated the plasma parameters in radio frequency inductive Ar/NF$_3$ plasmas with the probe method and optical emission spectroscopy combined with actinometry. Plasma was produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 100 mm in length, and the power injected into the plasma was kept at 120W. Experiment was performed at three total pressures of 8m, 15m and 30 mTorr, changing the NF$_3$ content from 0$\%$ to 30$\%$. The structure of the measured electron energy probability functions (EEPFs) did not change at any NF$_3$ content, resulting in the same effective electron temperature. The measured EEPFs deviated from the Maxwellian distribution due to the large depletion of the electrons with the energy higher than 11-13 eV. On the other hand, the electron density markedly decreased even in small NF$_3$ addition lower than 5$\%$. The atomic fluorine density estimated by actinometry was approximately proportional to the NF$_3$ content. We investigated the effect of O$_2$ addition on the plasma parameters as well. The atomic fluorine density in Ar/NF$_3$/O$_2$ discharges depended on only NF$_3$ content. This fact may indicate that the reaction rate to produce the atomic fluorine by the collisions between the atomic oxygen and NF$_ {\rm x (x=1,2)}$ is much lower than that by the collisions between the atomic oxygen and CF$_{\rm x (x=2,3)}$. The atomic oxygen density was approximately proportional to O$_2$ content.