CF and CF2 actinometry in a CF4/Ar plasma

Abstract

Relative ground state CF and CF₂ concentrations have been measured in a 13.56‐MHz rf CF₄/Ar discharge using both laser‐induced fluorescence (LIF) and actinometric techniques to assess the validity of actinometry for CF and CF₂ over a limited parameter space of pressure and power. Relative measurements of the CF ( A²Σ − X²Π) system and the CF₂ ( A¹B₁ − X¹A₁) system were made by LIF. Actinometric values were calculated from relative measures of the plasma‐induced emission (PIE) intensity of the CF* ( B²Δ− X²Π) at 202.4 nm, CF₂^* ( A¹B₁ − X¹A₁) at 251.9 nm, and Ar* [4s’(1/2)°−4p’(1/2)] at 750.4 nm. Both LIF and PIE signals were spatially averaged over the bulk of the plasma. Steady‐state actinometric and LIF measurements were compared for CF₄/5% Ar discharges at pressures in the range of 500 to 1000 mTorr and nominal powers in the range of 20 to 100 W. Dynamic actinometric and LIF measurements of CF were made by modulating the discharge power and monitoring the CF transient at one set of conditions, 500‐mTorr pressure and 70‐W nominal power. Our results indicate that actinometric measurements of CF and CF₂ correlate well with relative CF and CF₂ LIF measurements under the studied conditions.