Two-dimensional imaging of CF2 density by laser-induced fluorescence in CF4 etching plasmas in the gaseous electronics conference reference cell

Spatially resolved two-dimensional maps of the relative CF2 density in low-pressure radio-frequency Ar/CF4/O-2 discharges generated within a parallel-plate Gaseous Electronics Conference reference cell have been obtained using planar laser-induced fluorescence imaging. The experiments cover a wide range of pressure, composition, flow rate, and power deposition conditions (13.3-133.3 Pa, 1%-100% CF4, 1%-10% O-2, 5-100 seem, 3-35 W). Typically, the centerline (r = 0) axial CF2 distribution was symmetric with the local peak occurring near the center of the electrode gap, but, in all cases, significant radial variations in CF2 density were observed (14%-45% standard deviation from the mean) with the peak density occurring near the edge of the discharge region. Varying the pressure led to significant changes in both the magnitude and spatial distribution of CF2 density, while varying the composition, flow rate, and power primarily affected only the magnitude of the CF2 density, with only modest changes in the spatial distribution. Based on image-averaged comparisons, the CF2 density increased with power, pressure, and CF4 mole fraction, decreased with addition of oxygen, and varied nonmonotonically with flow rate.