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

Abstract

Spatially resolved two-dimensional maps of the relative CF 2 density in low-pressure radio-frequency Ar/CF 4 /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% CF 4 , 1%-10% O 2 , 5-100 sccm, 3-35 W͒. Typically, the centerline (r ϭ 0) axial CF 2 distribution was symmetric with the local peak occurring near the center of the electrode gap, but, in all cases, significant radial variations in CF 2 density were observed ͑14%-45% standard deviation from the mean͒ 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 CF 2 density, while varying the composition, flow rate, and power primarily affected only the magnitude of the CF 2 density, with only modest changes in the spatial distribution. Based on image-averaged comparisons, the CF 2 density increased with power, pressure, and CF 4 mole fraction, decreased with addition of oxygen, and varied nonmonotonically with flow rate.

Surface Reactivity of CF2 Radicals Measured Using Laser-Induced Fluorescence and C2F6 Plasma Molecular Beams

“…First, there are significant differences in the gas-phase chemistry of CF 4 and C 2 F 6 FCPs. CF 4 plasmas have a higher density of F atoms (∼2:1) and a higher Si-etch rate, while C 2 F 6 plasmas have a higher density of CF 3 radicals. , Furthermore, CF 2 radicals are produced by different mechanisms in these FCPs …”

“…In contrast, CF 2 underwent partial decomposition on clean Si(100) substrates. Although CF 2 radicals have also been observed in various other FCPs, − , α values were not reported.…”

“…CF 2 radicals also help control the concentration of more reactive species such as F radicals, thereby influencing the balance between film deposition and etching in FCPs . To better understand the role of CF x radicals in FCPs, the gas-phase densities of CF x species have been measured using mass spectrometry of the effluent gas, , optical emission actinometry, laser-induced fluorescence (LIF), − and infrared absorption spectroscopy . In both CF 4 and C 2 F 6 plasmas, the CF 2 radical density is significant, which has lead many researchers to the conclusion that CF 2 contributes to FCP chemistry. , …”

Plasma non-uniformity in a symmetric radiofrequency capacitively-coupled reactor with dielectric side-wall: a two dimensional particle-in-cell/Monte Carlo collision simulation

“…Later experiments also showed that the argon metastable atom density peaked at this position, both in a pure argon discharge [19] and in argon mixtures with O 2 , Cl 2 , CF 4 [20]. McMillin and Zachariah observed peaks in the CF 2 density in an Ar/CF 4 discharge [21] using laser induced fluorescence imaging. During this time, 2D fluid models were developed by Boeuf and Pitchford [3] to reproduce the experimental results of Overzet and Hopkins [2], and the hybrid plasma equipment model [22] was able to reproduce the observations of McMillin and Zachariah [20].…”

Electrical control of plasma spatial uniformity investigated by planar laser-induced fluorescence

“…Current and voltage probes mounted on each electrode were used to determine electrical parameters, including , the 13.56 MHz amplitude of the current at the surface of the upper electrode. As described previously [1], [3], planar laser-induced fluorescence (PLIF) was used to determine twodimensional density maps of the reactive CF radical, and broadband spatially-resolved optical emission was utilized to indicate the regions of excited-state species formation. In PLIF, the 266 nm quadrupled Nd : YAG laser beam was expanded into a vertical sheet and passed through the GEC cell, where it electronically excited the CF from the X (0, 1, 0) ground state to the A (0, 2, 0) excited state.…”