Articles you may be interested inComparison of atmospheric-pressure helium and argon plasmas generated by capacitively coupled radiofrequency discharge Phys. Plasmas 13, 093503 (2006); 10.1063/1.2355428 Modeling of microcrystalline silicon film deposition in a capacitively coupled radio-frequency plasma reactor J. Appl. Phys. 97, 023308 (2005); 10.1063/1.1821639Electrostatic probe diagnostics of a planar-type radio-frequency inductively coupled oxygen plasma

In this paper, neutral and charged particle dynamics in both the capacitive and inductive modes of an inductively coupled oxygen discharge are presented. Langmuir probes, laser-assisted photodetachment and two-photon laser-induced fluorescence are employed to measure plasma parameters in the 13.56 MHz system for a range of plasma powers and gas pressures. It is found that the capacitive mode is more electronegative with lower molecular dissociation compared with the inductive mode. However, the negative ion density in each mode is comparable. A maximum is observed in the negative ion density and fraction with pressure for both modes. The experimental measurements are supplemented by a global model, which includes capacitive and inductive coupling effects. The model and experiments demonstrate that negative ion loss is dominated by ion-ion recombination and electron detachment at low pressures (<10 mTorr), while it is dominated by detachment processes with the metastable molecule O 2 (a 1 g ) and oxygen atoms at higher pressures. These findings support recent global model predictions of oxygen discharges.

We have investigated etching of deep (∼10 μm) submicron diameter holes with high aspect ratios (&gt;10) using plasmas maintained in mixtures of SF6 and O2 gases. The etching experiments were conducted in a low-pressure (5–80 mTorr), high-density, inductively coupled plasma etching reactor with a planar coil. We have studied the effects of pressure, rf-bias voltage, and SF6-to-O2 gas ratio on the etch rate, selectivity, and feature profile using Si wafers patterned with 0.35–0.5 μm diameter holes in a SiO2 mask. Visualization of the profiles with scanning electron microscopy is used in conjunction with plasma diagnostics such as optical emission and mass spectroscopies to understand the key factors that control the anisotropy, selectivity, and etch rate. The F-to-ion flux ratio and F-to-O flux ratio are found to be the important plasma parameters that determine the etch rate and anisotropy. Increasing the SF6-to-O2 ratio in the feed gas increases the F-to-O ratio in the plasma. At high SF6-to-O2 ratio, the mask undercut is severe because sidewall passivation by O atoms cannot keep up with the chemical etching by F atoms. As the F-to-O ratio is decreased, effective sidewall passivation by O atoms results in nearly vertical sidewalls. A further reduction in the F-to-O ratio results in sidewalls that slope inwards toward the bottom of the feature.

We have developed a semiempirical feature scale model of Si etching in SF6∕O2 plasma. The kinetic parameters in the model are determined by matching simulated profiles with experimentally observed feature profiles obtained at various pressures, rf-bias voltages, and O2 mole fraction in the feed gas. The model parameters are further constrained by using information about the relative radical concentrations, ion flux, and ion energy obtained from plasma diagnostics. Excellent agreement between experiments and simulations is obtained. The combined experimental and simulation study reveals that chemical etching in the lateral direction is significantly reduced through competitive adsorption of O on the feature sidewalls and subsequent formation of a fluorinated oxide layer that passivates the sidewalls. The flux of F and SFx radicals is focused toward the feature bottom due to increased neutral reflection off the passivated sidewalls. The net result is enhanced etching in the vertical direction and improved feature anisotropy with decreasing F-to-O ratio (increasing O2 fraction). However, too much O2 addition eventually leads to the slowing down of the vertical etch rate as O adsorption on active surface sites dominates even at the feature bottom.

Optical emission spectra from a low-pressure Ar plasma were studied with high spatial resolution. It has been shown that the intensity ratios of Ar lines excited through metastable levels to those excited directly from the ground state are sensitive to the shape of electron energy distribution function. From these measurements, important information on the spatial variation of plasma parameters can be obtained.