We have investigated etching of deep (∼10 μm) submicron diameter holes with high aspect ratios (>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.
Simulation results and experimental measurements in an oxygen ICP are used to examine transport and reaction in oxygen inductively coupled plasmas. The trends of plasma characteristics with pressure and rf power are considered. We show that the balance between gas phase O2 dissociation and surface O recombination controls the plasma characteristics under the investigated conditions. Neutral density profiles are primarily the result of diffusive transport in balance with fast surface reactions. According to the model, the O(1D), O2(a1Δ), and O2(b1Σ) metastable states play an important role in dissociation, ionization, and attachment kinetics. The O(1S) metastable is not kinetically important.
This article reports a simulation of argon inductively coupled plasma. Experimental measurements of the electron energy distribution function (EEDF) are fit to a power-law model and used to calculate electron impact rate coefficients in the simulation. Simulation results are compared to experimental measurements of electron density and temperature with good agreement, especially at the lower pressures investigated. At higher pressures, the disagreement between experiment and model is analyzed in terms of the nonlocality of the EEDF. Diffusive transport, neutral heating, gas phase electron impact reactions, and surface quenching all contribute to the predicted metastable profiles. Predicted metastable densities and neutral gas temperatures are compared to experimental results from the literature with reasonable agreement.
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.
Articles you may be interested inCompensation for transient chamber wall condition using real-time plasma density feedback control in an inductively coupled plasma etcher Inductively coupled, point-of-use plasma abatement of perfluorinated compounds and hydrofluorinated compounds from etch processes utilizing O 2 and H 2 O as additive gases Point-of-use plasma abatement ͑PPA͒ has been proposed as one way to eliminate perfluorinated compound ͑PFC͒ emission from various tools used in integrated circuit manufacturing. PPA employs a high density plasma between the process tool turbomolecular pump and the backing pump. Oxygen is added to the process tool effluent upstream of the PPA tool. The mixture of oxygen and PFC-containing tool effluent enters the PPA tool and the PFCs are converted to products that can be scrubbed downstream of the backing pump. In this article, we present a model for the PPA tool operation, illustrating the principles with a mixture of C 2 F 6 /O 2 . A plasma model is coupled to a neutral transport and reaction model, including electron-impact molecular dissociation and subsequent gas phase chemistry.
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