Modeling of fluorine-based high-density plasma etching of anisotropic silicon trenches with oxygen sidewall passivation J. Appl. Phys. 94, 6311 (2003); 10.1063/1.1621713Reduction of silicon recess caused by plasma oxidation during high-density plasma polysilicon gate etching Effects of gas distribution on polysilicon etch rate uniformity for a low pressure, high density plasma Evolution of etched profiles has been numerically studied during low-pressure, high-density ͑LPHD͒ plasma etching of Si in Cl 2 . The surface etch rates were calculated using a reaction model of synergism between incoming ions and neutral reactants, including the spread of ion angular distributions due to their thermal motions and the transport of neutrals arising from the reemission on surfaces in a microstructure. Etched profiles were then simulated using a so-called two-dimensional string algorithm to examine the effects of ion temperature kT i and energy ͑or sheath voltage͒ eV s on the etch anisotropy for different neutral-to-ion flux ratios ⌫ n /⌫ i toward the substrate. Numerical results indicated that in typical Cl 2 LPHD plasma etching environments, where the neutral-to-ion flux ratio is ⌫ n /⌫ i ϳ 1 and the ratio of sheath voltage to ion temperature is eV s /kT i ϳ 100, the chlorinated surface coverage is microscopically nonuniform in etched features: The coverage is very low at the bottom ͑␣ϳ0.1͒, whereas the sidewall surface ͑␣ϳ1͒ is almost saturated with neutrals. This microscopic nonuniformity of the coverage in etched features is the proposed mechanism responsible for the inversely tapered profiles that often occur in LPHD plasma etching. Additionally, the decrease in vertical etch rate in microstructures or the reactive-ion-etching lag due to neutral shadowing effects is also found to become significant in LPHD plasma etching. At such a low flux ratio of ⌫ n /⌫ i ϳ 1, more directional ions with a higher ratio of eV s /kT i տ 500 are required for the anisotropic etching; e.g., for an ion energy ͑or sheath voltage͒ of eV s ϭ 50 eV, the ion temperature in a plasma is required to be kT i Շ 0.1 eV.

Evolution of etched profiles has been numerically investigated during electron cyclotron resonance (ECR) Cl2/O2 plasma etching of polycrystalline Si. The calculations included the processes of chemically enhanced ion etching and passivation layer formation, which are important in such low-pressure, high-density plasma etching environments. The sidewall passivation was modeled by taking account of the redeposition of etch products on sidewalls of etched features. In addition, the effect of surface oxidation was also included in the model. Etched profiles were then simulated to examine effects of the neutral-to-ion flux ratio onto the substrate, sticking coefficient of etch products, and additional incident fluxes of etch products and oxygen atoms. Numerical results indicated that in typical ECR plasma etching environments, where the gas pressure is P0≲1 mTorr and the ion current density is Ji∼10 mA/cm2 onto the substrate, the chlorinated surface coverage α is microscopically nonuniform on sidewalls and bottom surfaces of etched features: α≲0.3 at the bottom and α≊1 on the sidewalls. This microscopic nonuniformity in coverage was found to lead to inversely tapered etched profiles without any sidewall passivation. These profiles changed to vertical and further tapered, when simultaneous redeposition of etch products were taken into account with their sticking coefficients Sp≳0.1. Furthermore, it was shown that in the presence of oxidation, the sidewall surfaces are easily oxidized, and the lateral etching is effectively reduced during overetch.

The advantages and feasibility of neutral beams with Z > 3 formed from negative ions, accelerated to 0.5-1.0 MeV-amu" 1 , and neutralized, are investigated for use in tandem mirror reactor end plugs. A reactor plasma physics design incorporating these beams has been done with the result that such a reactor could produce Q's (ratio of fusion power to injected power) of 20-30. These beams thus might be a replacement for the currently proposed 200-500-keV neutral proton beams presently planned for tandem mirror reactors. Thus these Z > 3 neutral beams could increase the potential attractiveness of tandem mirror reactors by offering a possible substitute for difficult high-energy neutral-hydrogen end plug beams.

Articles you may be interested inLow-pressure inductively coupled plasma etching of benzocyclobutene with SF6/O2 plasma chemistry J. Vac. Sci. Technol. B 30, 06FF06 (2012); 10.1116/1.4758765Reduction of silicon recess caused by plasma oxidation during high-density plasma polysilicon gate etching Level set approach to simulation of feature profile evolution in a high-density plasma-etching system Profile evolution during polysilicon gate etching has been investigated with low-pressure high-density Cl 2 /HBr/O 2 plasma chemistries. Etching was performed in electron cyclotron resonance Cl 2 /HBr/O 2 plasmas as a function of HBr percentage in a Cl 2 /HBr mixture, using oxide-masked poly-Si gate structures. The linewidth was nominally 0.18 m, and the spacing between the two neighboring poly-Si lines was varied in the range ϳ0.2-10 m. In addition, the macroscopic open space of the oxide-masked sample was also varied over a wide range from Ϸ28% to Ϸ76%. As the HBr percentage in Cl 2 /HBr is increased from 0 to 100%, the linewidth shift ⌬L of poly-Si relative to the mask width ͑or the degree of sidewall tapering of poly-Si lines͒ first decreased linearly, passed through a minimum, and then increased considerably at above ϳ80%. In Cl 2 /O 2 plasmas without HBr addition, ⌬L was almost independent of the microscopic and macroscopic poly-Si open spaces although its value was relatively large; on the contrary, in HBr/O 2 plasmas, ⌬L increased with an increase of microscopic line spacing and/or the macroscopic open space of the sample. Comparisons of the etched profiles obtained in Cl 2 /HBr/O 2 plasmas with numerical profile simulations indicate that the strongly tapered sidewalls observed at high HBr percentages ͑տ80%͒ result from the simultaneous etch inhibitor deposition onto sidewalls during etching; moreover, such inhibitors are predicted to come from the plasma with a large sticking probability of ϳO(0.1). On the other hand, the relatively large ⌬L obtained in Cl 2 /O 2 plasmas is considered to be due to intrinsic sidewall tapering, rather than inhibitor deposition arriving from the plasma or redeposition of etch products desorbed from the surface in microstructures. Such intrinsic tapering is discussed in terms of the angular dependence of the Si etch yield.

Articles you may be interested inAbsolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging J. Appl. Phys. 85, 696 (1999); 10.1063/1.369149Laserinduced dissociation of molecules during measurements of hydrogen atoms in processing plasmas using twophoton laserinduced fluorescence Atomic chlorine concentrations in Cl z plasmas have been measured by two-photon laser-induced fluorescence (LIF). Experiments were performed over a wide pressure range in rf, rfmagnetron, and microwave electron cyclotron resonance (ECR) discharges. Absolute calibration was achieved by generating CI atoms through UV photolysis of CCI 4 with the same laser radiation. The LIF measurements showed that in the respective discharges, the CI concentrations decreased and the corresponding CI fractions increased with decreasing pressure: the measured fractions ranged from 0.3% to 0.7% in rf discharges, from 0.8% to 8% in magnetron, and from I % to 2% in ECR. These results, together with electrical measurements of ion and electron energies and densities, demonstrated that the ratio of neutral CI flux to ion flux toward the substrate decreased from 400: 1 to 1: 1, almost linearly with decreasing pressure in the three discharges. These results of plasma diagnostics are compared with the etching characteristics of heavily P-doped polycrystalline Si obtained.