Addition Of SF6 Research Articles

Effects of SF6 Addition to O2 Plasma on Polyimide Etching

For further scaling down of silicon devices, the application of low-k interlayer dielectrics instead of silicon oxide has been considered to reduce power consumption, crosstalk and interconnection delay. In this paper, the effect of SF6/O2 plasma chemistry on the etching characteristics of polyimide has been studied using a electron cyclotron resonance (ECR) plasma etching system. Addition of SF6 gas results in a very smooth etched surface even though this causes a reduced etch rate due to the formation of nonvolatile fluorine compounds inhibiting the reaction between oxygen and hydrocarbon polymers. However, the etch rate can be compensated by applying a substrate bias or increasing the microwave power. As a result, 1–2 µm line and space patterns were successfully obtained using a SiO2 hard mask.

Mass spectrometric characterization of BCl3/SF6 plasmas

Significant increases in the etch rates of both GaAs and GaN have been observed with the addition of SF6 to BCl3 plasmas. Mass spectrometric characterization of neutrals in these gas mixtures shows that increasing the SF6 percentage in the flow enhances the dissociation of BCl3, resulting in nearly 100% dissociation at 70% SF6. This increased dissociation is believed to be due to electron attachment heating. Both Cl and Cl2 mass intensities also maximize at 70% SF6. The detection of BClF and BCl2F suggest the possibility of reactions occurring between BCl and BCl2 radicals and fluorine, which may inhibit the recombination of Cl.

Influence of the H2and SF6addition to Ne + 1%Xe on the narrow barrier discharge spectral radiation

The experimental results concerning the modification of the NeI emission spectra as well as the time evolution of both the discharge current and the yellow line intensity with the wavelength of 585.3 nm, at the H2 and/or SF6 addition to the Ne+1%Xe Penning mixture, are obtained for the narrow gap dielectric barrier discharges. The H2 and SF6 contribution to the depletion of the lower level 1s2 through Penning collisions and also the hydrogen participation to the feeding of the upper level 2p1 of the optical transition 2p1−1s2 of the neon have been revealed.

Effects of O2 and SF6 on CH4 Plasma CVD Film.

CH4 plasma CVD films were formed by a reactor with a parallel plate electrode system at a discharge frequency of 13.56MHz with using a mixture gas of CH4/H2 and H4/Ar. The deposition rates were measured as a parameter of gas pressure, and discharge power in order to discuss deposition mechanisms. The effects of O2 and SF6 addition in the mixture gases were also examined. Addition of oxygen gas in the mixture gas of CH4/H2 enhanced the growth rates, which were proportional to the radiation intensity ratio CH/Hα in the plasma. On the other hand, the addition of oxygen gas in the mixture gas of CH4/Ar decreased the growth rate. It was observed that oxygen atoms were extracted from the film during the process, however sulfur atoms were doped into the film. These experiments suggested the possibility of film property control.

Si nanostructures fabricated by electron beam lithography combined with image reversal process using electron cyclotron resonance plasma oxidation

A new image reversal process has been developed for Si nanodevice fabrication that uses electron beam lithography and electron cyclotron resonance (ECR) plasma techniques. This process is based on Si oxidation with an ECR oxygen plasma through the openings in resist mask patterns. Si on SiO2 is selectively etched by either Cl2-based ECR plasma etching or KOH anisotropic etching by using a plasma oxide mask. ECR plasma formed silicon oxide with a thickness of 2–3 nm was found to be an excellent etch mask for these etching techniques. Highly directional ECR oxygen plasma keeps the change in the resist linewidth and edge roughness small enough for nanofabrication. Furthermore, the linewidth of reversed Si patterns can be reduced by SF6 addition to Cl2 in ECR plasma etching. This image reversal process successfully achieves 10-nm-scale Si wires and pillars.

Dry patterning of InGaN and InAlN

Dry etch rates of InxGa1−xN and InxAl1−xN alloys are found to increase with In mole fraction in CH4/H2 microwave (2.45 GHz) discharges, and to decrease under the same conditions in Cl2/H2 mixtures. Both plasma chemistries produce smooth anisotropic etching across the entire composition range from InN to either GaN or AlN. Addition of SF6, rather than H2, to a Cl2 discharge produces faster etch rates and retains smooth morphologies. This suggests that either atomic hydrogen or fluorine is capable of effective removal of N from the III-V nitride materials. Ar+ ion milling rates for InGaAlN alloys are found to be approximately a factor of 2 lower than for more conventional III-V semiconductors like GaAs.

Nitrogen laser employing twin sliding discharges

Twin sliding discharges are used in an ultraviolet nitrogen laser as a direct excitation mechanism as well as a preionizer at the same time. Addition of SF6 is found to cause the appearance of a volume discharge between the two sliding discharges and an increase of the laser output energy by a factor of 9. Under optimum conditions a pulse energy as high as 3.1 mJ from a 16 cm3 active volume is achieved. Investigations of the temporal behavior and the spatial properties of the laser output are presented.

Electronic state distributions of Kr+* formed by excitation transfer from He(2 3S) to Kr+(2P3/2) and Kr+(2P1/2) at thermal energy

The He(2 3S)+Kr+(4p5 2P3/2,1/20) excitation-transfer reaction has been studied by observing ultraviolet (UV) and visible emissions from Kr+* in the He flowing afterglow. The relative contribution of Kr+(2P3/20) and Kr+(2P1/20) to the excitation of Kr+* was examined by changing the [Kr+(2P1/20)]/[Kr+(2P3/20)] ratio with the addition of SF6 as a remover of the lower spin–orbit component. The He(2 3S)+Kr+(2P3/20) reaction gives 13 Kr+(5p,5p′,6s) levels in the 16.60–19.58 eV range, while the He(2 3S)+Kr+(2P1/20) reaction populates 26 Kr+(5p,5p′,5d,6s,6s″) levels in the 16.60–20.47 eV range. The electronic state distributions of individual Kr+* levels have been determined by taking account of radiative cascade for low lying electronic levels. The favored product levels are the 6s 4P5/2 level at 19.48 eV for both reactions. Since these product channels are 0.34 and 1.00 eV below the entrance channels, attractive entrance potentials are probably important. The total formation rate of Kr+* in the He(2 3S)+Kr+(2P1/20) reaction is larger than that in the He(2 3S)+Kr+(2P3/20) reaction by a factor of 2.4. No evidence of the formation of Kr+* by the He++Kr(3P2,00) charge-transfer reaction is found.

Dry etching characteristics of III?V semiconductors in microwave BCl3 discharges

Electron cyclotron resonance (ECR) BCl3 discharges with additional rf biasing of the sample position have been used to etch a variety of III–V semiconductors. GaAs and AlxGa1−xAs (x = 0−1) etch at equal rates in BCl3 or BCl3/Ar discharges, whereas SF6 addition produces high selectivities for etching GaAs over AlGaAs. These selectivities are in excess of 600 for dc biases of ≤−150 V, and fall to ≤6 for biases of −300 V. If the dc biases are kept to ≤ − 100 V, there is no measurable degradation of the optical properties of the GaAs and AlGaAs. The AlF3 formed on the AlGaAs surface during exposure to BCl3/SF6 plasmas can be removed by sequential rinsing in dilute NH4OH and water. In-based materials (InP, InAs, InSb, InGaAs) etch at slow rates with relatively rough morphologies in BCl3 plasmas.

Dissociative excitation of CF4, CCl4, and chlorofluoromethanes by collisions with argon and helium active species

Dissociative excitation of CFnCl4–n (n=0–4) by collisions with Ar and He active species has been studied by observing uv and visible emissions in the Ar and He afterglows. Emissions from such excited fragments as Cl*, Cl*2, CF*, CCl*, CCl+*, ArCl*, CF*2, CCl*2, CFCl*, and CF*3 were observed. New continuous bands which may be related to Cl*2, CFCl*, CCl*n(n=2,3), and CCl+*n(n=2,3) were found in the reactions of CFCl3 and CCl4. The effects of ion trapping and SF6 addition into the discharge flow indicated that the excited species were produced from primary reactions by the metastable Ar(3P2) and He(2 3S) atoms and (Ar+)* and He+ ions and/or secondary reactions via electron–ion recombination processes. The emission rate constants have been determined for the primary reactions of Ar(3P2), He(2 3S), and He+ with CFnCl4–n (n=0–3). A comparison between the observed emission rate constants and known total quenching rate constants indicated that dissociative excitation processes are minor exit channels (≤4.6%).

Comparison of mechanistic model with experimental observation: The Ar(2p2)→Ar(1s4) emission signal in the pulse radiolysis of argon

The temporal behavior of atomic and molecular ions and of several classes of neutral states lying above the Ar(1s) manifold has been mathematically modeled in a successful attempt to reproduce observed Ar(2p2)–Ar(1s4) emission signals at 296 K with Ar pressures in the 100–200 Torr region. In addition, traces of SF6 were added to remove the effects of the slow electron thermalization associative ionization cycle characteristic of pure Ar. The proposed model mechanism necessarily includes additional reaction steps required by the addition of SF6. Good agreement was obtained between observed and calculated emission profiles only after the introduction of Ar+2 as an important thermalizer of fast electrons in pure Ar. Previously published rate constant values for the various elementary steps assumed to comprise a simplest probable mechanism were found to be generally acceptable.

Formation of CH(A 2Δ,B 2Σ−,C 2Σ+) by electron–ion recombination processes in the argon and krypton afterglow reactions of CH4

The CH(A–X,B–X,C–X) emission systems have been observed from the Ar and Kr afterglow reactions of CH4. A significant attenuation of the CH(A–X,B–X,C–X) emissions by an addition of SF6 into the discharge flow suggested that the CH(A,B,C) radicals are excited via secondary electron–ion recombination processes. Since the CH(A–X,B–X,C–X) emissions disappeared by trapping ionic active species in the discharge flow, the responsible active species for the CH(A,B,C) production were found to be Ar+ and/or (Ar+)* in the Ar flow and Kr+ and/or (Kr+)* in the Kr flow. The contribution of Ar+ and Kr+ was examined in the He afterglow, where Ar+ or Kr+ and slow electrons were simultaneously produced by the He(23S)/Ar,Kr Penning ionization. Although intense CH(A–X,B–X,C–X) emissions were observed from Ar+/CH4 where CH+n(n=2–4) were formed, they were absent from Kr+/CH4 where only CH+4 was produced. It was, therefore, concluded that CH+2 and/or CH+3 are important precursor ions for the CH(A,B,C) production. The intensity distribution of CH(A,B,C) and the CH(A,B) rovibrational distributions obtained in the Ar afterglow agreed with those through Ar+/CH4, indicating that Ar+/CH4 plays a significant role for the production of precursor ions in the Ar afterglow or (Ar+)*/CH4 provides the same precursor ions. Since the relative intensity of CH(A,B) and the rovibrational distributions of CH(A) in the Kr afterglow were different from those in the Ar afterglow, different electron–ion recombination processes dominantly take part in the CH(A,B) production.

Oxygen atom actinometry reinvestigated: Comparison with absolute measurements by resonance absorption at 130 nm

Resonance absorption at 130 nm was used to measure absolute oxygen atom concentrations in O2-containing distributed electron cyclotron resonance plasmas. The dissociation fraction [O]/[O2] in pure O2 plasmas (1–6 mTorr) was in the range 0.01–0.06, but was significantly increased by the addition of SF6, N2 or Kr. At 2 mTorr total pressure a maximum [O]/[O2] of 0.3 was observed for 10% SF6 added. The results were compared to those obtained by optical emission actinometry measurements. The quantity I0 (844 nm)/IAr (750 nm) (with 0.1 mTorr Ar added) was poorly correlated with [O] but well correlated with [O2]. This suggests that, for dissociation fractions lower than 0.1, dissociative excitation, O2+e→O*(3p 3P)+O, is the most important mechanism for the production of 844 nm emission.

Dissociative excitation of CH4 by collisions with helium active species

Dissociative excitation of CH4 by collisions with He(2 3S), He+, and He+2 has been studied by observing CH(A 2Δ–X 2Πr, B 2Σ−–X 2Πr, and C 2Σ+–X 2Πr) and H (Balmer) emissions in the flowing afterglow and beam apparatus. The effect of SF6 addition into the He afterglow indicated that the formation of CH(A,B,C) in the flowing afterglow proceeds through both the primary He(2 3S)/CH4 reaction and a secondary electron–ion recombination reaction through the He+/CH4 and/or He+2/CH4 reactions. The emission rate constants of A–X, B–X, and C–X of CH, Hα, and Hβ produced from the He(2 3S)/CH4 reaction were determined to be 5.6, 1.5, 0.011, 0.46, and 0.072×10−13 cm3 s−1 in the beam experiment, respectively. The nascent vibrational distribution of CH(A) from He(2 3S)/CH4 was determined as N0:N1=100:37±5. The rotational distributions were expressed by single Boltzmann temperatures of 3200±200 and 2600±300 K for v′=0,1 of CH(A) and 3300±200 K for v′=0 of CH(B).

Dissociative excitation of GeH4 by collisions with Ar and He active species

The product channels in reactions of metastable Ar(3P2) and He(23S) atoms and Ar+, (Ar+)*, He+, and He+2 ions with GeH4 have been studied by observing emission spectra in the flowing afterglow and beam apparatus. H*, Ge*, GeH(A 2Δ–X 2Π), and GeH+(a 3Π0+,1–X 1Σ+) emissions were observed in the 190–600 nm region. The effect of SF6 addition into the discharge flow indicated that secondary electron-ion recombination processes participate in the formation of Ge* and GeH(A) in the Ar and He afterglows. The formation of Ge* through the Ar+/GeH4 reaction followed by electron-ion recombination processes was confirmed by simultaneous formation of Ar+ and low-energy electrons through the He(2 3S)/Ar Penning ionization. The total emission rate constants were determined to be 8.6 and 0.15×10−12 cm3 s−1 for Ge* and GeH(A) in the Ar(3P2)/GeH4 reaction, and 0.068 and 5.8×10−12 cm3 s−1 and for H* and Ge* in the He(2 3S)/GeH4 reaction, respectively.

Selective dry etching of InGaAs and InP over AlInAs in CH4/H2/SF6

The addition of SF6 to CH4/H2 discharges is shown to produce a significant increase in the selectivity for dry etching of both InGaAs and InP over AlInAs. The selectivity is a strong function of the dc bias on the sample during the reactive ion etching, with equirate removal of InGaAs and AlInAs for biases above 300 V. For lower bias values, the etch stop mechanism is related to the formation of Al-F and In-F species on the AlInAs surface, as evidenced by x-ray photoelectron spectroscopy. The use of SF6 allows independent variation of the ratio of F to the other reactive species, in comparison to the use of fixed ratio gases such as C2H4F2 or CH3F.

Influence of SF6on the energy characteristics of an H2–F2chemical laser

A model of a hydrogen fluoride laser taking into account the finite rate of rotational relaxation is used to study the influence of the addition of SF6 to the mixture on the energy characteristics of a pulsed H2–F2 chemical laser. A comparison between the results of the calculations and the experimental data suggests that an increase in the laser energy with increasing SF6 concentration in the active mixture is largely due to a rise in the rate of rotational relaxation of the HF molecules. It is shown that a drop in the specific laser output energy at very high SF6 concentrations is not only due to an increase in the rate of vibrational–rotational relaxation, but also to the influence of the resonator threshold on the laser energy characteristics as a result of the appreciable broadening of the HF vibrational–rotational lines.

Ozone Formation from the Reaction Of O2-Activated N2Molecules and a New Type of Ozone Generator with Fine Wire Electrode

Abstract Experiments using an ozone generator which has a fine steel wire electrode are described. Various conditions of the wire electrode ozone generator such as wire diameter, volume density of wire electrode, applied voltage and the effects of SF6 addition also are reported. The efficiency of the wire electrode ozone generator in air exceeded that of the usual ozone generator for 0.1 mm wire diameter and 0.156 g cm−3 volume density of wire over the entire range of applied voltage. This efficiency increases by adding 0.08% SF6 in air. Increase of ozone and NOX formation in the air ozone generator can be explained by the reactions of O2 and activated N2.

Characteristics Of An Ultraviolet Preionized High Power Nitrogen Laser

The effect of UV preionization in a discharge-excited high power nitrogen laser is presented. A maximum energy of 7.7 mJ in a 4.7 ns pulse is reported for the case of a N2/He mixture. An increase of the output energy by 65% with the addition of SF6, an electron quencher, is also observed.

Ozone synthesis in charged particle induced noble gas-oxygen and noble gas-oxygen-sulfur hexafluoride discharges

A series of experimental measurements of ozone concentration produced by irradiation of noble gas (He, Ne, and Ar)-O2 and noble gas-O2-SF6 mixtures with energetic (MeV) helium and lithium ions are reported. Continuous irradiations at dose rates of 1015–1017 eV cm −3 s −1 for a few hundred milliseconds were used. The resulting ozone concentration was found to be nonlinear with dose rate for a given irradiation time. This nonlinearity was effectively reduced by an increase in noble gas pressure. Few mole percent addition of SF6 generally resulted in an increase in the ozone concentration. This increase was highest for lower noble gas pressures and longer irradiation times. Further SF6 addition, however, caused a reduction in the ozone concentration. Results are explained by considering the relevant reactions responsible for ozone production and loss.