Ar Ratio Research Articles

Trench etch processes for dual damascene patterning of low-k dielectrics

The use of dual damascene patterning for integration of Cu with low-k dielectric films has introduced new challenges for plasma etch processes. With a via-first dual damascene approach, an important issue for trench etch is defect formation (i.e., oxide ridges) around vias which can degrade device reliability. The use of low-k films as the dielectric material adds additional complexity and more limitation on the etch process parameters. This article discusses the development of etch processes that meet the special requirements for Cu/low-k dual damascene trench etch. All experiments were conducted in a medium-density TEL dipole ring magnet system. The dielectric film used here was an organosilicate glass (OSG). Using C4F8/N2/Ar chemistry, a trade-off was observed between etch rate and oxide ridge formation. The N2:Ar ratio was found to be the key parameter in controlling the severity of the oxide ridges, but eliminating the ridges using the N2:Ar ratio resulted in a low OSG etch rate and poor throughput. However, we found an alternative method which achieves a high OSG etch rate while maintaining critical dimension control and ridge-free conditions. The effect of various process parameters on the OSG etch rate and ridge formation is detailed. A comparison of experimental results against numerical simulations of C4F8-based bulk plasmas with varying gas flow ratios is also reported.

Effects of nitrogen fraction on the structure of amorphous silicon–carbon–nitrogen alloys

The silicon–carbon–nitrogen (SiCN) alloys prepared by DC magnetron sputtering at room temperature with graphite and silicon targets at different nitrogen partial pressure were systematically investigated. It was found that a high nitrogen fraction in the nitrogen–argon gaseous mixture enhances the incorporation of C and N, but reduces the incorporation of Si. The SiC, SiN, SiSi, CN, CN, CN, CO, CC, CC and NH bonds can all be observed in the alloys. The CN, CC and CN bonds dominate the structure of the alloys, while the SiC, SiSi and SiN bonds are less significant. As the N 2/(N 2+Ar) ratio increases, the densities of the SiC, SiN and CN bonds decrease, while those of the CN, CC, CC and CN bonds increase. In addition, the deposition rate is found to monotonically increase with the nitrogen partial pressure, probably due to the enhanced incorporation of nitrogen and carbon.

Identification of H2O·HO in Argon Matrices

The infrared spectrum of OH in Ar matrices at temperatures of 11.5 ± 0.5 K has been investigated as a function of water concentration for H2O:Ar ratios ranging from 1:70 to 1:1000. These data and evidence gathered from earlier experimental and theoretical work lead to an assignment of bands at 3452 and 3428 cm-1 to the H2O·HO complex. This is the first time that a definitive assignment has been made to an isolated H2O·HO complex. This observation may have important implications for fields as diverse as molecular biology, astrochemistry, atmospheric chemistry, and electrochemistry.

Primordial noble gases in “phase Q” in carbonaceous and ordinary chondrites studied by closed‐system stepped etching

Abstract— The HF/HCI‐resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed‐system stepped etching (CSSE) in order to better characterise the noble gases in “phase Q”, a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (20Ne/22Ne)Q. As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991, 1992), (20Ne/22Ne)Q is the least uniform isotopic ratio of the Q noble gases. The data cluster ∼10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (20Ne/22Ne)Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar‐Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne‐Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases “Q1” and “Q2” with slightly distinct chemical properties. Ratios (Ar/Xe)Q and (Kr/Xe)Q reflect both thermal metamorphism and aqueous alteration. These parent‐body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)Q and (Ne/Ar)Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q2. Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q1 and Q2 must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q1 may be related to presolar graphite. Phases Q1 and Q2 might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the 20Ne/22Ne ratios cannot be attributed to the carriers Q1 and Q2. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne‐E(L), and the data confirm the suggestion of Huss (1997) that the 22Ne‐E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.

Dielectric characterization of microwave plasma enhanced chemical vapor deposition diamond films with Ar–H2–CH4 gas mixture

Dielectric properties of diamond films grown by microwave plasma enhanced chemical vapor deposition (MPECVD) on tungsten carbide (WC) substrates from Ar–H 2 –CH 4 gas mixture were studied using an impedance analyzer. The dielectric dispersion is observed in the frequency range from 100 Hz to 15 MHz. The real and imaginary parts of impedance of diamond films deposited at the different Ar ratios of the reactive gases consist of a semicircle in the complex plane and can be fitted to the theoretical circuit model. The frequency dependence of the imaginary part of the impedance implies different time constants τ, which are closely related to the diamond film’s AC resistivity ρ and dielectric constant ε. The values of the resistivity of diamond films increase with increasing Ar gas ratio, which is an indication of lower graphite content of the samples with higher Ar gas ratio. Raman spectroscopy also confirmed the results. It is found that Ar ions in a microwave plasma possess the ability to remove the unexpected non-diamond phases and improve the diamond quality.

GROUND EFFECT OF FLOW AROUND AN ELLIPTIC CYLINDER IN A TURBULENT BOUNDARY LAYER

The flow characteristics around an elliptic cylinder with an axis ratio of AR=2 located near a flat plate were investigated experimentally. The elliptic cylinder was embedded in a turbulent boundary layer whose thickness is larger than the cylinder height. For comparison, the same experiment was carried out for a circular cylinder having the same vertical height. The Reynolds number based on the height of the cylinder cross-section was 14000. The pressure distributions on the cylinder surface and on the flat plate were measured for various gap distances between the cylinder and the plate. The wake velocity profiles behind the cylinder were measured using hot-wire anemometry. In the near-wake region, the vortices are shed regularly only when the gap ratio is greater than the critical value of G/B=0·4. The critical gap ratio is larger than that of a circular cylinder. The variation of surface pressure distributions on the elliptic cylinder with respect to the gap ratio is much smaller than that on the circular cylinder. This trend is more evident on the upper surface than the lower one. The surface pressures on the flat plate recover faster than those for the case of the circular cylinder at downstream locations. As the gap ratio increases, the drag coefficient of the cylinder itself increases, but the lift coefficient decreases. For all gap ratios tested in this study, the drag coefficient of the elliptic cylinder is about half that of the circular cylinder. The ground effect of the cylinder at small gap ratio constrains the flow passing through the gap, and restricts the vortex shedding from the cylinder, especially in the lower side of the cylinder wake. This constraint effect is more severe for the elliptic cylinder, compared to the circular cylinder. The wake region behind the elliptic cylinder is relatively small and the velocity profiles tend to approach rapidly to those of a flat plate boundary layer

A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide

A synergetic effect is found in the sonochemical formation of HNO2 in HNO3 solution in the presence of an N2O–Ar gaseous mixture. The maximum rate of HNO2 formation is observed at an N2O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO3 solutions, the rate of HNO2 formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N2O.

The Getafe rock: Fall, composition and cosmic ray records of an unusual ultrarefractory scoriaceous material

In 1994 a moving car and its driver, on a highway in southern Madrid (Getafe), were struck by a falling rock. Eighty-one additional fragments (total weight: 55.926 kg) were later recovered, which all pointed towards a meteorite fall. A study of the composition of this object revealed an ultrarefractory material displaying a most unusual chemical make-up which differs from any known meteorite class, and for some elements and minerals approaches the composition of CAI (Ca-Al-rich inclusions in chondrites). A study of some cosmic-ray-produced stable and radioactive nuclides indicates: a) space and terrestrial exposure ages which do not exceed 1,000 and 520,000 years, respectively; b) the presence of a small 22 Ne excess (1,100°C fraction), which suggests either a nucleogenic contribution from the 19 F(α,n) 22 Ne reaction or a trapped Ne signature distinct from atmospheric Ne, and c) the existence of minor variations in the 38 Ar/ 36 Ar ratios also indicating a nucleogenic component or fractionation effects. 14 C data are consistent with modern carbon originated in the period 1955-1958 and not earlier or more recently. The possibility that the Getafe rock could have a man-made origin (i.e. ceramic and refractory tiles, industrial slag) is also considered.

Single-crystalline-like La2-xSrxCuO4 thin films and their transport properties

c-axis oriented La2-xSrxCuO4 films have been prepared by the dc magnetron sputtering method. Smooth surface morphology and excellent crystallinity of the films are observed by SEM and TEM, respectively. It was found that the zero resistance temperature Tc0 and the lattice parameter of the films are strongly dependent on Sr content and oxygen partial pressure of the sputtering gas. Increasing the O2:Ar ratio can remedy the oxygen deficiency and improve the superconductivity of the films.

Neon excess in pumice: volcanological implications

We measured the noble gas abundance and Ne and Ar isotopic compositions in pumice samples from Japan and the Eolian Islands, Italy. The goal was to give clues on the mechanism of air incorporation into pumice and its relationship with eruption processes. The samples contain large excesses of atmospheric Ne over Ar, with 20 Ne/ 36 Ar ratios up to 600 times the atmospheric ratio. This excess is produced by the preferential diffusion of Ne over Ar in pumice vesicles during volcanic eruptions. The 20 Ne/ 36 Ar ratios measured in pumice reflect the initial quenching temperature, the cooling rate of the eruption column and the bubble's wall thickness. The final Ne amount is likely to be proportional to the volume of preserved vesicles in pumice. Calculations indicate that the fraction of isolated vesicles are less than 10% of the total, suggesting that a few amount of gas is preserved in pumice after deposition.

Tribological characteristics of SiN/sub x/ films

The tribological performance and chemical compositions of thick (75 nm-120 nm) amorphous SiN/sub x/ films are studied with CSS testers and XPS. A high-speed H/D contact program is used to provide intermittent head/disc contacts. Films with high Si/N ratio (1.25) and high oxygen concentration (22%) have the best durability. Films' durability is also affected by the sputtering conditions used to prepare films. A higher N/sub 2//Ar ratio will produce a lower durability film. The film durability is not sensitive to the total pressure and sputtering power in the range of 5-15 mTorr and 1-4 kWatt.

Effects of wall recombination on the etch rate and plasma composition of an etch reactor

A helicon plasma etch reactor is simulated using direct simulation Monte Carlo and particle-in-cell methods for a chlorine (Cl2) feed gas flow. Computations for the gas discharge are carried out by modeling the ions and neutrals as particles and by imposing the electrons as a background condition conforming to experimental measurements. The neutrals and ions are then allowed to interact with the background electrons and to relax to a steady state. The effects on the reactor flow field and etch rate of chlorine atom recombination into chlorine molecules at the walls is investigated. Results show that recombination at the walls results in the depletion of the amount of chlorine atoms (Cl) in the reactor. The depleted chlorine atom population leads to lower ionization levels and a diminished ion (Cl+) flux to the wafer. Consequently, the etch rate is decreased by as much as 15% when compared to simulations without recombination. The creation of chlorine (Cl2) molecules at the walls through recombination also provides a new source for negative ions (Cl−) which increases the electronegativity of the plasma. In addition, the results of the simulation are compared with ion current and optical emission spectroscopy (OES) measurements. The Cl–Ar ratio (measured by the OES technique) increases less than 20% from the centerline to the wall of the reactor. An inspection of absolute densities, however, reveals that the individual near-wall densities are as much as a factor of 2 greater than the centerline densities. The trace species, Ar, therefore, does not become distributed evenly throughout the reactor.

NOBLE GASES IN THE EARTH'S MANTLE

▪ Abstract Noble gas isotopic ratios in mantle-derived samples require variability in the time-integrated ratio of volatile to lithophile elements in the Earth. Documentation of mantle 3He/4He variability is becoming increasingly complete, but for the heavier noble gases, the picture is still partly clouded by the effects of atmospheric contamination of mantle samples. Nevertheless, clear variations in mantle Ne, Ar, and Xe isotopic ratios exist, are apparently correlated with 3He/4He, and may be the product of varying degrees of mantle degassing. However, uncertainties in noble gas geochemical behavior and several conflicting observations leave open other possibilities. Recent Ne isotopic data are particularly important because they require that the atmosphere has not been closed to exchange with space. Derivation of much of the atmosphere from a source other than degassing of the mantle is a strong possibility that complicates efforts to model the geochemical evolution of the Earth.

Reactive ion beam etching of InSb and InAs with ultrasmooth surfaces

The reactive ion beam etching (RIBE) of InSb and InAs using -Ar mixtures was investigated as a function of the gas mixture, ion beam energy, ion beam current density and etching time. It has been shown that with increasing :Ar ratio the morphology of the etched surfaces becomes very smooth. For an ion beam energy of 500 eV the surface roughness (root mean square) of InSb was reduced by more than 2 orders of magnitude because of the utilization of instead of Ar at moderate etching rates. Furthermore, in contrast to pure Ar sputtering, no increasing surface roughness with increasing etching time was observed for the RIBE process.

Volcanic degassing of argon and helium and the history of crustal production on Venus

We develop a new methodology linking 40Ar and 4He degassing to crustal production on Venus in order to examine two different scenarios for the history of magmatism on that planet, both consistent with recent analyses of the cratering record of the Venus surface. The first scenario includes episodic global resurfacing events and modest levels of magmatism between such events, while the second scenario invokes different rates of steady magmatism before and after a given transition time. Our degassing models include distinct mantle, crustal, and atmospheric reservoirs. Diffusive transfer of 40Ar and 4He from the crust to the atmosphere is also taken into account. The 40Ar abundance in the present atmosphere reflects the integrated degassing and magmatism over most of planetary history. In contrast, helium escapes from the planetary atmosphere within a characteristic residence time of 200 Myr to 1.8 Gyr, so the present atmospheric 4He abundance is relevant to the volume of magma produced during the last global resurfacing event and the rate of the magmatism subsequent to that event under the first scenario and to the two steady rates of magmatism and the transition time under the second. Unfortunately, large uncertainties in mineral partition coefficients and in the Ar and He mixing ratios in the lower atmosphere of Venus presently prevent the use of our degassing models to distinguish among crustal formation history models. We therefore explore the influence of these uncertain parameters on the degassing history in order to identify those new laboratory and in situ measurements that will most strongly constrain crustal production history. As an important step in the development of the Ar degassing model, the K budget in the bulk silicate fraction of Venus is re‐examined on the basis of Venera and Vega γ ray measurements of K, U, and Th concentrations in surface materials. For U and Th concentrations in the bulk silicate planet of 18–29 ppb and 64–94 ppb, respectively, the degree of mantle melting that formed the surface materials at the Venera 9 and 10 and Vega 1 and 2 landing sites is calculated to lie between 0.02 and 0.16. The degree of melting calculated for materials at each landing site is combined with measurements of surface K concentration to estimate the K concentration in the bulk silicate portion of the planet at between 100 and 300 ppm. These results suggest that Venus and Earth have similar heat production.

Noble gases, their carrier phases, and argon chronology of upper mantle rocks from Zabargad Island, Red Sea

Three ultramafic bodies on Zabargad Island contain fresh peridotites with mostly unfractionated primitive bulk major and trace element abundances and mostly monomineralic vein rocks (pyroxenites, olivinites, homblendites, etc.). We analyzed a set of coarse grained vein rocks with the 40Ar- 39Ar technique applying high resolution stepheating. Neutron induced argon isotopes derived from Ca, K, and Cl, and the specific degassing behaviour of major and accessory minerals enabled us to separate and identify different trapped and radiogenic argon components and their hosts. Within two clinopyroxenites trapped argon is present in (1) low temperature, low 40 Ar 36 Ar phases (serpentine and/or fluid inclusions), (2) pyroxene-related Cl-rich carriers (pyroxene and/or associated microinclusions) and (3) amphiboles which are intimately and nonseparably intergrown with pyroxene. The amphiboles, which can texturally, chemically, and isotopically be divided into different generations, formed by interaction of spinels and pyroxenes with mantle fluids during different stages of diapiric uplift (Agrinier et al., 1993). Formation of these amphiboles and microinclusions in pyroxenes, along with incorporation of isotopically distinct Ar with 40 Ar 36 Ar ratios up to 8000, can be related to recent mantle metasomatism also evident in Arabian xenoliths (Henjes-Kunst et al., 1990) and must have been induced by a variety of mantle fluids. For a homblendite, in situ radiogenic and excess argon components could be separated: the plateau age of 18.7 ± 1.3 Ma is in perfect agreement with a zircon Pb/Pb age of 18.4 ± 1.0 Ma (Oberli et al., 1987) interpreted as the age of crustal intrusion. Obviously, the formation of the hornblendite occurred during the final stage of uplift, most probably by interaction with seawater, as suggested by strontium, oxygen, and hydrogen isotopic data (Agrinier et al., 1993) and the low 40 Ar 36 Ar ratio (305) of the trapped argon. 4He, 20Ne, 40Ar, and 36Ar were measured in the orthopyroxenite vein rock Z31 by stepwise crushing and subsequent total fusion. Isotopic ratios show a well defined correlation with crushing step that indicates the presence of two different types or generations of inclusions, which were subjected to different degrees of contamination by atmosphere type noble gases. As inclusions were trapped before tje main deformation of the peridotite complex (Kurat et al., 1993), argon with relatively low 40 Ar 36 Ar ratios ( ≤ 1500) was trapped in the mantle, which requires an admixture of argon of atmospheric composition to the source region of the peridotites. Radiogenic isotopes ( 4He, 40Ar) are dominated by the mantle source, however, the 4 He 40 Ar ratio (∼0.16) is much lower than expected from long term decay of radioactive parent nuclides U, Th, and K. Such low ratios, which have previously been observed also in mantle xenoliths, obviously reflect the indigenous peridotitic source and are most probably due to fractionation processes in the mantle.

A reappraisal of the Martian 36Ar/38Ar ratio

The currently used value of 4.1±0.2 for the 36A/38Ar isotopic ratio in the Martian atmosphere is reappraised, and a significantly lower ratio is suggested. Previous analyses of noble gases in impact glass from some Martian meteorites demonstrate that large quantities of Martian atmospheric gases were shock‐emplaced into these samples. However, several observations indicate that this trapped Martian gas is composed of two components, one atmospheric and one probably from the Martian mantle. These observations include large variations in 36Ar/38Ar during stepwise gas release, variations in the Ar/Kr/Xe elemental ratios among Martian meteorites, and variations in the cosmogenic‐corrected, trapped 36Ar/38Ar ratios over 3.5–4.3 among shock glass samples. Uncertainties in applied corrections for cosmogenic Ar cannot explain these variations. By assuming a range of reasonable values for Martian atmospheric and mantle 40Ar/36Ar, the observed 40Ar/36Ar ratios in shock glass are used to correct for the mantle component and to derive a more precise ratio for the atmospheric component. Using this procedure, one obtains an upper limit for Martian atmospheric 36Ar/38Ar of 3.9, and a probable, but poorly defined range for Martian atmospheric 36Ar/38Ar of ∼3.0–3.6. These lower ratios imply that the degree of mass fractionation during Ar loss from Mars' upper atmosphere is considerably larger than that previously calculated.

Cl2/Ar plasma etching of binary, ternary, and quaternary In-based compound semiconductors

A simple Cl2/Ar plasma chemistry can provide smooth, high-rate etching of InP, InAs, InGaAs, A1InAs, and InGaAsP at room temperature under conditions in which there is a balance between formation and sputter desorption of the normally involatile InCl3. When the neutral/ion ratio is either too high or too low, surface roughening is apparent due either to the presence of InCl3, or to preferential loss of the group V element. The etching has been investigated as a function of microwave power (600–1000 W), rf power (0–300 W), process pressure (1.5–10 mTorr), and Cl2:Ar ratio under electron cyclotron resonance conditions. Use of N2 or H2, rather than Ar, as gas additives to the chlorine, did not produce smooth, stoichiometric etched surfaces.

Effect of sputtering atmosphere on superconductivity of La 2−xSr xCu 1−yO 4 thin films

c-axis oriented La 2−xSr xCu 1−yO 4 (x∼0.15) films were grown by dc magnetron sputtering on Y-stabilized ZrO 2, SrTiO 3 and LaAlO 3 substrates. It was found that the zero resistance temperature, T c0, and the lattice parameters of the films are strongly dependent on the sputtering O 2:Ar gas ratios. A strong thickness dependence of T c0 was also found in this kind of film, T c0 of 22 K was obtained on ∼2000 Å thickness film grown on LaAlO 3 substrate. The O 2:Ar ratios primarily modify the copper content, rather than the oxygen content of the films. The variation of the Cu content of the films strongly dominates the seperconductivity of the films.

The Northwest Geysers high-temperature reservoir: evidence for active magmatic degassing and implications for the origin of the Geysers geothermal field

Noble gas isotope abundances in steam from the Coldwater Creek field of the Northwest Geysers, California, show mixing between a nearly pure mid-ocean ridge (MOR) type magmatic gas with high 3He/ 4He and low radiogenic 40∗Ar ( R/ Ra > 8.3 and 40∗Ar/ 4He < 0.07), and a magmatic gas diluted with crustal gas ( R/ Ra < 6.6 and 40∗Ar/ 4He > 0.25). The 3He-enriched component is positively correlated with 4 He/ 40∗ Ar ratios, total helium to non-condensable gas ratios, and the ratios of total helium to atmospheric noble gases, and is accompanied by mantle-like 3He/CO 2 and 4 He/ 36 Ar ratios. The steam samples most enriched in this high 3Hecomponent are produced from a high-temperature reservoir (HTR) and are also the most enriched in total gas and HCl. These results support the hypothesis of active magma degassing beneath the Northwest Geysers, suggest that a significant fraction of the non-condensable gases produced with steam from the HTR is magmatic, and add new constraints to genetic models of the system and its evolution. The intensity of the magmatic signal is inconsistent with deep boiling of connate or metamorphic waters and suggests active magma degassing. A correlation between magmatic helium and non-condensable gases implies that the HTR high-gas component is also magmatic and that the formation of the HTR was possibly related to magmatic intrusion. Magmatic input is unlikely to decline on the time scale of production, but injection of water into the HTR would have multiple benefits: (1) pressure and steam flow would increase; (2) gas concentrations would decrease by dilution with low-gas steam from vaporized liquid; and (3) HCl in steam would be removed once a liquid phase is established. High 3He/ 4He ratios in steam produced from the reservoirs in the southern parts of The Geysers suggest the presence of a similar HTR underlying these portions of the field. Monitoring of 3He content may provide early warning of potential pressure drawdown and entry of corrosive, high-gas HTR steam.