Metastable Argon Research Articles

Argon metastables in a high density processing plasma

Absolute densities of metastable argon atoms (Paschen 1s5, 1s3) and the intermediate resonant state (1s4) were measured in a high density plasma etching environment. Excited species densities were measured ranging from 108 to 3×109 cm−3, depending on the particular atomic state. A straightforward reaction rate formalism consisting of only two competing electron-atom collision rates accurately predicts such densities. Because of the low densities of these long-lived excited state species, all excited argon species need to be considered only as energy loss channels in modeling high density (1011–1012 cm−3), low pressure (∼1 mTorr) plasma sources. Metastable production rates were also used to identify energy transfer mechanisms under etching conditions of Cl2/Ar mixtures and substrate biasing in the reactor.

Plasma chemistry model of DC magnetron reactive sputtering in Ar[sbnd]O2 gas mixtures

A space averaged model of reactive sputtering which includes plasma chemistry for the first time in DC magnetron discharge has been developed by Ershov and Pekker [A. Ershov. L. Pekker, Thin Solid Films, 289 (1996) 140.]. Argon and oxygen have been chosen in this model as buffer and reactive gases, respectively, and silicon as the target material. The present work is a further development of this model. The present model includes (1) The contribution of secondary electron emission induced by ion bombardment to the total current density and (2) A new plasma chemical reaction of dissociation of molecular oxygen due to its collisions with metastable argon. Thus, the present model has a more advanced plasma chemistry and also allows to take into account the secondary electron emission to investigate reactive sputtering and plasma chemistry. In the model, we show that the consideration of the secondary electron emission can significantly decrease the target erosion rate and shift the hysterisis curves. Numerical calculations also shows that the dissociation of molecular oxygen by metastable argon can significantly change the plasma chemistry equilibrium of the discharge. Generally, deposition of any oxide film can be studied with this model.

Diagnostic of Ar–BCl3 microwave discharges by optical emission spectroscopy

Abstract In this report, Ar–BCl 3 plasmas produced by a 2450 MHz microwave discharge at 700 Pa are investigated by means of optical emission spectroscopy (OES). The emission spectrum of such discharges with high dilution of BCl 3 in argon is very rich in atomic lines (Ar, Cl, B + , Si) and molecular bands (BCl, B 2 , BO). The recently identified (1) 1 Δ u →b 1 Δ g and (2) 3 Π g →A 3 Π u systems of B 2 are observed and two new transitions are attributed to this latter system. Weak BO bands corresponding to the A 2 Π→X 2 Σ + transition are also observed. The excitation channels leading to the formation of these species are analysed by using data obtained by OES. Electron attachment reactions involving BCl 3 are found to be important in the kinetics of the microwave discharge, whereas reactions arising from metastable argon energy transfer must be negligible. Spatial analysis of the microwave discharge by OES is also presented and processes leading to excited B 2 states are discussed. Etching reactions are important through the observation of both Si and BO excited states at the end of the discharge.

High-pressure non-equilibrium microwave plasma source by using carbon materials

A high-pressure (10 torr atmosphere) microwave plasma was generated in a cavity resonator by using carbon materials [reticulated vitreous carbon (RVC)]. In order to investigate the effect of external parameters, the plasma parameters were measured with both probe and optical methods. The results indicated that this plasma was in non-equilibrium state ( T e≫ T g). The metastable argon atoms and thermal electrons are considered as the important elements in generating this plasma and they were measured by the resonant optical absorption method and by the single probe method, respectively. The electron saturation current with RVC was larger than without it, and the RVC temperature was estimated to be about 2400 K from the Richardson–Dushman equation. The concentration of argon metastable atoms was of the order of 10 10 cm −3 and increased slightly with the argon gas flow.

Self-assembled monolayers exposed by metastable argon and metastable helium for neutral atom lithography and atomic beam imaging

We used a beam of noble gas atoms in a metastable excited state to expose a thin (1.5 nm) self-assembled monolayer resist applied over a gold-coated silicon wafer. We determined exposure damage as a function of dose of metastable atoms by processing the samples in a wet-chemical etch to remove the gold from unprotected regions and then measuring the reflectivity with a laser and observing the microstructure with an atomic force microscope. We found that the minimum dose required to damage the resist substantially was 1.7(3)×1015 atoms/cm2 for metastable helium, and 25(7)×1015 atoms/cm2 for metastable argon.

Phenomenology of a dual-mode microwave/RF discharge used for the deposition of silicon oxide thin layers

A remote plasma enhanced chemical vapour deposition (RPECVD) reactor has been developed to deposit silicon oxide films. It consists of a microwave discharge (created by surface waves) along a quartz tube and a capacitively coupled radiofrequency (RF) discharge on a planar electrode (substrate holder) perpendicular to the tube and facing the gas flow. Plasma diagnostics have been performed in Ar, , Ar - and Ar - He - discharges, at two different positions of the reactor. The densities of electrons (a few ), argon metastables (a few ) and oxygen atoms ( - ) have been determined as a function of different plasma parameters, using microwave interferometry and optical emission spectroscopy (self-absorption and actinometry) respectively. In the case of , the gas flow has little effect on the local equilibrium along the discharge tube due to fast quenching on the walls and quenching in the plasma bulk by slow electrons and oxygen molecules. In contrast, the O atom density profile is governed by the gas flow velocity due to a slow recombination probability on the walls. However it clearly appears that the O atom recombination probability is much larger in the microwave discharge region (due to ion bombardment and plasma heating of the walls) than in the afterglow region. We have also shown that the fraction of O atoms with respect to molecules is enhanced by using helium and/or argon dilution due to the production of O atoms by the quenching reactions of or metastables with . Comparing the densities of electrons, argon metastables and oxygen atoms and their respective rate constants for the reaction with silane , we have deduced that the plasma chemical kinetics leading to silicon oxide deposition can be summarized in a simple scheme: electrons dissociate into O atoms and produce which subsequently react with to enhance the O atom density. In the flowing afterglow, is almost entirely decomposed by O atoms, the direct electron impact dissociation being negligible except when applying an RF discharge in the substrate region.

Ionizing Collisional Rate of Metastable Rare-Gas Atoms in an Optical Lattice

Ionizing collisional rate of metastable krypton and argon atoms in an optical lattice k{sub la tt ic e} is compared with that in free space k{sub free} . Reduction of the collisional rate is observed for krypton atoms. However, the magnitude of reduction is no more than a factor of 2 at the laser detuning of 7GHz. The ratio k{sub la tt ic e}/k{sub free} is found to change proportional to the square root of the excitation rate of atoms from the 1s{sub 5} metastable state to the 2p{sub 9} state by the lattice laser. The mechanism that prevents a larger reduction is discussed. {copyright} {ital 1997} {ital The American Physical Society}

Nucleation in superheated liquid argon–krypton solutions

We report nucleation-rate measurements in metastable liquid argon–krypton solutions at pressures of 1.0 and 1.6 MPa over a wide temperature and concentration range. These measurements were performed with the use of a superheated liquid lifetime measurement method. The experimental results are compared with the homogeneous nucleation theory data both using a macroscopic (capillary) approach and taking into account the dependence of critical bubble surface tension on interface curvature. The size effect in nucleation is considered in the framework of the Van-der-Waals, Cahn–Hilliard method. The experimental data indicate that the homogeneous nucleation theory quantitatively describes the kinetics of a first order phase transition in binary solutions of simple liquids if the size effect is taken into account and nucleation rates are J≳106 m−3 sec−1. At J≲106 m−3 sec−1 there is initiated nucleation. A diffusion spinodal of a solution is approximated. The attainable superheating temperature data are presented.

Effect of Ar/H 2 and Kr/H 2 mixtures as discharge gas on the ion intensity in dc glow discharge mass spectrometry

In dc glow discharge mass spectrometry, the addition of small amounts of H2 to pure Ar as discharge gas has greatly increased the ion intensities of elements compared with the conventional method using pure Ar. This phenomenon was also observed for the addition of H2 to pure Kr. The reason for the increase of the ion intensities of elements was studied by using a Kr gas mixture containing 0.2% (v/v) H2. The ion intensities of the elements P, Se and As (whose first ionization potentials are higher than the energy levels of the excited state of Kr) did not increase even if the Kr/H2 gas mixture was used. The results show that the addition of H2 significantly contributed to increasing the number of metastable argon or krypton atoms (Penning ionization).

The radio frequency hollow cathode plasma jet arc for the film deposition

The radio frequency hollow cathode plasma jet (RPJ or RHCPJ) arc discharge is studied for an activated reactive deposition of TiN films. The presence of low content of nitrogen in argon enables reaching the arc regime at lower powers than in pure argon. The transition into the distributed arc after admission of low content of nitrogen results in an extreme enhancement of TiN deposition rate (20–30× higher than for Ti) and at the same time in an effective incorporation of nitrogen into the film. The spontaneously repeated transitions between the hollow cathode discharge and RHCPJ arc at particular parameters are studied. The time development and the character of these transitions confirm the substantial role of metastable argon atoms in the discharge. The comparison of several cathode materials is presented. The reactive deposition of TiN films at low nitrogen pressure without argon is examined.

Using neutral metastable argon atoms and contamination lithography to form nanostructures in silicon, silicon dioxide, and gold

This letter describes the fabrication of ∼80 nm structures in silicon, silicon dioxide, and gold substrates by exposing the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a carbon-based resist. The atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated.

Laser cooling of neutral argon for simulating the storage of antimatter

The storage of antimatter in an electrically neutral state is one of the breakthroughs required to realize antimatter applications. In this work, use of laser cooling to manipulate the motion of neutral atoms by radiative pressure was demonstrated using a commercial laser diode and metastable argon as antimatter simulant. The concept of critical velocity was introduced as a criterion for the laser cooling and its importance was experimentally demonstrated.

Observation of Relative Population Change in the 3P0 and 3P2 States for Ar Glow Discharge Formation

Abstract The formation ratio of the two spin-orbit states, 3P0 / 3P2, of the metastable argon, Ar*, was investigated by the glow discharge of a pulsed Ar supersonic beam. The 3P0 / 3P2 ratio decreased with the increase of the glow discharge potential Vg, by which the electron bombardment initiates the discharge. The observed Vg-dependence clearly showed an inverse behavior against Vg as compared with that in the conventional electron impact by low beam densities.

Modeling of metastable argon atoms in a direct-current glow discharge.

To calculate the behavior of metastable argon atoms in a direct-current glow discharge, a balance equation is constructed, taking into account all known production and loss processes of the metastable atoms. Density profiles and fluxes of the metastable atoms are computed. The relative importance of different production and loss processes determining the metastable density is calculated for the case of a molybdenum cathode in pure argon. Besides electron-impact excitation, fast-ion and atom-impact excitation are found to be the dominant production processes at the high voltages used here, while loss of the metastable atoms is caused predominantly by diffusion and also by electron quenching to the nearby resonant states. The role of metastable atoms in the total discharge is investigated. They are found to play a minor role in the ionization of argon atoms, but their part in the ionization of sputtered molybdenum cathode atoms appears to be rather important. Moreover, they seem to have a significant effect on the secondary electron emission at the cathode. The investigation also includes the influence of pressure, voltage, and current on the metastable densities and fluxes, on the relative importance of the different production and loss processes, and on the role of metastable atoms in the entire discharge.

Absolute density of the argon first excited states in plasmas used for carbon deposition as determined by absorption spectroscopy

Abstract In order to study the possible excitation transfer from argon metastables to the admixed species in an expanding cascaded arc plasma the densities of the Ar(3 p 5 4 s ) states in a deposition plasma were studied with absorption spectroscopy. For a purely argon plasma the Ar(3 p 5 4 s ) density lies in the range 10 16 –10 18 m −3 at a chamber pressure of 40 Pa. The effect on the densities of the addition of moderate amounts of methane and oxygen is small. The addition of hydrogen to the argon plasma leads to a rapid disappearance of the argon 4 s states. Possible explanations are a lowering of the argon ion density by dissociative recombination and the direct excitation energy transfer with the H ∗ ( n = 2, 3) levels.

Microlithography uses metastable argon atoms

A new microlithography technique that uses atoms instead of light to create patterns on an etchable substrate has the potential to create far tinier and more unusual structures than standard photolithography. The new method—described in last week's Science [ 269 , 1255 (1995)] by scientists at Harvard University and the National Institute of Standards & Technology (NIST)—exploits the wavelike nature of atoms to do tasks more commonly thought of as suited for light. Conventional lithography is performed by projecting a pattern onto a lightsensitive surface to selectively remove the surface layer, exposing a substrate beneath that can then be chemically etched. The Harvard/NIST team—led by Harvard chemistry professor George M. Whitesides and Harvard physics professor Mara Prentiss—finds that metastable neutral argon atoms can be used to damage alkanethiolate self-assembled monolayers that cover an etchable base. The new method has several advantages, the researchers say. Diffraction limits conventional phot...

Microlithography by using neutral metastable atoms and self-assembled monolayers.

Lithography can be performed with beams of neutral atoms in metastable excited states to pattern self-assembled monolayers (SAMs) of alkanethiolates on gold. An estimated exposure of a SAM of dodecanethiolate (DDT) to 15 to 20 metastable argon atoms per DDT molecule damaged the SAM sufficiently to allow penetration of an aqueous solution of ferricyanide to the surface of the gold. This solution etched the gold and transformed the patterns in the SAMs into structures of gold; these structures had edge resolution of less than 100 nanometers. Regions of SAMs as large as 2 square centimeters were patterned by exposure to a beam of metastable argon atoms. These observations suggest that this system may be useful in new forms of micro- and nanolithography.

半導体レーザーによる励起アルゴン流の速度計測

The velocity of a metastable argon flow was measured by means of laser induced fluorescence (LIF). A commercial laser diode was employed as the diagnostic instrument. The transition between 1 s5 and 2 p6 was available for LIF and the resultant fluorescence in a vacuum ultraviolet range was detected by an electron multiplier. The velocity of the argon flow estimated at 750m/s and its number density ranged around 103 particles per cm3.

Quenching collisions of low-energy metastable multiply charged argon ions.

Quenching collisions of low-energy metastable multiply charged argon ions.

Reflection of atoms from a dielectric wave guide

We report on the reflection of metastable argon atoms from an evanescent wave enhanced by means of a dielectric wave guide by two orders of magnitude in intensity. This allows to reflect atoms with an incidence velocity of up to 3 m/s. We compare the experimental results to a theoretical model by means of a Monte-Carlo simulation.