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A "plasma decon chamber" has been developed at Los Alamos National Laboratory (LANL), Albuquerque, NM, to study the decontamination of chemical and biological warfare agents. This technology is targeted at sensitive electronic equipment for which there is currently no acceptable, nondestructive means of decontamination. Chemical reactivity is provided by a downstream flux of reactive radicals such as atomic oxygen and atomic hydrogen, produced in a capacitively coupled plasma. In addition, the decon chamber provides an environment that accelerates the evaporation of chemical agents from contaminated surfaces by vacuum, heat, and forced convection. Once evaporated, agents and agent byproducts are recirculated directly through the plasma, where they undergo further chemical breakdown. Preliminary studies on actual chemical agents were conducted at the U.S. Army Dugway Proving Ground, Dugway, UT. Exposures were conducted at a system pressure of 30 torr, exposure temperature of 70/spl deg/C, plasma-to-sample standoff distance of 10 cm, and 10% addition of oxygen or hydrogen to a helium balance. This exposure condition was based on optimization studies conducted at LANL on agent simulants. The agents studied were VX and soman (GD) nerve agents and sulfur mustard (HD) blister agent, as well as a thickened simulant. All agents were decontaminated off aluminum substrates to below the detection limit of /spl sim/0.1% of the initial contamination level of approximately 1 mg/cm/sup 2/. For VX, this level of decontamination was achieved in 8-16 min of exposure, while only 2 min were required for the more volatile HD and GD. Evaporation and subsequent gas-phase chemical breakdown in the plasma appears to be the dominant decontamination mechanism for all of the agents. However, an observed difference in the decontamination process between oxygen and hydrogen indicates that chemical reactivity in the liquid phase also plays an important role.

Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power. The plasma exiting from between the electrodes was mixed with tetraethoxysilane (TEOS), and directed onto a silicon substrate held at 115-350 °C. Silicon dioxide films were deposited at rates ranging from 20±2 to 300±25 nm min-1. The deposition rate increased with decreasing temperature and increasing TEOS pressure, oxygen pressure and RF power. For the latter two variables, the rate increased as follows: Rd∝P0.3O2(RF)1.4. Films grown at 115 °C were porous and contained adsorbed hydroxyl groups, whereas films grown at 350 °C were smooth, dense and free of impurities. These results suggest that the mechanism in the atmospheric pressure plasma is the same as that in low-pressure plasmas.

Gas breakdown is studied in an atmospheric pressure rf capacitive plasma source developed for materials applications. At a rf frequency of 13.56 MHz, breakdown voltage is largely a function of the product of the pressure and the discharge gap spacing, approximating the Paschen curve. However, breakdown voltage varies substantially with rf frequency due to a change in the electron loss mechanism. A large increase in breakdown voltage is observed when argon, oxygen, or nitrogen is added to helium despite their lower ionization potential. Discussion is given for optimal breakdown conditions at atmospheric pressure.

Tantalum was etched in a downstream, atmospheric-pressure plasma. In this process, etching occurred without significant ion bombardment. An etching rate of 6.0±0.5 μm/min was achieved using 14.8 Torr oxygen, 22.4 Torr carbon tetrafluoride, 720±5 Torr helium, 685 W radio frequency power at 13.56 MHz, and a film temperature of 300 °C. The etching rate increased with the applied power, carbon tetrafluoride pressure, oxygen pressure, and residence time of the gas between the electrodes, indicating that the surface reaction depends on the density of reactive fluorine species generated in the plasma. X-ray photoemission spectroscopy revealed that the etched surface was covered with tantalum fluoride and to a lesser extent, tantalum oxide. Based on these observations, a mechanism for tantalum etching is proposed which involves the reaction between fluorine atoms and the adsorbed tantalum fluoride.

An atmospheric-pressure plasma jet has been used to etch polyimide films at 1.0–8.0±0.2 μm/min at 760 Torr and between 50 and 250 °C. The plasma was produced by flowing helium and oxygen between two concentric electrodes, with the inner one coupled to 13.56 MHz rf power and the outer one grounded. The etch rate increased with the O2 partial pressure, the rf power and the substrate temperature. The apparent activation energy for etching was 0.16 eV. Langmuir-probe measurements revealed that the ion densities were between 1×1010 and 1×1011 cm−3, 5 mm from the end of the powered electrode. Biasing the substrate had no effect on the rate. Ozone, singlet sigma metastable oxygen (b 1Σg+), and singlet delta metastable oxygen (a 1Δg) were detected in the plasma by emission spectroscopy. More ozone was produced in the effluent through the recombination of O atoms with O2. Based on the production rate of O3, the concentration of O atoms 6 mm from the powered electrode was estimated to be ∼7×1014 cm−3 at 6.6 Torr O2...

A plasma jet has been developed for etching materials at atmospheric pressure and between 100 and C. Gas mixtures containing helium, oxygen and carbon tetrafluoride were passed between an outer, grounded electrode and a centre electrode, which was driven by 13.56 MHz radio frequency power at 50 to 500 W. At a flow rate of , a stable, arc-free discharge was produced. This discharge extended out through a nozzle at the end of the electrodes, forming a plasma jet. Materials placed 0.5 cm downstream from the nozzle were etched at the following maximum rates: for Kapton ( and He only), for silicon dioxide, for tantalum and for tungsten. Optical emission spectroscopy was used to identify the electronically excited species inside the plasma and outside in the jet effluent.

Defects caused by particulate contamination are an important concern in the fabrication of thin film products. Often, magnetron sputtering processes are used for this purpose. Particle contamination can cause electrical shorting, pin holes, problems with photolithography, adhesion failure, as well as visual and cosmetic defects. Particle contamination generated during thin film processing can be detected using laser light scattering, a powerful diagnostic technique that provides real-time, in situ imaging of particles >0.3 μm in diameter. Using this technique, the causes, sources and influences on particles in plasma and non-plasma processes may be independently evaluated and corrected. Several studies employing laser light scattering have demonstrated both homogeneous and heterogeneous causes of particle contamination. In this paper, we demonstrate that the mechanisms for particle generation, transport and trapping during magnetron sputter deposition are different from the mechanisms reported in previously studied plasma etch processes. During magnetron sputter deposition, one source of particle contamination is linked to portions of the sputtering target surface exposed to weaker plasma density. In this region, film redeposition is followed by filament or nodule growth and enhanced trapping that increases filament growth. Eventually, the filaments effectively `short-circuit' the sheath, causing high currents to flow through these features. This, in turn, causes heating failure of the filament fracturing and ejecting the filaments into the plasma and onto the substrate. Evidence of this effect has been observed in semiconductor (IC) fabrication and storage disk manufacturing. Discovery of this mechanism in both technologies suggests that this mechanism may be universal to many sputtering processes.

Atmospheric-pressure plasmas are used in a variety of materials processes. Traditional sources include transferred arcs, plasma torches, corona discharges, and dielectric barrier discharges. In arcs and torches, the electron and neutral temperatures exceed 3000/spl deg/C and the densities of charge species range from 10/sup 16/-10/sup 19/ cm/sup -3/. Due to the high gas temperature, these plasmas are used primarily in metallurgy. Corona and dielectric barrier discharges produce nonequilibrium plasmas with gas temperatures between 50-400/spl deg/C and densities of charged species typical of weakly ionized gases. However, since these discharges are nonuniform, their use in materials processing is limited. Recently, an atmospheric-pressure plasma jet has been developed, which exhibits many characteristics of a conventional, low-pressure glow discharge. In the jet, the gas temperature ranges from 25-200/spl deg/C, charged-particle densities are 10/sup 11/-10/sup 12/ cm/sup -3/, and reactive species are present in high concentrations, i.e., 10-100 ppm. Since this source may be scaled to treat large areas, it could be used in applications which have been restricted to vacuum. In this paper, the physics and chemistry of the plasma jet and other atmospheric-pressure sources are reviewed.

Particles or 'dust' in etching or deposition plasmas are an important cause of product yield loss and equipment down-time. Traditional methods of particle control are only partially effective in plasma processing. This is because formation and transport of particles are strongly influenced by plasma electrical and chemical properties. Particle control in plasma processing requires understanding of these effects and their relation to aspects of tool and process design. Laser light scattering has been used to monitor the behaviour of particles for a wide range of plasma tools. This method provides information on location and transport of particles. In some variations, light scattering may also be used for particle size determination. Results have been obtained in sputter, etch and deposition tools of planar diode and magnetron-enhanced designs, Some results have also been obtained in electron cyclotron resonance tools and radiofrequency inductive tools. From this database, differences and common elements are observed for the behaviour of particles. The particle trapping phenomenon is often observed. Particle traps have an important bearing on wafer contamination. Traps cause particles to accumulate into localized regions during plasma operation, only to be suddenly released at the end of the process, thereby contaminating the wafer. Spatially resolved optical emission may be used to map the location and intensity of particle traps. This method also provides a semi-quantitative comparison with two-dimensional modelling studies. It may also be used to optimize grooved electrode design for particle contamination control.

Sources of particles in a closed-coupled electron cyclotron resonance plasma source used for polysilicon etch included flaking of a residual film deposited on chamber surfaces and shedding of material from the electrostatic wafer chuck. A large, episodic increase in the number of particles added to a wafer in a clean system is observed more frequently for a plasma-on than for a gas-only source condition. For film-forming process conditions, particles were added to wafers by a residual film, which was observed to fracture and flake away from chamber surfaces. The presence of a plasma, especially when radiofrequency bias is applied to the wafer, caused more particles to be ejected from the walls and added to wafers than the gas-only condition; however, no significant influence was observed with different microwave powers. A study of the effect of electrode temperatures on particles added showed that thermophoretic and gravitational forces are not significant for this electron cyclotron resonance operating configuration. Particles originating from the electrostatic chuck were observed to be deposited on wafers in much larger numbers in the presence of the plasma as compared with gas-only conditions, implying the existence of a large ion drag force.

An atmospheric pressure plasma source operated by radio frequency power has been developed. This source produces a unique discharge that is volumetric and homogeneous at atmospheric pressure with a gas temperature below 300 °C. It also produces a large quantity of oxygen atoms, ∼5×1015 cm−3, which has important value for materials applications. A theoretical model shows electron densities of 0.2–2×1011 cm−3 and characteristic electron energies of 2–4 eV for helium discharges at a power level of 3–30 W cm−3.

A plasma jet has been developed which deposits silica films at up to at 760 Torr and 115 to C. The jet operates by feeding oxygen and helium gas between two coaxial electrodes that are driven by a 13.56 MHz radio frequency source at 40 to 500 W. Tetraethoxysilane is mixed with the effluent of the plasma jet and directed onto a substrate located 1.7 cm downstream. The properties of the silica films, as determined by infrared spectroscopy and capacitance measurements, are comparable to those of thermally grown silicon dioxide films at C.

Summary form only given, as follows. The atmospheric pressure plasma jet (APPJ) is a unique plasma source operating at atmospheric pressure. The APPJ operates with RF power and produces a stable non-thermal discharge in capacitively-coupled configuration. The discharge is spatially and temporally homogeneous and provides a unique gas phase chemistry that is well suited for various applications including etching, film deposition, surface treatment and decontamination of chemical and biological warfare (CBW) agents. A theoretical model shows electron densities of 0.2-2/spl times/10/sup 11/ cm/sup -3/ for a helium discharge at a power level of 3-30 W cm/sup -3/. The APPJ also produces a large flux, equivalent of up to 10000 monolayer s/sup -1/, of chemically-active, atomic and metastable molecular species which can impinge surfaces several cm downstream of the confined source. In addition, the efforts are in progress to measure the electron density using microwave diagnostics and to benchmark the gas phase chemical model by using LIF and titration.

Summary form only given. Atmospheric-pressure plasma jets can be used for a wide range of materials processing applications, including surface cleaning and modification, selective etching, and thin-film deposition. The plasma source consists of two closely spaced electrodes through which helium and other gases flow (O/sub 2/, CF/sub 4/, etc.). A variety of electrode configurations can be used, and the source is suitable for continuous and large-area processing of materials. Another advantage of the plasma jet is that it achieves etching and deposition rates that are higher than those obtained in low-pressure plasmas. At the meeting, the plasma source will be described in detail, and results for several materials processing applications will be presented.

Discharge phenomena of a nonthermal atmospheric pressure plasma source have been studied. An atmospheric pressure plasma jet (APPJ) operates using rf power and produces a stable homogeneous discharge at atmospheric pressure. After breakdown, the APPJ operation is divided into two regimes, a "normal" operating mode when the discharge is stable and homogeneous, and a "failure" mode when the discharge converts into a filamentary arc. Current and voltage (I–V) characteristics and spatially resolved emission intensity profiles have been measured during the normal operating mode. These measurements show that the APPJ produces an alpha (α) mode rf capacitive discharge. Based upon a dimensional analysis using the observed I–V characteristics, a rough estimate is made for plasma density of 3×1011 cm−3 and an electron temperature of 2 eV. In addition, the gas temperature of 120 °C has been spectroscopically measured inside the discharge. These plasma parameters indicate that the APPJ shows promise for various materials applications as it can produce substantial amounts of reactive species and avoid thermal damages, while having the advantage of atmospheric pressure operation.

Dusty plasmas have recently acquired a lot of attention. The subject was initiated by the semiconductor industry. With the arrival of VLSI and ULSI (very/ultra large scale integration) plasma etching and plasma deposition techniques have become indispensible. With the decreasing feature sizes on the devices the tolerance for dust particles becomes smaller. Now that feature sizes are below 0.25 micron, very small dust particles with a diameter of only a few tenths of a micron can kill the device. Therefore about 5 years ago substantial research efforts were started in order to investigate the trapping and transport of dust particles in processing plasmas.

A technique for collecting spatially resolved optical emission from large rf plasma reactors is described. To demonstrate the sensitivity and versatility of this technique, emission within the quartz ultraviolet, 225–253 nm, was studied with particular emphasis on the “plasma dark space.” Spatial variations of CF2, AlF, and C atom emission were monitored. These results have been used for discussion and evaluation of various plasma excitation and reaction mechanisms involving atomic carbon in fluorocarbon plasmas.

Etude de 800 a 1400 K. On n'a pu deceler que les especes NH et OH. On propose un mecanisme atome/radical pour l'oxydation de NH 3

We have used two‐photon laser‐induced fluorescence to obtain quantitative measurements of the concentration of ground state O atoms in O2+CF4 rf discharges. Absolute calibration was achieved by generating a known concentration of atomic oxygen by UV laser photolysis of O2. Trace amounts of Ar were added to serve as an inert reference gas for concurrent optical emission measurements, in which the plasma‐induced optical emission intensities from O* and Ar* lines were recorded. Emission line shapes were measured using a Fabry–Perot interfermoter to gain information on the mechanisms for formation of excited oxygen atoms in the plasma. Two excitation mechanisms were found to be important: (1) electron impact excitation of ground state atoms, e+O → O*+e, and (2) dissociative excitation of O2, e+O2 → O*+O+e. Evidence for both excitation mechanisms was obtained for O* (8446 A) emission, with atomic excitation being dominant, whereas dissociative excitation appeared to be the dominant mechanism for O* (7774 A) em...

The techniques of optical emission spectroscopy with actinome- try, laser induced fluorescence spectroscopy, laser optogalvanic spectroscopy and absorption spectroscopy are discussed. Examples of the application of these techniques to probing low pressure plasmas of the type used in microe- lectronics materials processing are presented.

A new method, based on the photoelectric effect, is described for real‐time, in situ monitoring of metal or semiconductor surfaces during plasma exposure. As an example of the application of this technique, the effect of both sputter and reactive gas plasma exposure is studied for graphite, silicon, and aluminum surfaces. Results are consistent with the formation of a surface‐passivating layer of fluoride on aluminum and penetration of fluorine into the silicon bulk during exposure to the CF4+Ar etching plasma. An application of this technique for endpoint detection monitoring is described.

We report on in situ detection of diatomic products of plasma sputtering and reactive ion etching using the technique of laser‐induced fluorescence. The diatomic molecules SiN, SiO, and SiF are observed in the gas phase when a silicon surface is subjected to ion bombardment in plasmas containing N2, O2, and CF4, respectively. Information about the production mechanisms is obtained from the measured product concentrations under varying plasma conditions.

A re-investigation of the ultraviolet absorption spectrum of nitrous oxide (N2O) agrees with previous results in the range 210 to 235 nm, but contrary to previous results it indicates a vanishingly small cross section above 260 nm. The absence of the relatively long wave length absorption implies a negligible rate of photolysis of nitrous oxide in the troposphere. These results plus the previously estimated atmospheric mean residence times of N2O indicate that there is a large, unknown tropospheric sink for nitrous oxide.

The catalytic oxidation of NH3 is currently a key industrial synthetic process for HNO3 production. The reaction is known to be very fast and highly efficient [1]. The major products of the reaction on Pt surfaces are H2O and N2 or NO, depending on reaction temperature and the relative concentration of NH3 and O2 according to the following stoichiometries: $$ 4N{H_3}+3{O_2} \to2{N_2}+6{H_2}O $$ $$ 4N{H_3}+5{O_2}\to 4NO + 6{H_2}O.$$

We report quantitative measurements of the concentration of atomic oxygen in RF plasmas determined by two-photon laser induced fluorescence. The results are compared with concurrent measurements of spatially resolved plasma induced optical emission. These measurements establish: (1) the O atom concentration as a function of plasma parameters, (2) a semi-quantitative relationship between O* emission intensity normalized by Ar* in-tensity and O atom concentration, and (3) an understanding of the mechanisms for pro-duction of excited atoms in the plasma.

Laser-induced fluorescence is used to detect a variety of silicon-containing diatomic radicals produced by the reactive ion etching and glow discharge sputtering of silicon and its oxide and nitride. The products include SiN, SiO, and SiF. Examination of the concentration of these molecules as a function of plasma conditions provides information about their production mechanisms.