bluuebunny/crossref_metadata_2025 huggingface dataset:
Pumping characteristics of a cryopump with Ar sorbent in He and in a D2/He mixture
Authors: Menon M. M. , Laughon G. J. , Maingi R. , Wade M. R. , Hillis D. L. , Mahdavi M. A.
Published: July 2002

The He generated as a result of D/T burn in a fusion reactor must be exhausted from the plasma to avoid fuel dilution effects. In view of this, transport and exhaust studies of He in fusion plasmas are getting increasing attention in recent years. In fusion plasmas, the exhaust gas will be a combination of D2 and He, with He forming only a small fraction (about 10%). The cryosorption pumping characteristics of pure He and a mixture of D2 and He (90% D2) have been investigated using a cryosorption pump with condensed layers of Ar as sorbent. A cryocondensation pump cooled by liquid He at 4.3 K, and located in the outboard divertor region of the DIII-D tokamak, was used for the experiment. The investigation was conducted in a pressure regime that is relevant for particle exhaust from fusion plasmas. The experiment revealed that (1) the cryosorption pumping speed of pure He drops precipitously if the Ar/He ratio falls below about 20; (2) the pumping speed for He in a D2/He mixture decreases in an exponential manner with the amount of D2 pumped; (3) increasing the thickness of Ar in the range of 1–12 μm had little effect on the pumping speed for He in a D2/He mixture; and (4) for a pumping surface coated with a thick (≳2 μm) layer of Ar, surrounded by a radiation shield having a transparency factor of about 6, a He pumping speed in the range of 15–25 m3 s−1 m−2 in the mTorr pressure range for a pulse duration of about 5 s can be obtained after pumping about 80 Torr ℓ of D2.
High rate and highly selective SiO2 etching employing inductively coupled plasma and discussion on reaction kinetics
Authors: Horiike Yasuhiro , Kubota Kazuhiro , Shindo Haruo , Fukasawa Takayuki
Published: July 2002

High rate and highly selective SiO2/Si etching employing a C4F8+H2 mixture was achieved in the diffusive region of an inductively coupled plasma where electrons in its diffusive region were not so energetic. It was considered that hydrogen fluoride formed by hydrogen introduced to scavenge fluorine (F) radicals was not dissociated in the region and was exhausted outside. The carbon-rich film was deposited selectively on the Si surface, thereby providing high selectivity. The thick film, in particular, deposited selectively onto the bottom of holes below 1 μm and exposure of C4F8+30% H2 for as-etched holes at floating potential showed that polymer films conformed to the inner surfaces of holes. Hence, this selective deposition was ascribed to the accumulation of the resputtered polymer on the bottom films. Appearance mass spectroscopy measurements of fluorocarbon radicals for some discharge conditions showed that the CF1 radical played a major role in the polymer film deposition, while the CF2 radical might not contribute to the polymer deposition and a sticking probability of the CF1 radical was reduced considerably in the presence of hydrogen. A simulated etching experiment using a capillary plate mask made it clear that the carbon-rich polymer film was deposited on the Si bottom surface in the presence of hydrogen at a high CF1/CF2 radical density ratio. Accordingly, CF1 radicals whose surface loss is suppressed in the presence of hydrogen were likely to arrive at a deep bottom surface, forming a carbon-rich polymer by scavenging fluorine from CF1 radicals with hydrogen.
High power density pulsed plasma deposition of titanium carbonitride
Authors: Yan P. X. , Yang S. Z. , Li B. , Chen X. S.
Published: July 2002

Titanium carbonitride [Ti(CN)] films were deposited on the surface of No. 45 steel for modification using the high power density pulsed plasma technique. The pulsed plasma is generated from a coaxial plasma gun and has a high electron temperature of 105–106 K and a high electron density of 1014–1016 cm−3; high translation titanium carbonitride [Ti(CN)] films were deposited at 30–50 km/s and were only 60 μs wide. The substrates were maintained at room temperature during the film deposition, but a stronger adhesion of film to substrate existed. A wide mixing interface between the Ti(CN) films and the substrate formed and resulted in a high adherency of the films to the substrate. The surface microhardness of No. 45 steel increased remarkably due to the formation of titanium carbonitride films.
Intrinsic stress and its relaxation in diamond film deposited by hot filament chemical vapor deposition
Authors: Choi S. K. , Jung D. Y. , Choi H. M.
Published: July 2002

Intrinsic stress in diamond films fabricated by hot filament chemical vapor deposition was investigated as a function of deposition temperature, CH4 concentration, and positive bias voltage. The intrinsic stress in the diamond film was tensile between 810 and 980 °C. The minimum tensile stress existed at 880 °C. The relationship between tensile intrinsic stress and deposition temperature was explained by the nondiamond phase and crystallite size. The tensile intrinsic stress decreased almost linearly with CH4 concentration in the range of 0.4%–1.2%. Applying +50 V to the Si substrate, the tensile intrinsic stress was reduced from 2.4 to 0.7 GPa without any change in the quality of the diamond film. This relaxation was attributed to the β-SiC buffer layer formed by electron bombardment onto the Si substrate.
Role of nitrogen in the downstream etching of silicon nitride
Authors: Blain M. G. , Meisenheimer T. L. , Stevens J. E.
Published: July 2002

Chemical downstream etching of silicon nitride (Si3N4) requires the addition of nitrogen to the discharge for obtaining efficient etch rates. A 10% addition of N2 to a CF4/O2 discharge (CF4/O2 = 1.2, 0.525 Torr) causes a factor of 6 increase in the Si3N4 etch rate and a 8% decrease in the silicon dioxide etch rate. The result is selectivities approaching 9:1. Importantly, the conversion of CF4 to F and F-containing reactive species by the discharge decreases or remains constant as nitrogen is added to the discharge mix, indicating that the etching reaction is not limited by delivery of these species to the substrate. By measuring the amount of NO and NO2 in the etch chamber, it is found that the NO concentration increases by a factor of 6 as N2 is added, while the amount of NO2 remains small and constant. The NO signal is significantly reduced during nitride etching compared to the signal observed during a discharge with an empty etch chamber, implying that the increase in Si3N4 etch rate is related to the formation of NO in the discharge. This view is consistent with the observation that an NF3 plasma in a quartz discharge tube results in a nitride etch rate which is a factor of 2 higher than for the same discharge in a sapphire tube. The conclusion is that the oxygen liberated by erosion of the quartz tube allows the formation of NO. That NO is a key Si3N4 etch reactant was confirmed by performing a series of experiments in which N2, NO, NO2, and N2O were injected into the discharge and then downstream in the reaction chamber during a CF4/O2 discharge. Nitride etch rates increased significantly upon injection of NO into both discharge and etch chamber as compared to injection of the other NxOy species.
Preparation and characterization of a well-ordered surface on a Si(001) substrate with a buried metal layer for application of infrared reflection spectroscopy
Authors: Kobayashi Yoshihiro , Sumitomo Koji , Prabhakaran Kuniyil , Ogino Toshio
Published: July 2002

The preparation and characterization of an atomically flat and well-ordered surface on the Si(001) substrate with a buried metal layer (BML) are reported. The BML substrate was formed by implantation of Co+ ion and subsequent annealing. After molecular beam epitaxy growth of the Si overlayer on the cleaned BML sample in ultrahigh vacuum, clear 2×1 patterned and ordered steps with regular terrace width were observed by reflection high energy electron diffraction and atomic force microscopy. No contamination, including Co, was observed in the spectra of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectra showed a distinct surface peak that originated from surface dangling bonds and is characteristic of a clean and ordered surface. The surface atomic structure, including stress and damage caused by ion implantation, was characterized by medium energy ion scattering (MEIS). Very low χmin (1.7% with 300 keV H+) and a dip pattern in blocking profile in the MEIS spectra indicate that surface crystal quality is comparable to that of a homoepitaxially grown Si layer on normal Si substrate without BML. These results show that the BML substrate obtained by the procedure is quite useful for the structural investigation of surface species on Si by infrared (IR) reflection spectroscopy. Typical examples of IR spectra qualifying the BML substrate for surface studies are also presented.
Experiments and modeling of a helicon source
Authors: Molvik A. W. , Rognlien T. D. , Byers J. A. , Cohen R. H. , Ellingboe A. R. , Hooper E. B. , McLean H. S. , Stallard B. W. , Vitello P. A.
Published: July 2002

We report on experimental results from the Lawrence Livermore National Laboratory Helicon Source plasma source and numerical models used to understand the observations. These include measurements of plasma density with Langmuir probes, and heating measurements with an electron energy analyzer to test transit-time heating. The models describe helicon wave excitation, and electron heating. The wave fields are calculated using the ANTENA code including collisional and electron Landau heating. Numerical and analytic models are used to describe transit-time heating of electrons and quantify the effect of collisions.
Particle emission debris from a KrF laser–plasma x-ray source
Authors: Bobkowski R. , Fedosejevs R.
Published: July 2002

The production of plasma debris ejected from various solid targets heated and ionized by intense KrF laser pulses was studied. The plasma is produced by focusing a train of 50 ps KrF laser pulses to an 8-μm-diam spot on the surface of solid tape targets. The plasma conditions are those of interest for the generation of a point source of the keV and sub-keV x rays for microlithography (Cu and Fe targets) and x-ray microscopy (plastic targets). Experimental measurements of the amounts of debris produced, the statistical distribution of the debris size, and angular distribution in vacuum are presented. The results of similar measurements in a background gas of helium are also presented together with measurements of the stopping power of the gas. A large flux of micron and submicron size particles is generated in vacuum even when employing thin tape targets. The introduction of a background gas reduces the damaging influence of such particles dramatically but only if enough path length exists to stop the particles. Theoretical calculations have been carried out of the stopping power of the background gas based on Stokes law and the Newtonian theory of deceleration of particles in gas.
Simple procedure for the control of the transport of reactants by carrier gas flow
Authors: Lakshmikumar S. T.
Published: July 2002

A simple inexpensive procedure for the control of the reactant transported by the carrier gas from solid sources is proposed. A provision for controlled redeposition of the reactant and modification of the carrier gas flow permit the variation of the mixing between the carrier gas and the reactant species. An approximate estimation of the pressure regime over which the reactant concentration varies significantly is made. The procedure has been experimentally verified in the case of Se vapor selenization of metal films. This procedure enables the use of total reactor pressure as a simple control parameter for a significant variation of the reactant availability which is very useful in the exploration of alternate reaction pathways.
Characterization of a low-frequency inductively coupled plasma source
Authors: Tuszewski M. , Tobin J. A.
Published: July 2002

A hemispherical inductively coupled plasma source is characterized with Langmuir probes, microwave interferometry, voltage, and current monitors, optical emission, and mass spectrometry. The plasma source is operated with up to 2 kW of 0.46 MHz rf power and with a 5 mTorr mixture of argon, oxygen, and hydrogen gases. The rf power is efficiently coupled to the plasma. The ion and neutral compositions show substantial dissociation and water vapor formation. Maps of ion density, electron temperature, and plasma potential are obtained that are consistent with diffusive particle transport and edge power deposition. The latter contributes to an excellent plasma radial uniformity near the bottom electrode.
β-hydride elimination processes on silicon
Authors: Klug Debra-Ann , Greenlief C. Michael
Published: July 2002

The adsorption and decomposition of ethylbromide on the Si(100) and Si(111) surfaces is investigated. Ethylbromide adsorbs molecularly on Si at surface temperatures below 110 K. Warming the ethylbromide-covered surface above 200 K results in the cleavage of the carbon–bromine bond with the formation of surface ethyl groups and coadsorbed bromine atoms. Further heating of the surface leads to the decomposition of surface ethyl groups which desorb as ethylene leaving hydrogen at the Si surface. The hydrogen atoms recombine at higher surface temperatures (near 800 K) and desorb as molecular hydrogen. Isotopic labeling of the hydrogen within the ethyl group provides greater insight into the mechanism for ethylene formation. A branching reaction is observed between β- and α-hydride elimination within the ethyl group to form ethylene. The ratio of the amount of ethylene produced by β-hydride to α-hydride elimination can be varied by the position of the deuterium label within the ethyl group. The reaction rate for ethylene production is measured and how this rate is influenced by the isotopic substitution is discussed.
Surface damage in the submonolayer growth of carbon on Si(111)7×7 by means of the laser ablation deposition technique
Authors: Dı́az J. , Martin-Gago J. A. , Ferrer S. , Comin F.
Published: July 2002

Carbon was deposited on the Si(111)7×7 reconstructed surface at room temperature under ultrahigh vacuum conditions, by the pulsed laser deposition technique. The laser power density was 1010 W/cm2. Scanning tunneling microscope images at submonolayer coverages revealed damage on the surface in the form of vacancies, clusters of vacancies, and displaced atoms, avoiding the formation of a crystalline interface. The magnitude of the damage and the low proportion of fast ionized species measured in the plume indicated that the kinetic energy of the nonionized particles was much larger than that produced in a thermal evaporation process. The combination of ion scattering spectroscopy and Auger electron spectroscopy suggested that carbon deposited by this technique grew implanted in the subsurface. Further coverages above 1 ML showed a moderate increase in the roughness of the surface from 0.8 Å root mean square (rms) of the clean Si(111) reconstructed surface to 1.3 Å rms above 1 deposited ML of carbon.
Molecular dynamics simulations of fluorosilyl species impacting fluorinated silicon surfaces with energies from 0.1 to 100 eV
Authors: Helmer B. A. , Graves D. B.
Published: July 2002

A better understanding of the surface interactions of energetic atomic and molecular species is needed under conditions relevant to plasma-assisted etching and deposition. In this article we describe the results of molecular dynamics (MDs) simulations of atomic Si and molecular SiFx (x=1–3) species impacting fluorinated silicon surfaces. These impacting species might be sputtered species incident on feature surfaces with energies typically on the order of a few eV, or etch products that are ionized in the plasma and accelerated back towards the substrate surface to attain energies on the order of tens to hundreds of eV. To model both of these cases, the incident energy was varied from 0.1 to 100 eV. We performed the MD simulations to investigate the types of possible events that occur during the picosecond(s) following the impact of these reactive atomic and molecular species. Stillinger–Weber potentials were used to model the interatomic interactions [Phys. Rev. B 31, 5262 (1985); J. Chem. Phys. 88, 5123 (1988); Phys. Rev. Lett. 62, 2144 (1989); J. Chem. Phys. 92, 6239 (1990)]. We observed a variety of events in the simulated trajectories: sticking or reflection of the impacting species, reactions with surface species, sputtering of surface material, and dissociation of the impacting molecular species. The effect of surface coverage and incident angle was studied by simulating impacts onto three silicon surfaces with different amounts [monolayers (MLs)] of fluorine (0 ML F, 1 ML F, 2 ML F), and by varying the incident angle of Si atoms from 0° to 75° from the surface normal. These effects are illustrated for select cases.
Diffusion mechanisms of n-butane on Pt(111) and Cu(001): Unique molecular features
Authors: Raut Janhavi S. , Fichthorn Kristen A.
Published: July 2002

We have used transition-state theory to estimate diffusion-energy barriers and to determine the characteristic mechanisms by which n-butane diffuses on model Pt(111) and Cu(001) surfaces. Our studies reveal some of the unique features associated with molecular mobility, including one-jump mechanisms for molecular hopping between non-nearest-neighbor binding sites; conformational correlation in molecular hopping; short-ranged, directional anisotropy in diffusion induced by the molecular degrees of freedom; and the role of multiple-binding sites in various hopping mechanisms. We discuss some experimental ramifications of these unique features.
Formation of NH3 and N2 from atomic nitrogen and hydrogen on rhodium (111)
Authors: van Hardeveld R. M. , van Santen R. A. , Niemantsverdriet J. W.
Published: July 2002

Reactions of adsorbed N atoms on Rh(111) to N2 and NH3 were studied with temperature programmed desorption, temperature programmed reaction spectroscopy, and static secondary ion mass spectrometry. For N-atom coverages below ≈0.15 monolayers, desorption of N2 follows simple second-order kinetics, but at higher coverages the desorption traces broaden to higher temperatures. Hydrogenation to NH3 can be described by a stepwise addition of H atoms to Nads in which the reaction from NH2,ads+Hads to NH3,ads determines the rate. The activation energy for the rate determining step is 76 kJ/mol. The desorption of NH3 from Rh(111) was studied separately. The kinetic parameters for desorption at low NH3 coverage are 81 kJ/mol and 1013 s−1, but the rate of desorption increases rapidly with increasing NH3 coverage. It is argued that the remarkable coverage dependence of the desorption rate is unlikely to be caused by lateral repulsive interactions but may be due to a coverage dependence of the pre-exponential factor.
Some characteristics of wide gap a-SiC:H films deposited by electron cyclotron resonance chemical vapor deposition using acetylene
Authors: Yoon S. F. , Ahn J.
Published: July 2002

The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene, and hydrogen gas using the electron cyclotron resonance chemical vapor deposition process is reported. The variation of the deposition and film characteristics such as the deposition rate, optical band gap, photoluminescence, and the infrared (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of ∼250 Å/min at a moderate hydrogen dilution ratio of ∼20 [hydrogen flow (sccm)/acetylene +silane flow (sccm)], and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical band gap on the hydrogen dilution within the dilution range investigated (10 to 60), and the optical band gap calculated from the E04 method varied marginally from ∼2.85 to ∼3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of ∼2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of ∼30. The PL intensity showed a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more Si–C bonding.
Frequency dependence of helicon wave plasmas near lower hybrid resonance frequency
Authors: Yun Seok-Min , Kim Jung-Hyung , Chang Hong-Young
Published: July 2002

The frequency dependence of helicon wave plasmas has been studied at 1–25 MHz of rf power, and at magnetic fields of 200–1150 G using various gases. Maxima in the electron density occur for particular frequencies at each magnetic field. These optimum frequencies are propor-tional to magnetic field strength and inversely proportional to the discharge gas mass. The exist-ence of optimum frequencies in each magnetic field and gas mass indicates the possibility of lower hybridresonance heating effect. The experimental optimum frequencies are slightly lower than the theoretical lower hybrid resonance frequencies. The difference between the two frequencies can be explained by the Doppler shift effect.
Rapid thermal processing of III-nitrides
Authors: Hong J. , Lee J. W. , Vartuli C. B. , Abernathy C. R. , MacKenzie J. D. , Donovan S. M. , Pearton S. J. , Zolper J. C.
Published: July 2002

High-temperature annealing is necessary in a number of applications for III-nitrides, including activation of Si+ or Mg+ implants for doping, maximization of implant-isolated regions, and Ohmic contact sintering. We have compared two methods for protection against surface dissociation of GaN, AlN, InN, InxGa1−xN, and InxAl1−xN during rapid thermal processing in N2 ambients. In the first method, AlN or InN powder is placed in the reservoirs of a SiC-coated graphite susceptor and provides a N2 overpressure for the nitride samples within the susceptor. In the second method, the nitrides are placed face down on other III–V substrates during annealing. In both techniques N loss from the nitride surface is found to occur at ⩾1050 °C for GaN and ⩾1100 °C for AlN and ⩾InN, as measured by Auger electron spectroscopy. Real surface roughening is generally significant only for the In-containing materials, with GaN and AlN retaining smooth morphologies even up to 1150 °C unless H2 is present in the annealing ambient. When InN powder is used in the susceptor, there is In droplet condensation on the surfaces of all samples above ∼750 °C leading to higher root-mean-square surface roughness measured by atomic force microscopy. The N2-deficient surfaces of the binary nitrides become strongly n type, while those of ternaries become less conducting. At temperature of 850–900°C, the In droplets on thermally degraded ternaries also begin to evaporate, leading to an apparent improvement in morphology. The presence of H2 or O2 in the annealing ambient lowers the dissociation temperature of each of the nitrides by 100–200 °C, due to an enhancement in N2 removal.
X-ray photoelectron spectroscopy characterization of semiconductor thin films using simultaneous Mg/Zr excitation
Authors: Allgeyer Daniel F.
Published: July 2002

This article presents a method for determining the interfacial chemical composition of semiconductor thin films. Some of the materials and interfaces characterized by this technique are tungsten silicide, titanium nitride, silicon nitride, titanium silicide, and aluminum. These thin film materials are typically supported on conductive (silicon, polysilicon) and nonconductive (boron-doped phosphosilicate glass) substrates. The determination of their interfacial chemical compositions is enhanced by using the zirconium anode (2042.4 eV). The simultaneous use of magnesium and zirconium anodes allows the analysis of the photoelectrons as well as the corresponding higher energy Auger electrons for such materials as silicon and aluminum. The kinetic energies of the Al KLL and Si KLL are beyond the Fermi level (zero binding energy) of either the magnesium (1253.6 eV) or aluminum (1486.6 eV) anodes. The photoelectron used in conjunction with thin film Auger electrons provides the energy necessary for determining Auger parameters, which are independent of localized sample charging and provide their chemical identification. Charging is common to many of these materials and is especially prevalent when analyzed using an increasingly common monochromatized aluminum source for excitation. Thus, the simultaneous use of the magnesium (1253.6 eV) and zirconium (2042.4 eV) anodes is charge independent and provides interfacial chemical identification.
Direct dissociative chemisorption of methane, ethane, propane, and cyclopropane on Ir(110)
Authors: Kelly D. , Weinberg W. H.
Published: July 2002

We have employed molecular beam techniques to investigate the initial probability of direct dissociative chemisorption of perhydrido- and perdeuteromethane, ethane, propane, and cyclopropane on Ir(110) as a function of beam translational energy from 1.5 to 59 kcal/mol. For each of the saturated perhydridoisotopomers, a measurable (>0.02) initial probability of direct dissociative chemisorption is observed above a beam energy of approximately 7 kcal/mol. In the case of the saturated perdeuteroisotopomers, this “threshold” energy is approximately 10 kcal/mol. For cyclopropane, the relevant energy is approximately 5 kcal/mol for both c-C3H6 and c-C3D6. Above these energies, the initial probability of direct chemisorption of each of these hydrocarbons increases approximately linearly with beam translational energy and is independent of surface temperature, indicative of direct dissociative chemisorption. However, the energy required to achieve a measurable (>0.02 in this experiment) initial probability of direct chemisorption is independent of carbon chain length for the saturated perhydrido- and perdeuterohydrocarbons, and is slightly lower for cyclopropane. This observation is explained by considering bond energetics, since in each case the initial bond cleaved (C–H for methane, ethane, and propane, and C–C for cyclopropane) upon chemisorption is of comparable strength.
Structure of methyl nitrite on Ag(111)
Authors: Fieberg Jeffrey E. , White J. M.
Published: July 2002

The structure of saturated monolayer methyl nitrite, CH3ONO, on Ag(111), as determined by reflection-absorption infrared spectroscopy (RAIRS), is presented. Methyl nitrite adsorbs molecularly, monolayer desorption peaks at 122 K, and there is no evidence for thermal decomposition. RAIRS indicates that adsorbed methyl nitrite, at 104 K, is dominated by the cis isomer (>90%) and bonds weakly to Ag through the lone pair electrons of the internal oxygen. From analysis of relative band intensities, we conclude that the Cs plane of adsorbed CH3ONO lies near the surface normal and the N–O bond containing the internal O is tilted ∼45° from the surface normal. This orientation is consistent with the facile ejection of NO observed in previous photochemistry experiments.
Surface morphology of ex situ sulfur-passivated (1×1) and (2×1) InP(100) surfaces
Authors: Qin X. R. , Lu Z. H. , Shapter J. G. , Coatsworth L. L. , Griffiths K. , Norton P. R.
Published: July 2002

Ex situ aqueous (NH4)2S treated sulfur-passivated InP substrates have been studied using ultrahigh vacuum scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED). The morphology of the passivated surface was imaged after a mild sample annealing. The STM images of a surface exhibiting a good 1×1 LEED pattern show that the top layer of the sulfur-passivated surface is poorly ordered. A surface bilayer atomic step has been observed to be common on sulfur-passivated surfaces. The magnitude of the surface roughness for the passivated surfaces lies between 10 Å and 25 Å; this is much smaller than the roughness of InP(100) substrates prepared using previously published methods. After annealing the sample at ∼420 °C, a (2×1) LEED pattern with split half-integer spots has been observed. The associated STM images show that these split half-integer diffraction beams correspond to regularly spaced domains with a width of ∼20–30 Å in the [011̄] direction. The surface roughness increases with annealing temperature; the surface corresponding to the best 2×1 LEED symmetry (annealing at ∼420 °C) has a roughness double that of the 1×1 phase.
C
2
column densities in H2/Ar/CH4 microwave plasmas
Authors: Goyette A. N. , Matsuda Y. , Anderson L. W. , Lawler J. E.
Published: July 2002

We report the observation of the d 3Πg→a 3Πu Swan bands of the C2 molecule both in absorption and emission in a H2/Ar/CH4 microwave discharge plasma. The input mole fraction of methane is varied from 1% to 33%. From the observed absorptions, we calculate the column density of gas phase C2. The calculated concentration of C2 is higher in discharges containing large fractions of argon than in discharges containing large fractions of hydrogen. These observations are useful in understanding the contribution of the C2 molecule to the gas phase chemistry of the microwave plasma-assisted chemical vapor deposition of diamond.
Plasma research activities in the association of super-advanced electronics technologies
Authors: Inoue Masami , Ishitani Akihiko , Samukawa Seiji , Sekine Makoto
Published: July 2002

Association of super-advanced electronics technologies (ASET) is a Japanese electronics research and development consortium that was founded on 29 February 1996. The target of the plasma research group in ASET is to make breakthroughs for future dry etching technology by investigating the mechanisms of dry etching scientifically. The plasma research group is investigating plasma diagnostics, plasma generation and its transportation, plasma surface reaction and vapor phase reaction, plasma modeling/simulation directed toward plasma control, and the mechanism of silicon oxide etching in high aspect ratio, narrow contact holes, and will develop a new chemistry, a new plasma source, and a new monitoring method.
Accurate determination of the optical constants of sputter-deposited Ag and SnO2 for low emissivity coatings
Authors: Martı́n-Palma R. J. , Martı́nez-Duart J. M.
Published: July 2002

The determination of the values of the optical constants (n, refractive index and k, extinction coefficient) in the visible range (400–700 nm approximately) of both silver (Ag) and tin oxide (SnO2) films is a necessary condition to predict the behavior of a SnO2/Ag/SnO2 multilayer low emissivity coating in relation to visual comfort. For this purpose, thin films of Ag and SnO2 with a thickness similar to that in multilayer coatings (90 and 380 Å, respectively) were used in order to avoid the thickness dependence of the optical constants. A simulation computational program based on the matrix method was employed to determine the values of the optical constants of these films in the visible range. It has been demonstrated that for the design of optical coatings with optimal properties it is essential a great accuracy in the determination of the optical constants, since a minimum variation of these values leads to a deterioration of the behavior of the whole coating.
Plasma source ion carburizing of steel for improved wear resistance
Authors: Lei M. K. , Zhang Z. L.
Published: July 2002

Plasma source ion carburizing is a low-temperature, low-pressure carburizing approach for improved wear resistance of steel with specific advantages over plasma carburizing and plasma source carbon ion implantation. A carburizing apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Carbon (as methane and hydrogen) ions are accelerated from the ECR plasma by a low-pulsed negative bias (typically −2 kV), which is applied directly to the sample, implanted, and are finally diffused into the steel at elevated temperatures that are regulated up to 550 °C by an auxiliary heater. Plasma source ion carburizing into pure iron and 35CrMo low alloy steel at a process temperature of 350 °C has been investigated. The carburized samples were characterized using Auger electron spectroscopy, electron probe microanalysis, microhardness measurement, and glancing incidence x-ray diffraction. Significant increases in microhardness have been observed on the carburized pure iron and 35CrMo steel, because of 10 μm thick carburized layers composing a Fe3C phase on the outer surface and a hardened diffusion zone in the matrix that were formed after the carburizing at 350 °C for 8 h. The wear tests were performed on a crank/connecting rod reciprocating tribometer in a flat-on-flat configuration. The test results indicate that the carburized 35CrMo steel improved the abrasive wear resistance and decreased the coefficient of friction in comparison with the uncarburized steel.
The retardation of aluminum-amorphous silicon interaction by phosphine plasma treatment
Authors: Wei Jeng-Hua , Lee Si-Chen
Published: July 2002

Aluminum interacts with amorphous silicon (a-Si:H) at an annealing temperature beyond 170 °C. However, by increasing the phosphorus concentration in the a-Si:H alloys, the Si recrystallization rate at the Al/a-Si:H interface decreases appreciably even when annealed at 250 °C. As the phosphorus concentration is increased to a very high level, the recrystallization process will eventually be stopped. Applying this concept, the surface of the phosphorus doped a-Si:H is pretreated by PH3 plasma before the deposition of the aluminum, the annealing results show that this pretreatment step can perfectly protect the upper surface of a-Si:H even when annealed at 300 °C. This technology can be applied to the a-Si:H thin film transistor with the Al metal contact and the a-SiNx:H passivation layer and can be deposited at the higher temperature to achieve better quality.
Laser ablation and gas-phase reactions of small gold cluster ions, Aun+ (1⩽n⩽7)
Authors: Gibson John K.
Published: July 2002

The abundance distributions of gold cations, Aun+ for 1⩽n⩽7, generated by pulsed laser ablation of gold metal were determined by time-of-flight mass spectrometry. The odd-n ions, Au3+, Au6+, and Au7+ were particularly abundant, consistent with previous results understood by rudimentary molecular orbital bonding models. A unique aspect of our experiment was the ability to enhance concentrations of the larger Aun+ by sampling slower ions in the tail of the ablation plume; this effect indicates ion formation under quasiequilibrium (high temperature) conditions. The primary goal of this study was to examine gas-phase reactions of Aun+ for n=1–7 by injecting a hydrocarbon or halocarbon into the ion trajectory and determining compositions/abundances of the resulting complex ions, Aun+-L, formed by abstraction of a ligand(s) L from the organic molecule(s). Among the more significant products were the carbides AunCc+, for n⩽7 and c⩽4. The Aun+-L products and distinctive n-dependent variations in product compositions and abundances are interpreted in the context of organogold bonding and condensed phase gold cluster chemistry. The coherence of the exhibited chemistries demonstrates the value of this approach in examining novel transition metal cluster ion chemistry despite the potential for internal excitation of nascent laser-ablated cluster ions. This approach offers a means to prepare new heteronuclear clusters, including noble metal carbides, which may exhibit unique properties.
Dielectric etching for 0.18 μm technologies
Authors: Berruyer P. , Vinet F. , Feldis H. , Blanc R. , Lerme M. , Morand Y. , Poiroux T.
Published: July 2002

Two types of plasma source, high density plasma and magnetically enhanced reactive ion etching, have been compared on contact and vias etch process performances for 0.25 μm complementary metal–oxide semiconductor technology application. High density plasma is able to provide high oxide etch rate, low contact resistance and high yield on 350 nm contact size after etching. On the other hand, selectivity to photoresist is low and nonuniform across the wafer. Moreover, due to interaction between high density plasma and deep ultraviolet photoresist, striations are transferred on contact walls. Magnetically enhanced reactive ion etching is able to provide uniform etch rate and high selectivity to photoresist. Low contact resistance and high yield have also been obtained on 300 nm contact size after etching. The main disadvantage of this plasma source is the low oxide etch rate. Antenna effects due to contact opening have been evaluated on test structures. The results show a minimized induced damage effect for the high density plasma type reactor.
Doping of group III nitrides
Authors: Ploog Klaus H. , Brandt Oliver
Published: July 2002

Recent advances in the understanding of the origin of the notorious residual n-type conductivity in GaN and our new concept of co-doping for improved p-type conductivity in GaN are briefly reviewed. Our experimental data reveal that O from residual H2O, which substitutes N on lattice sites, is the origin for the observed n-type conductivity. Co-doping with Be and O to form donor-accepted pairs in GaN results in a strongly improved p-type conductivity at room temperature due to a substantial enhancement of the hole mobility. This concept has been independently confirmed by theoretical calculations.
Electrical, optical, and structural properties of indium-tin-oxide thin films deposited on polyethylene terephthalate substrates by rf sputtering
Authors: Kulkarni A. K. , Lim T. , Khan M. , Schulz Kirk H.
Published: July 2002

Indium-tin-oxide (ITO) is a transparent conducting material which is deposited as a thin film on glass substrates for use in opto-electronic devices. However, there are several applications for which ITO films on polymeric substrates are desirable. The sheet resistance, optical transmittance, and microstructure of as-deposited ITO thin films on unheated polyethylene terephthalate substrates were studied using rf sputter deposition. During separate deposition runs, the partial pressure of oxygen was varied from 5% to 20% and the deposition time was varied from 15 to 120 min. No significant variations are observed in the sheet resistance with respect to oxygen partial pressure; however, changes in sheet resistance were observed in ITO films deposited on different substrates for short deposition times (15 min). Additionally, the thickness of the film (assumed to be proportional to the deposition time) is shown to have a considerable impact on the sheet resistance and the optical transmittance. The x-ray diffraction data coupled with the sheet resistance data suggest that ITO films exhibiting a preferred (400) orientation have the highest sheet conductance. The changes observed in the sheet resistance, optical transmittance, and the refractive index due to the thickness of the film or oxygen partial pressure during deposition are explained on the basis of surface roughness, free carrier concentration, and the microstructure of the film.
Electron transport and emission properties of diamond
Authors: Yater J. E. , Shih A. , Abrams R.
Published: July 2002

The electron transport and emission properties of hydrogenated and cesiated single-crystal and chemical-vapor-deposited (CVD) diamond are investigated using secondary electron emission spectroscopy. The kinetic energy of the electrons and the height of the surface energy barrier are measured relative to the conduction band minimum, Ec, which is identified in the spectra. In spectra measured from hydrogenated and cesiated diamond surfaces, electron emission appears at energies E<Ec which gives direct evidence of a negative electron affinity. The strongest emission is observed from cesiated samples, which produced very high yields (δmax∼80–130 at Eb=2900 eV). The energy distributions from all three samples are sharply peaked at ∼0.50–0.65 eV above Ec and have a full width at half maximum ∼0.55–0.75 eV, except in the case of the cesiated CVD diamond samples. The energy distributions measured from cesiated CVD diamond are peaked at lower energy and are much broader due to lower emission-onset energies. An emission model, which invokes band bending near the surface, is deduced that accounts for the observed energy spectra from the samples in terms of the surface properties of the C(100) and CVD diamond and the internal electron energy distributions.
Residual stress in low pressure chemical vapor deposition SiNx films deposited from silane and ammonia
Authors: Temple-Boyer P. , Rossi C. , Saint-Etienne E. , Scheid E.
Published: July 2002

Varied SiNx films have been deposited by low pressure chemical vapor deposition from silane SiH4 and ammonia NH3 and the influences of the deposition parameters (temperature, total pressure and NH3/SiH4 gaseous ratio) on the film deposition rate, refractive index (assessed at a 830 nm wavelength), stoichiometry and thermomechanical stress are investigated and correlated. Low stress (≈600 MPa) Si3N4 films are obtained for the highest deposition temperature and the lowest total pressure but the gaseous ratio is shown to be the dominant parameter. According to the SiNx stoichiometry, silicon-rich silicon nitride and nitrogen-doped silicon (called NIDOS) depositions are obtained and compressive to tensile stresses are reported. A maximum in compressive stress is put into evidence for N/Si ratio roughly equal to 0.7 and is related to the cumulated effects of silicon nitridation and crystallization, characterizing the transition between nitrogen-doped silicon and silicon-rich silicon nitride. Finally, by considering stress, deposition rate, nonuniformity along the load and resistance to alkaline solutions, optimal (silicon-rich) silicon nitride deposition conditions are proposed for microelectromechanical applications.
Remote plasma etching of silicon nitride and silicon dioxide using NF3/O2 gas mixtures
Authors: Kastenmeier B. E. E. , Matsuo P. J. , Oehrlein G. S. , Langan J. G.
Published: July 2002

The etching of silicon nitride (Si3N4) and silicon dioxide (SiO2) in the afterglow of NF3 and NF3/O2 microwave discharges has been characterized. The etch rates of both materials increase approximately linearly with the flow of NF3 due to the increased availability of F atoms. The etch rate of Si3N4 is enhanced significantly upon O2 injection into the NF3 discharge for O2/NF3 ratios of 0.3 and higher, whereas the SiO2 etch rate is less influenced for the same flow ratios. X-ray photoelectron spectroscopy of processed Si3N4 samples shows that the fluorine content of the reactive layer, which forms on the Si3N4 surface during etching, decreases with the flow of O2, and instead oxidation and nitrogen depletion of the surface occur. The oxidation of the reactive layer follows the same dependence on the flow of O2 as the etch rate. Argon actinometry and quadrupole mass spectrometry are used to identify reactive species in the etching of both materials. The atomic fluorine density decreases due to dilution as O2 is added to the discharge. The mass spectrometer did not detect NFx species (x=1–3) at any discharge parameter setting, which indicates the near complete dissociation of NF3. Nitric oxide (NO) was detected by mass spectrometry, and the NO density shows the same dependence on O2 flow as the Si3N4 etch rate and the surface oxidation. Based on this observation, we propose that the etch rate enhancement for Si3N4 is due to the adsorption of the NO on the Si3N4 surface, followed by the formation of N2 with a N atom from the surface. The O atom can then attach to the same surface site, contributing to the oxidation.
Piezoelectric, dielectric, and interfacial properties of aluminum nitride films
Authors: Liufu D. , Kao K. C.
Published: July 2002

The piezoelectric and related properties of highly c-axis oriented AlN films fabricated by dc planar magnetron sputtering have been measured. Experimental results show that highly c-axis oriented AlN films can be fabricated by dc planar magnetron sputtering at low electric fields with energetic electrons driven out by a magnetic field to reduce any possible damaging effects resulting from electron bombardments on the growing films, and that the AlN films have a strong microwave piezoelectric effect. A microwave bulk acoustic wave delay line formed by depositing an AlN film as the transducer on a z-LiNbO3 substrate as the acoustic wave propagation medium exhibits good performances. The major advantage of such a delay line is that its weight and volume can be made much smaller than that of the conventional delay lines. The AlN films also have good chemical and dielectric properties, suitable for use as insulation or passivation layers.
Optical self-absorption technique for qualitative measurement of excited-state densities in plasma reactors
Authors: Miller Paul A. , Hebner Gregory A. , Jarecki Robert L. , Ni Tom
Published: July 2002

Measurements of excited-state populations in processing plasmas can be useful because those populations often are indicators of, or participants in, chemical reactions. An optical self-absorption technique has been used to measure the relative densities of species in long-lived excited states in high-density plasma reactors. The technique is advantageous because it is simple and inexpensive compared to many laboratory diagnostic techniques, and thus it has potential for industrial manufacturing applications. The technique is useful when absorption strength and wavelength are in acceptable ranges. This paper describes the technique, compares its performance to a more sophisticated laser-absorption technique, and presents self-absorption data from a laboratory reactor and from a 300 mm production-prototype reactor.
Kinetics of platinum silicide formation followed in situ by spectroscopic ellipsometry
Authors: Zhou S. M. , Hundhausen M. , Stark T. , Chen L. Y. , Ley L.
Published: July 2002

In situ ellipsometry is employed to study the kinetics of Pt silicide formation by thermal annealing with constant heating rates up to 30 K/min of a 10 nm platinum layer on silicon (100). From spectroscopic ellipsometry data of the initial Pt/Si, the intermediate Pt2Si, and the final PtSi phase an optimum photon energy of 3.5 eV was chosen for the kinetic study. Characteristic changes of the ellipsometric angles are observed as a function of temperature when the reaction fronts reach a depth below the surface that is related to the absorption length of the 3.5 eV photons. From an analysis of these transition temperatures based on the Kissinger formalism the activation energies for the formation of Pt2Si and PtSi are obtained as 1.55±0.05 and 1.72±0.05 eV, respectively, where the error bars follow from the precision of our measurements. A comparative study for a 100 nm Pt layer on Si yields the same activation energies albeit with a higher uncertainty, indicating that this method is particularly suited for ultrathin silicides.