bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of particle formation in the sputtering and reactive ion etching of silicon
Authors: Yoo W. J. , Steinbrüchel Ch.
Published: July 2002

Particle formation from a Si substrate in an Ar sputtering plasma and a reactive ion etching plasma of 10% CCl2F2 in Ar has been investigated by laser light scattering. The kinetics of particle growth are studied as a function of rf power and chamber pressure. Threshold behavior for particle generation has been observed in that minimum values of both rf power and pressure are necessary for particles to appear. In both reactive ion etching and sputtering, the smallest particles detected on the wafer are ∼0.2 μm in size. In sputtering most particles are spherical and must have been deposited onto the substrate from the plasma. On the other hand, in reactive ion etching most particles are hemispherical or conical and seem to have grown on the substrate itself. Particle formation is correlated with significant redeposition in sputtering and with deposition of a surface film in reactive ion etching. Si atoms removed from the substrate are probably responsible for the nucleation of particles in both types of plasmas because particle formation is much slower, yet the etch rate is much higher, in reactive ion etching compared to sputtering.
Dielectric and chemical modifications in polyimide films etched in O2/CF4 plasmas
Authors: Wu Shien-Yang , De Souza-Machado Ressano , Denton Denice D.
Published: July 2002

The effects of a reactive ion etching (RIE) plasma on the dielectric properties and chemistry of polyimide (PI) films are investigated. DuPont PI-2555, PI-2566, and PI-2611 are characterized before and after treatment in an O2/CF4 RIE (13.56 MHz) plasma. The capacitance and the dissipation factor of Al–PI–Al capacitors before and after etching are measured in a frequency range from 12 Hz to 100 kHz at relative humidity (RH) values of 5% and 85%. Debye-type dielectric relaxations are observed at 85% RH in all three materials investigated after treatment in an O2/CF4 plasma. The locations of the loss peaks are found to be dependent on the PI type and inlet gas CF4/O2 ratios. Electron spectroscopy for chemical analysis is used to monitor the chemical changes in PI due to plasma treatment, and the observed chemical and dielectric changes are correlated.
Performance of an ultrahigh-vacuum sample transfer system for investigation of molecular-beam epitaxy grown semiconductor surfaces
Authors: Wang X.-S. , Huang C. , Bressler-Hill V. , Maboudian R. , Weinberg W. H.
Published: July 2002

This article describes the performance of a sample transfer system which allows direct coupling between a molecular-beam epitaxy (MBE) chamber and several ultrahigh vacuum surface characterization chambers. The transfer system is simple, compact, and easily adaptable to any MBE or surface analysis chamber. By using this transfer system, high quality III–V compound semiconductor samples are routinely achieved, as judged by the scanning tunneling microscopy images obtained on these surfaces.
Deposition rates in direct current diode sputtering
Authors: Stutzin G. C. , Rózsa K. , Gallagher A.
Published: July 2002

A physical model for anode deposition rates in parallel-plate, dc-diode sputtering is presented and tested. The deposition rate has been measured as a function of the discharge voltage, the anode–cathode gap and the pressure, using silicon or molybdenum cathodes with argon. Deposition rates as high as 23 Å/s were obtained using 3 kV, and it is shown that deposition efficiency is similar to that obtained with magnetrons. The deposition rate varies inversely with anode–cathode gap at constant pressure and voltage and almost linearly with power density for discharge voltages above a threshold which depends on the cathode material. These observations are explained by the model, which can be used to estimate the deposition rates for any cathode material and gas for which the ion sputtering yields are known. Potential advantages and complications of dc diode sputtering for thin film deposition are discussed, and optimum conditions for high, uniform deposition rates are described.
Composition effects in ‘‘flash’’ evaporated CuIn(SexTe1−x)2 films
Authors: León M. , Díaz R. , Rueda F.
Published: July 2002

Thin films with composition around CuInSeTe and CuInSe1.5Te0.5 have been deposited by ‘‘flash’’ evaporation. The structural, electrical, optical, and surface [x-ray photoelectron spectroscopy (XPS) measurements] properties have been determined. Chalcogen content is always lower than 50% and crystallinity is higher when Se content increases. The samples always show p-type conduction even when the defect of chalcogen is 5% with resistivities in the 0.5–8.6 Ω cm range. The energy gap is in the 0.81–1.11 eV range. XPS measurements indicate that, after exposure to air, only the Te species presents two oxidation states preventing oxidation of the remaining elements. These properties are analyzed in terms of indium segregation at grain boundaries, anion vacancies, and cation disorder in the samples.
Formation and characterization of epitaxial phthalocyanine and perylene monolayers and bilayers on Cu(100): Low-energy electron diffraction and thermal desorption mass spectrometry studies
Authors: Schuerlein T. J. , Armstrong N. R.
Published: July 2002

Ordered monolayer and multilayer thin films of copper phthalocyanine (CuPc) and perylene dicarboxylic dianhydride (PTCDA) have been grown on Cu(100) single crystals. CuPc grows in a commensurate square lattice configuration, with two equivalent domains consisting of closest packed, flat lying Pc rings, rotated at ±21.8° from the principle Cu(100) axes. The dimensions of these square lattices (b1=b2=13.7 Å) are comparable to those observed using other substrates which interact weakly with the Pc overlayer (layered metal dichalocogenides, cleavage faces of single-crystal salts). PTCDA grows in a commensurate rectangular lattice (5√2×4√2)-R=45°, whose dimensions (b1=14.5 Å, b2=18.1 Å) are significantly different than those seen on weakly interacting substrates. Low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, and thermal desorption mass spectroscopy (TDMS) data for the adsorption of this molecule strongly suggest that the first monolayer is dissociatively adsorbed to the Cu(100) surface. Growth of ordered layers of PTCDA has also been carried out on a Cu(100) surface modified with 1–2 ML (monolayers) of an ordered CuPc film. LEED and TDMS data indicate the formation of a new commensurate rectangular unit cell (b1=13.7 Å, b2=20.5 Å) for these PTCDA/CuPc/Cu(100) overlayers, which suggest that the CuPc layer controls the architecture of the subsequent PTCDA layers. The formation of a wide range of highly ordered organic heterojunctions appears to be possible, starting with a strongly adsorbed first layer, on surfaces such as single-crystal metals.
Effects of substrate on ultrathin films of poly(γ -benzyl-L-glutamate) by scanning probe microscopy
Authors: Musselman I. H. , Smith D. L. , Enriquez E. P. , Guarisco V. F. , Samulski E. T.
Published: July 2002

Monolayer and bilayer Langmuir–Blodgett films of poly(γ-benzyl-L-glutamate) (PBLG) were prepared on highly oriented pyrolytic graphite (HOPG), mica, silicon, and glass. The films were imaged by atomic force microscopy (AFM) in the contact and tapping modes to develop imaging strategies for ultrathin polypeptide films and to assess the effect of substrate on film microstructure. A better understanding of the local polypeptide film structure could guide future methods of device fabrication. The AFM tapping mode enables long-term nondestructive imaging of PBLG mono- and bilayers for dimensions as small as 0.2 μm. In contrast, contact mode AFM readily damages PBLG films. PBLG has the best monolayer coverage on HOPG, although film is sometimes observed on each of the other three substrates. On HOPG, the monolayer has a predominantly ‘‘lacey’’ structure whereas for the hydrophilic substrates, mica, silicon, and glass, it is ‘‘banded’’ or ‘‘solid.’’ HOPG rarely exhibits a continuous bilayer film whereas the other three substrates exhibit much better coverage as bilayers than as monolayers. The PBLG monolayer behaves as a banded template for bilayer formation in some areas of mica, and for all four substrates, the second layer appears to be oriented with respect to the first. The morphology and coverage of PBLG as a function of substrate is discussed in terms of hydrophilicity and forces of adhesion. Whether voids observed by AFM in the PBLG structures are present in the native film at the air–water interface of the Langmuir trough, or are induced by film transfer, remains undetermined.
Computer-centric rotational depth profiling
Authors: Engle P. D. , Geller J. D.
Published: July 2002

Rotational depth profiling (RDP), also known as Zalar rotation [A. Zalar, Thin Film Solids 124, 223 (1985)], has been demonstrated by several groups [N. Veisfeld and J. Geller, J. Vac. Sci. Technol. A 6, 2077 (1988); E. Cirlin, J. Vajo, R. Doty, and T. Hasenberg, ibid. 9, 1395 (1991); E. Cirlin, Y. Cheng, P. Ireland, and B. Clemens, Surf. Interface Anal. 15, 337 (1990)] to eliminate the loss of depth resolution in multilayered materials by preventing ion sputter induced roughening. It is thought that the constantly changing angular orientation between the ion beam and the microcrystalline structure of the specimen evens out small differences in sputtering rates due to preferred orientation effects. The mechanical requirements for RDP are simple. The specimen is ion sputtered while it is rotating with the electron beam placed on the rotation axis. Published works to date involving RDP have been accomplished by placing the area to be profiled on the rotation axis. In practice, the runout or wobble of the rotation axis and the size of the electron beam determines what area is actually analyzed. It is very difficult to analyze areas less than (100 μm)2 [J. D. Geller and N. Veisfeld, Surf. Interface Anal. 14, 95 (1989)] without manually repositioning the specimen after each rotation and sputtering cycle. By automating the X, Y, and rotation manipulator axes, randomly selected areas to ∼10 μm in size can be depth profiled without regard to the location of the rotation axis and without the need for operator repositioning of the specimen. Mathematical derivations of the rotation calculations, actual performance of the computer controlled manipulator, and practical applications are discussed.
Properties of chemical vapor infiltration diamond deposited in a diamond powder matrix
Authors: Panitz Janda K. G. , Tallant David R. , Hills Charles R. , Staley David J.
Published: July 2002

Densifying nonmined diamond powder precursors with diamond produced by chemical vapor infiltration is an attractive approach for forming thick diamond deposits that avoids many potential manufacturability problems associated with predominantly chemical vapor deposition (CVD) processes. We have developed two techniques: electrophoretic deposition and screen printing, to form diamond powder precursors on substrates. We then densify these precursors in a hot filament assisted reactor. Analysis indicates that a hot-filament-assisted chemical vapor infiltration process forms intergranular diamond deposits with properties that are to some degree different from predominantly hot-filament-assisted CVD material.
Sputtering yield of optical materials: Sigmund’s model and experimental results
Authors: Scaglione S. , Caneve L. , Sarto F.
Published: July 2002

The main drawback of the ion beam assistance during optical thin film deposition is the stoichiometry alteration due to the different sputtering yield of elements which compose the film itself. In optical materials such effect causes both an increase of absorption coefficient and undesirable variation of refractive index. In order to maintain the advantages of the ion beam assistance (i.e., enhancement of adhesion, compactness, good control of optical properties) the sputtering phenomena should be modeled to recognize the parameters of the ion beam (energy, angle of incidence, and ion mass) that minimize the stoichiometry alteration. The Sigmund’s model is an analytical approach widely used to treat the modelling of the sputtering phenomenon. In this work the Sigmund’s model was applied to fit the experimentally measured sputtering yield of several materials typically employed to fabricate optical coatings: silicon dioxide (SiO2), yttrium oxide (Y2O3) and zinc selenide (ZnSe). The yield measurements were performed both at different angle of incidence of the beam (0°, 45°) and with different bombarding ion mass and energy. The experimental results appear well fitted by the relation of the sputtering yield (Sigmund’s model) at all considered angles and ion masses. Sputtering yields of the material components as for instance silicon (YSiion) and oxygen (YOion) for SiO2 material, were modeled as well as their behavior with either ion energy or ion mass.
Determination of the ion velocity in a radio frequency ion beam by laser-induced fluorescence
Authors: Brockhaus A. , Yuan Y. , Engemann J.
Published: July 2002

Laser-induced fluorescence (LIF) has been used to measure in situ the velocity of argon ions being extracted from a filamentless capacitively coupled radio frequency ion beam source. Velocity distributions are measured by scanning a narrow-bandwidth dye laser over the Doppler-shifted absorption profile of an Ar II line while detecting the fluorescence. In the ion beam, charge–exchange processes produce a group of low energy ions manifested in an unshifted LIF peak useful for wavelength calibration. Partial reflection of the laser beam gives rise to additional LIF signals with a negative wavelength shift, thereby generating a mirror image of the originally measured ion velocity distribution. The ion velocity distribution has also been independently obtained with an electrostatic retarding field analyzer (RFA). The broad ion beam is characterized by an energy spread of about 20 eV and a mean energy between 100 and 1000 eV, depending on the extraction optics and its parameters. LIF results are compared with the RFA measurements and show excellent agreement.
Structure and composition of hydrogenated TixCy thin films prepared by reactive sputtering
Authors: Delplancke M. P. , Vassileris V. , Winand R.
Published: July 2002

Thin films of hydrogenated titanium carbide are prepared by reactive magnetron direct current sputtering in mixed atmospheres of argon and methane or argon and acetylene. The deposition process is followed on line by optical emission spectroscopy. The films are characterized by various techniques: scanning electron microscopy, transmission electron diffraction and microscopy, x-ray diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The influence of the gas phase composition and the current density on the structure and composition of the films is examined. The morphology and crystallinity of the deposits are strongly dependent on the carbon content in the films. The presence of an amorphous carbon phase results in a decrease of the TiC grain size. The proportion of Ti–C bonds in the films is correlated to the decomposition of the carbon precursor in the discharge, as shown by optical emission spectrometry, and to the composition of the target surface in these conditions. This is especially strong in the case of C2H2–Ar mixtures. A comparison of the two carbon precursors is presented.
General geometry calculations of one-stage molecular flow transmission probabilities for turbomolecular pumps
Authors: Katsimichas S. , Goddard A. J. H. , Lewington R. , de Oliveira C. R. E.
Published: July 2002

In this paper the pumping mechanism of a single stage of a turbomolecular pump (TMP) is addressed. A collisionless gas, a Maxwellian distribution of particles at the inlet and outlet surfaces of the passage, and diffuse reflection for the particles that collide with the walls of the passage are assumed. Models of this type have, until now, only been applied to the two-dimensional (2D) case, i.e., the TMP stage was approximated by an infinite row of blades. This approximation can only be valid for very narrow passages, far from the axis of rotation. In the present work the 2D case has been assessed in detail as a basis for confidence in three-dimensional (3D) modeling. The main difficulties in modeling the 3D case arise from the geometric complexity and the rotating frame of reference. As a result of the latter, particle orbits are no longer straight lines, and their intersection with the walls has to be calculated iteratively. The Monte Carlo method was chosen to model the 3D case as it appears to have significant advantages. The passage is divided into layers normal to the axis of rotation, and a particle proceeds at every time step to the next or previous layer. This technique of tracking saves computer time as it takes advantage of certain characteristics of the rotational system. Results for different types of blade passages are presented.
Quantitative analysis of borophosphosilicate glass films on silicon using infrared external reflection–absorption spectroscopy
Authors: Franke James E. , Zhang Lizhong , Niemczyk Thomas M. , Haaland David M. , Radigan Kenneth J.
Published: July 2002

Borophosphosilicate glass (BPSG) dielectric thin films deposited on both bare and oxide-coated undoped silicon wafers have been analyzed using infrared external reflection–absorption spectroscopy (IRRAS). The partial least-squares (PLS1) algorithm was used to simultaneously determine boron content, phosphorous content, and film thickness, with standard errors of prediction of 0.08 wt %, 0.11 wt %, and 24 Å, respectively, in the BPSG films on oxide-coated wafers (similar results were obtained with the bare wafer BPSG sample set). These results were statistically equivalent to the precisions of the reference methods used to determine each BPSG property, indicating that the precisions of the PLS1 models were limited by the precisions of the reference methods. IRRAS reproducibility and repeatability results verified that the method can be more precise than the reference methods. The reproducibility results were derived from the standard deviation of ten PLS1 predictions of ten IRRAS spectra that were obtained from a single BPSG sample that was moved in and out of the sample chamber between each spectral measurement. The repeatability results were obtained similarly, but the sample was not moved between acquiring the ten spectra. The precision of the IRRAS method from the repeatability data was found to be ±0.006 wt % B, ±0.011 wt % P, and ±4 Å film thickness. The reproducibility results were generally less precise than the repeatability results. Studies done as a function of spectral resolution and signal averaging showed that very rapid IRRAS measurements could be made (up to 2 Hz) with high PLS1 prediction precision for the three calibrated BPSG properties. The results show that the IRRAS technique has great potential for rapid, at-line quality control monitoring of BPSG thin films on undoped silicon wafers.
Vacuum gauging with complementary metal–oxide–semiconductor microsensors
Authors: Paul O. , Brand O. , Lenggenhager R. , Baltes H.
Published: July 2002

We report different types of vacuum microsensors (size <500 μm). The devices were fabricated with a standard complementary metal–oxide–semiconductor integrated circuit process followed by silicon bulk micromachining or surface micromachining. Two sensors are thermal, and a third type is resonant. Their pressure response results from the pressure dependent dissipation of energy or momentum to the surrounding gas. Different designs with sensitive ranges from 1 to 106 Pa are demonstrated. The sensor responses are modeled using kinetic gas theory, with the conclusion that a typical dissipation length defined by the device geometry determines the useful pressure range.
Photoelectron spectroscopy during pulsed laser melting of surfaces
Authors: Gantner G. , Boyen H.-G. , Oelhafen P. , Rink K.
Published: July 2002

A method to perform photoelectron spectroscopy (PES) on systems at high temperatures and with a high saturation vapor pressure is presented. The basic concept consists of a time-resolved data acquisition following pulsed laser heating and melting of the sample surface. With this technique it is possible to get access to samples under conditions which normally would not be compatible with the requirements of PES. A standard electron spectroscopy for chemical analysis spectrometer has been equipped with additional electronics to allow time-resolved measurements. A small spot monochromated x-ray photoelectron spectroscopy source is used for the core-level spectroscopy and a modified gas discharge lamp for excitation of the valence band. The first results of valence-band spectra taken with this method are shown for germanium and silicon and its feasibility even in core-level spectroscopy is shown in the case of germanium.
Effect of energetic particles on the residual stresses in nonhydrogenated amorphous carbon films deposited on grounded substrates by dc magnetron sputtering
Authors: Mounier E. , Pauleau Y.
Published: July 2002

Amorphous carbon (a-C) films have been deposited on grounded silicon substrates by magnetron sputtering from a graphite target in pure argon discharges. The characteristics of the magnetron discharge were determined by Langmuir probe measurements as functions of the argon pressure and sputtering power. The flux and energy of argon ions impinging on the grounded substrates were deduced from Langmuir grid probe measurements. The flux of carbon atoms condensed on Si substrates was obtained from Rutherford backscattering spectroscopy measurements. The residual stresses in a-C films were found to be dependent on the argon pressure. The average kinetic energy of carbon atoms ejected from the target was determined from the energy distribution calculated from the model proposed by Thompson. The kinetic energy of carbon atoms condensed on the film surface was determined on the basis of calculation developed from the kinetic gas theory. The intensity of the intrinsic stress developed in a-C films was correlated to the flux and energy of neutral carbon atoms and argon ions impinging on the surface of growing films. The dependence of the intrinsic stress on the energetics of the deposition process matched the prediction deduced from the model of Windischmann.
Molecular beam sampling to analyze the reaction mechanism of chemical vapor deposition
Authors: Tsutsumi Y. , Ikegawa M. , Usui T. , Ichikawa Y. , Watanabe K. , Kobayashi J.
Published: July 2002

In order to understand the chemical vapor deposition (CVD) reaction mechanism, forming a thin film from the gas phase, it is important to identify the intermediate chemical active species (radicals) for each reaction. Radicals generally have very short lifetimes; therefore, it is very difficult to detect them. Molecular beam sampling (MBS) is a method that can extract radicals in the gas phase using free jet expansion. A vacuum system using a MBS method was designed to analyze the CVD reaction mechanism in the gas phase near the surface of the wafer. The system consists of a thermal flow-through type CVD reactor and three differential pumping vacuum chambers with a quadrupole mass analyzer. The performance of the MBS system was tested with various gases. The system was applied to detect radicals produced in the region near the wafer in a thermal TEOS/O3 (tetraethylorthosilicate) CVD reaction to deposit SiO2 thin films. It is proved that the radicals, from which ethoxy bases of TEOS are extracted, are formed in the gas phase and can play an important role in the thermal TEOS/O3 CVD reaction.
Microtribological studies of unlubricated and lubricated surfaces using atomic force/friction force microscopy
Authors: Koinkar Vilas N. , Bhushan Bharat
Published: July 2002

Microtribological studies were performed on unlubricated and lubricated (Z-15 and Z-DOL with hydroxyl end groups) silicon, double grafted C18 layer, Langmuir–Blodgett (LB) film, gold film and mica samples in ambient, dry nitrogen and dry air environments using atomic force/friction force microscopy (AFM/FFM). A sharp tip of AFM/FFM sliding on a surface simulates a single asperity contact. The silicon samples lubricated with Z-15 and Z-DOL lubricant films exhibit lower coefficient of microfriction than that of the unlubricated silicon sample. Microfriction values are lower than that of the macrofriction. Ploughing contribution is responsible for the higher macrofriction values. The microfriction experiments on bare silicon and lubricated with Z-15 and Z-DOL carried out in dry nitrogen and dry air exhibit lower coefficient of microfriction values than those in ambient atmosphere measurements. Dewetting of the liquid film in a humid environment is believed to be responsible for higher microfriction. The dependence of scanning velocity on microfriction was studied and it was found that the friction force decreases with an increase in the scanning velocity for the liquid-lubricated samples in the humid environment and it is relatively insensitive to scanning velocity in dry environments. Alignment of liquid molecules (shear thinning) is believed to be responsible for the drop in microfriction at high scanning velocities. Micro- and nanowear tests reveal that the chemically bonded Z-DOL lubricant is more durable than the Z-15, double grafted C18, LB and gold films.
Solid phase epitaxy with x-ray irradiation using a compact synchrotron radiation source AURORA
Authors: Katoh Takanori , Yamada Hironari , Sato Fumio , Hirano Yoshiyuki , Chikawa Jun-ichi
Published: July 2002

Solid phase epitaxy from the 0.2-μm-thick amorphous Si films, which were made by As ion implantation, was achieved by exposure to synchrotron radiation at a distance of 0.75 m from a compact synchrotron radiation source AURORA. The substrate temperature during this process was below 430 °C, not enough for thermal crystallization. We found the photon flux threshold for this x-ray assisted crystallization to be 5×1015 photons/s mm2. The threshold may be due to the transition from the diffusion-limited rate to the reaction-limited rate for the annihilation of the vacancies to form the crystal. The L-shell excitation may play a more important role than the K-shell excitation in this case.
Physical properties and chemical states of rf sputter deposited SiWOx films
Authors: Shibata Itaru , Nishide Toshikazu , Hasegawa Toshinori
Published: July 2002

Tungsten oxide films containing silicon oxide (SiWOx) as solar control materials were deposited by rf sputtering using Si10W90 and Si50W50 targets. The resistivity and transmittance in the near-infrared region of all the films increased as the O2/Ar ratio increased. Resistivities from 0.86 Ω cm to 2.27×104 Ω cm were obtained depending on the target used and O2/Ar ratio. The oxidation states of tungsten in the films were estimated by curve fitting XPS spectra. When the films were deposited using a target with a smaller amount of Si (Si10W90), the chemical state of W was similar to that in WOx films. However, lower and novel chemical states of W (W5+, W4+, and W3+) were present when the films were deposited using a target with a larger amount of Si (Si50W50).
Relating electric field distribution of an electron cyclotron resonance cavity to dry etching characteristics
Authors: Ko K. K. , Pang S. W. , Dahimene M.
Published: July 2002

The electric field distribution for an electron cyclotron resonance (ECR) cavity was measured using microcoaxial probes. Typically, two to three resonant modes are found for each plasma condition and longer cavity length provides a more stable plasma. A 30° periodicity is seen in the angular dependence of the electric field, and the peak right across the microwave input probe becomes more dominant at shorter cavity length. The longitudinal dependence of the electric field has a peak close to the middle of the cavity, and the measured field patterns agree well with the theoretical prediction. The resonant modes were identified by fitting the experimental measurements to linear combinations of electromagnetic resonant modes with characteristic length close to the cavity height. Using this method, all the modes in this ECR cavity were found to be multimode, and the resonant mode with the longest cavity length was found to be a mixing of TE314 and TE611 modes. Significant changes in the electric field patterns are seen when the ECR cavity is out of tune. The sensitivity of electric field distribution to ECR cavity tuning allows process control to be implemented by monitoring the changes in the electric field intensity of just a single probe position. Despite the variations in electric field distribution for different resonant modes, uniformity of photoresist etching across 15-cm-diam wafer is better than 5%. The good uniformity of the photoresist etching suggests that the plasma density at the wafer is uniform, probably due to the diffusion of the reactive species from the ECR source.
Near edge x-ray absorption fine structure investigation of the orientation and thermally induced order–disorder transition in thin organic films containing long chain hydrocarbons
Authors: Schertel A. , Hähner G. , Grunze M. , Wöll Ch.
Published: July 2002

The thermally induced structural changes in Langmuir–Blodgett films of Ca-arachidate with one and nine layer thicknesses and those in self-assembled monolayers of alkanethiols were investigated systematically between 300 and 410 K using near edge x-ray absorption fine structure (NEXAFS) spectroscopy. With increasing temperature the initial strong linear NEXAFS dichroism reflecting the high degree of orientational order within the films decreases continuously and vanishes above 390 K. In addition, the spectra recorded for elevated temperatures (above 400 K) show a peak splitting of the prominent R* resonance at 287.7 eV which is attributed to changes in the electronic structure of the alkane chains caused by thermally induced structural defects, i.e., gauche conformations. The intensity of this new feature increases exponentially with temperature and allows one to extract an energy of 46 kJ/mol (480 meV) for the creation of a gauche conformation in densely packed hydrocarbon films.
Morphology and phase of tin oxide thin films during their growth from the metallic tin
Authors: Chung Y. S. , Hubenko A. , Meyering L. , Schade M. , Zimmer J. , Remmel T.
Published: July 2002

Thin tin films were deposited on oxidized silicon substrates by sputtering. Changes in both the phase and morphology of the films were studied as a function of the annealing process, time and atmosphere. X-ray diffraction (XRD) analysis was used to study phase evolution of the films during annealing. Atomic force microscopy and scanning electron microscopy were employed to characterize microstructure and morphology of the films. XRD analyses revealed phase transformations from metallic Sn to romarchite and finally to cassiterite as a function of higher annealing temperature. Differences in the phase transformation rate from metallic tin films to tin dioxide were observed between oxygen and air atmospheres. Little variation in grain size was observed during oxidation annealing from metallic to oxide states in either air or oxygen. However, surface roughness of the films was strongly dependent on the annealing atmospheres. The films annealed under air showed that surface roughness increased linearly with time and temperature, while the surface roughness change of the tin oxide films annealed under oxygen exhibited saturation behavior. The surface morphology change of the tin oxide films processed in oxygen exhibited different behavior from those processed in air.
In situ diagnostic studies of reactive co-sputtering from two targets by means of soft x-ray and optical emission spectroscopy
Authors: Nyberg T. , Skytt P. , Gålnander B. , Nender C. , Nordgren J. , Berg S.
Published: July 2002

Fabrication of electronic and optical devices involves synthesis of tailor-made materials with complex composition. Reactive co-sputtering from two targets is a suitable process for fabrication of, e.g., a two-element nitride compound material. The composition of the two-element compound, however, is strongly dependent on different processing parameters. It is therefore of great importance to understand and study how the processing parameters influence the composition of the deposited film. In this article we present studies of the film composition in reactive co-sputtering of titanium and vanadium nitride. In order to determine the film composition during film growth we have applied in situ soft x-ray emission and optical emission spectroscopy. The experimental findings are compared with ex situ elemental analysis and predictions from computer simulations of the reactive sputtering process. The experimental results agree qualitatively with the results from the simulations. Our findings also illustrate the complexity of the reactive co-sputtering process.
Influence of growth conditions on the residual strain in thick metalorganic vapor phase epitaxy grown InGaAs epilayers
Authors: Maigné P.
Published: July 2002

The residual elastic strain has been measured in thick (≈2 μm) InxGa1−xAs (0.07<x<0.14) layers grown on GaAs substrates at a temperature of 625 °C and a growth rate of 1μm/h. X-ray diffraction experiments show that the residual strain represents 15% of the lattice mismatch. This result cannot be explained by the difference in thermal expansion coefficients between the substrate and epilayer, but can be qualitatively explained by a reduction of the effective stress due to repulsive interaction between dislocations. The effects of growth conditions on the extent of strain relief have also been studied and it was found that increasing the growth temperature from 625 to 670 and 680 °C does not significantly change the residual strain. On the other hand, the residual strain can be reduced to 5% or increased to 33% of the lattice mismatch by lowering the growth rate from 1 to 0.45 μm/h or by increasing the growth rate from 1 to 2 μm/h, respectively. This change is related to the variation of the growth time, since a post-growth anneal for 1 h at growth temperature of a sample grown at 1 μm/h leads also to the same reduction of the residual strain as when grown at lower rates. This shows that for thick layers, the relaxation process is not completed when the growth is interrupted and suggests that despite the strong reduction of the effective stress, the dislocations are still mobile.
Growth mechanism of 3C–SiC(111) films on Si using tetramethylsilane by rapid thermal chemical vapor deposition
Authors: Seo Y. H. , Nahm K. S. , Suh E.-K. , Lee H. J. , Hwang Y. G.
Published: July 2002

We have used a rapid thermal chemical vapor deposition technique to grow epitaxial SiC thin films on Si wafers by pyrolyzing tetramethylsilane (TMS). The films were observed to grow along the (111) direction of 3C–SiC at temperatures above 1000 °C. The quality of the films was significantly influenced by the TMS flow rate in the gas mixture, the growth temperature, and the gas pressure in the reactor. Single-crystal SiC films were grown at TMS flow rates below 1.0 sccm with a H2 carrier gas flow rate of 100 sccm. The gas pressure in the reactor has a great influence on the crystallinity, morphology, and thickness of the SiC film grown. Gas phase analyses indicated that TMS dissociates into hydrogen, silicon atoms, and hydrocarbons such as CH4, C2H2, and C2H4 at the growth temperature. The chemical composition of the grown films was analyzed. The growth mechanism of the SiC film on the Si substrate without the carbonization process is discussed based on the experimental results.
Tunable diode laser spectroscopy measurement of CH3 and C2H2 densities in a H2O/CH3OH radio frequency chemical vapor deposition diamond system
Authors: Kim Suchan , Billesbach D. P. , Dillon R.
Published: July 2002

We present preliminary results from our methanol–water plasma system using a radio frequency (rf) discharge reactor without a substrate. Second-harmonic, tunable diode laser absorption spectroscopy (TDLAS) was used to detect the number densities of the dilute molecular species, CH3 and C2H2. TDLAS was also used to measure the dissociation fractions of CH3OH and H2O. The plasma pressure was 1.0 Torr, and the molecular density fraction, [CH3OH]/[CH3OH+H2O], was 0.6 to give the atomic ratio of C, H, and O most favorable for diamond film growth. We found that about 73% of the water was dissociated with 1500 W of rf power while more than 98% of the methanol was dissociated with only 500 W of power. The CH3 and C2H2 concentrations gradually increased with rf power up to 900 W. The ranges of the number densities were 0.56×1012/cm3–4.34×1012/cm3 for CH3 and 0.50×1013/cm3–3.18×1013/cm3 for C2H2. The number density of CH3 showed an abrupt decrease at 1000 W, while a sudden increase of C2H2 occurred at the same power. These sudden changes are due to a transition of the plasma from a low-density state plasma to a high-density, more localized state, caused by a change in the plasma coupling mechanism. This transition also occurs in the dissociation of water.
Study of oxidized cadmium zinc telluride surfaces
Authors: Chen K.-T. , Shi D. T. , Chen H. , Granderson B. , George M. A. , Collins W. E. , Burger A. , James R. B.
Published: July 2002

Cadmium zinc telluride has been developed as a room temperature radiation detector in recent years. The issue of decreasing surface leakage current, which affects the energy resolution of radiation response, was investigated extensively by various surface oxidation treatments. In this study, an aqueous solution of hydrogen peroxide (H2O2) was used in the oxidation of CdZnTe wafers in order to decrease surface leakage current. The surface chemical composition and its morphology modification due to this oxidation process were investigated. X-ray photoelectron spectroscopy analysis revealed that the main chemical species left after H2O2 oxidation are TeO2 along with a small amount of a Cd-related oxide. We found no obvious evidence of the presence of Zn-related oxides. The oxide thickness reaches a saturation after 5 min of H2O2 oxidation. The atomic force microscopy images revealed that, at this stage of saturation, the surface roughness and the mean diameter of the main features were about 1.3 μm and 97 nm, respectively. The decrease of 37% in the surface leakage current was related to the oxide layers formed by H2O2 oxidation.
Comparison of microstructural features of diamond composite coatings with polycrystalline diamond or boron nitride brazed on tungsten carbide tools
Authors: Jagannadham K. , Fan N. D. , Komanduri R. , Narayan J.
Published: July 2002

We have investigated microstructure and properties of diamond composite coatings on cemented tungsten carbide tool substrates, and compared wear resistance of these coatings with that of polycrystalline diamond (PCD) and polycrystalline boron nitride (PCBN) tools brazed on to cemented tungsten carbide substrates. The diamond composite coatings consist of layers of discontinuous diamond, TiC, and continuous diamond. In these composite layers, diamond is deposited by hot filament chemical vapor deposition and TiC by pulsed laser physical vapor deposition. Thermal stresses in the composite layer and the substrate are reduced and thereby help to improve the adhesion of diamond to the tool substrate. These tool coatings are characterized by scanning electron microscopy, Raman spectroscopy, secondary ion mass spectroscopy, and x-ray diffraction. The results of microstructural characterization and analysis of chemical composition are correlated with wear resistance. The present results demonstrate the advantages associated with composite diamond coatings compared to PCD and PCBN tool coatings.
Calibration of an axial symmetric transmission gauge in ultrahigh and extreme high vacuum
Authors: Akimichi H. , Arai T. , Takeuchi K. , Tuzi Y. , Arakawa I.
Published: July 2002

The sensitivity factor of an axial symmetric transmission gauge (AT gauge) was determined by the conductance modulation method (CMM) in the pressure range from 10−10 to 10−6 Pa. The gauge has a Bessel-box type energy filter between a Bayard–Alpert gauge type ionizer and an ion detector to eliminate the limiting factors of pressure measurement in extreme high vacuum such as the soft x-ray effect and the electron stimulated desorption of ions. The lower limit of the pressure measurement of the gauge is estimated to be about 10−12 Pa or lower. The sensitivity factor showed a slight pressure dependence caused mainly by outgassing from the gauge itself. The sensitivity factor of the AT gauge, which was further corrected for the effect of outgassing by the CMM, is almost constant in the pressure range from 10−10 to 10−6 Pa and is (2.3±0.1)×103 Pa−1 for hydrogen.
Low-energy broad beam electron gun
Authors: Barefoot Thomas W. , Ebinger Hans D. , Yates John T.
Published: July 2002

A low-energy electron gun for the energy range of 5–100 eV providing a uniform and high electron flux over a circular surface area of several cm2 has been designed and tested. Focusing elements allow one to vary the beam diameter according to experimental needs. The uniform current densities make it suitable for the study of electron stimulated surface chemistry and thin-film production.
Lattice curvature of InxGa1−xAs/GaAs [001] graded buffer layers
Authors: Romanato F. , Natali M. , Napolitani E. , Drigo A. V. , Bosacchi A. , Ferrari C. , Franchi S. , Salviati G.
Published: July 2002

Ion channeling analysis and x-ray diffraction reciprocal space maps have been performed on InxGa1−xAs buffer layers grown with different composition profiles on well-cut (001) GaAs substrates. On all of the samples analyzed we detect a curvature of the layer lattice, i.e., a tilt of the lattice with respect to the substrate which varies coherently along the sample surface. The layer tilt is directed inward defining a curvature that is concave, large (up to 2.5° cm−1) and that decreases when approaching the substrate. We describe this new phenomenon in terms of a coherent lateral distribution of the orientations of the misfit dislocation Burgers’ vectors.
Optical properties of low-density foams considered as targets for inertial confinement fusion
Authors: Glembocki O. J. , Rebbert M. L. , Prokes S. M. , Sethian J. D. , Marrian C. R. K. , Chan L. Y.
Published: July 2002

An optical method for measuring scattered light, namely by analyzing the transmitted light, is used to characterize the optical properties of low-density foams that are candidates as targets for inertial confinement fusion. This method allows us to simultaneously measure both scattering and intrinsic absorption in the foam. Three types of foams have been examined: two have similar chemistries and are based on either ethylene glycol dimetacrylate (EGDM) or trimethylolpropane trimethacrylate (TMPT). The other one is based on resorcinol formaldehyde (RF). We observe that while the RF foams are orange in color and nearly transparent, the EGDM/TMPT based foams are white and opaque. The opacity of these foams is shown to be due to light scattering by particles having dimensions on the order of 200 nm. In contrast, the light scattering from the RF foams indicates that the structures scattering light are on the order of 20 nm. The orange color of the RF foams is shown to be due to intrinsic absorption of light by the polymer comprising the foam. The onset of absorption is seen to shift towards the blue as the foams age. Index matching to the TMPT foam using ethanol is shown to significantly reduce the scattering.
Spectroscopic and thermal studies of a-SiC:H film growth: Comparison of mono-, tri-, and tetramethylsilane
Authors: Lee Moon-Sook , Bent Stacey F.
Published: July 2002

Thin a-SiC:H films were grown by hot-wire chemical vapor deposition at 200 K on Si(100) using mono-, tri-, and tetramethylsilane as single source precursors. The film structure and thermal reactivity were compared using in situ multiple internal reflection Fourier transform infrared spectroscopy and temperature programmed reaction/desorption. The results indicate that both mono- and trimethylsilane precursors yield films containing mixed silicon hydrides, SiHx (x=1–3), and mostly intact methyl groups. Tetramethylsilane did not lead to substantial film growth. These results are consistent with a mechanism for film growth involving Si–H bond cleavage. All the films are stable to above 550 K. By 600 K, silane and methylsilanes evolve, following the loss of terminal SiH3 and Si(CH3)xH3−x groups in the films. At higher temperatures, hydrogen desorption and hydrocarbon evolution are observed. For films grown with monomethylsilane, methane is the main hydrocarbon evolved, but films grown with trimethylsilane yield mainly acetylene. The production of acetylene is consistent with the higher concentration of methyl groups in the trimethylsilane films.
Dimer chain patterns during submonolayer growth of silicon on Si(100)
Authors: Iguain J. L. , Mártin H. O. , Aldao C. M. , Gong Y. , Chey S. J. , Weaver J. H.
Published: July 2002

Dimer chains formed during deposition of Si on Si(100)-2×1 at ∼435 K have been analyzed using scanning tunneling microscopy. Results are compared with the outcome of Monte Carlo simulations. The size distributions obtained from experiments and the model give new insight into the basic mechanisms responsible for dimer chain formation. For the Monte Carlo simulations, activation energies for adatom diffusion of 0.7 and 0.5 eV, parallel and perpendicular to dimer row directions, gave the best agreement with experimental results.
Solution of the outgassing equation for the pump down of an unbaked vacuum system
Authors: Akaishi K.
Published: July 2002

The outgassing equation based on the Temkin isotherm is applied to consider the outgassing behavior in the pump down of an unbaked vacuum system. A method to solve the equation approximately is discussed first, and then solutions of outgassing rates are derived. Solutions to the equation which can be used to predict the dependence of the outgassing rate on pumping time and pumping speed are discussed. The solutions finally obtained are able to explain the outgassing behavior observed experimentally for a 304 stainless steel chamber after exposure to moist air, in particular the dependence of the outgassing rate on time and pumping speed.