bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-temperature magnetoabsorption in HgTe/Hg0.15Cd0.85Te superlattices
Authors: Yoo K. H. , Aggarwal R. L. , Ram-Mohan L. R. , Wu O. K.
Published: July 2002

We report a study of magnetoabsorption in three HgTe/Hg0.15Cd0.85Te superlattices at room temperature. Three absorption peaks were observed and analyzed with our transfer-matrix method. With our initial choice of input parameters, we obtain a reasonable fit with a valence-band offset of 730 or 850 meV, depending on the sample. We discuss the effects of changes in some of the important input parameters on the superlattice Landau levels.
The growth and characterization of HgTe and HgCdTe using methylalylltelluride
Authors: Bhat Ishwara B. , Ehsani Hassan , Ghandhi Sorab K.
Published: July 2002

HgTe and HgCdTe layers have been grown by organometallic vapor phase epitaxy at low temperature by using methylallyltelluride (MATe), dimethylcadmium (DMCd) and elemental mercury. Use of MATe enabled the growth of layers in the 250–320 °C range, which is 50 °C lower than the growth temperature when diisopropyltelluride (DIPTe) is used, for the same growth rate. The layers were characterized by double crystal x-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, and by low temperature Hall measurements. Growth below 340 °C resulted in featureless HgTe layers. HgTe layers, grown on CdTe, are misoriented with respect to the substrate by about 60–150 arc s. This tilting was not observed when CdZnTe substrates, to which there is a better lattice match, were used. The high quality of low temperature grown HgTe is demonstrated by the very narrow (27 arc s) full width at half-maximum (FWHM) of x-ray diffraction for layers grown on CdZnTe substrates. HgCdTe layers, grown at 320 °C, showed well resolved interference fringes even for thin layers indicating the presence of an abrupt interface with the substrate. As grown layers were n-type, with the best mobility of 40 000 cm2 /V s at 40 K for a layer with composition x of 0.23.
Defects in ZnTe, CdTe, and HgTe: Total energy calculations
Authors: Berding M. A. , van Schilfgaarde M. , Paxton A. T. , Sher A.
Published: July 2002

Total energies for various impurities and defects in HgTe, CdTe, and ZnTe are calculated. Calculations were done using a self-consistent linear muffin-tin orbital (LMTO) method within the local density and atomic spheres approximation. We calculate the total energy for substitution on both lattice and interstitial sites, and estimate the lattice strain energies. Estimates of the variation with the alloy predict a linear variation of the substitution energy with the local concentration. We predict that the Te antisite will be more prevalent in all three of the compounds than previously thought. The problem of cross doping during heteroepitaxy on GaAs is predicted to be greater on the cation sublattice.
CdTe(110) interface formation with reactive and nonreactive overlayers: Al, Ti, Pd, Ag, Au, In, and Ce
Authors: Trafas B. M. , Meyer H. M. , Aldao C. M. , Siefert R. L. , Vos M. , Xu F. , Weaver J. H.
Published: July 2002

High resolution synchrotron radiation photoemission has been used to investigate room temperature interface formation involving CdTe(110) and transition metals (Ti), noble and near-noble metals (Ag, Au, Pd), lanthanide metals (Ce), and simple metals (Al, In). Core level and valence band results reveal substrate interactions with quite different chemical behavior and morphologies. Deposition of Ag and In at 300 K produces a nondisrupted substrate on which clusters form spontaneously. Deposition of Al, Ti, and Ce produces metal–anion reactions and substrate disruption at low coverage, with metal clusters that grow on the reacted layer after reaction has been curtailed by kinetic considerations. For Pd and Au, there is substrate disruption, even though the heats of formation for Pd and Au tellurides are smaller than CdTe, and there is segregation to the surface for both Cd and Te atoms. Studies of Au overlayers formed on reacted Ti interlayers on CdTe show changes in Cd atom distribution and give insight into the stability of these interfaces.
Backside secondary ion mass spectrometry investigation of ohmic and Schottky contacts on GaAs
Authors: Schwarz S. A. , Palmstro/m C. J. , Schwartz C. L. , Sands T. , Shantharama L. G. , Harbison J. P. , Florez L. T. , Marshall E. D. , Han C. C. , Lau S. S. , Allen L. H. , Mayer J. W.
Published: July 2002

A backside secondary ion mass spectrometry (SIMS) technique is employed to examine seven distinctive metallic contacts on GaAs at various stages of formation. The contacts are formed on multilayered GaAs/AlGaAs structures grown by molecular beam epitaxy (MBE), each containing an AlGaAs etch-stop layer and AlGaAs marker layers for precise alignment of the SIMS depth profiles. After removal of the substrate, the contact structures are profiled from the backside to avoid depth resolution degradation, which results when sputtering through a nonuniform multilayered metallic contact. The seven contacts examined are TaSix, Au/Ge/Ni, Au/Ge/Pd, Ge/Pd, Si/Pd, In/Pd, and Si/Ni/Mg. The TaSix Schottky contact exhibits extensive interdiffusion. The Au/Ge/Ni contact reveals extensive GaAs consumption. Much less consumption occurs in the Au/Ge/Pd contact. The absence of Au in the Ge/Pd contact leads to an extremely abrupt contact interface, with the Ge concentration dropping by four orders of magnitude within ∼100 Å of the interface. The Si/Pd contact is similar, with evidence of a complex compound formation within 200 Å of the interface. An ∼200 Å InGaAs region is in evidence at the In/Pd contact interface. The Si/Ni/Mg p-type ohmic contact profiles illustrate the progressive development of NiSi with the Mg layer serving as a diffusion barrier. The results are supplemented by transmission electron microscopy (TEM), and compared to various models of ohmic contact formation.
Ion-assisted deposition effects on the surface structure of a TiO2 thin film
Authors: Varnier F.
Published: July 2002

In this paper we present a comparison between the structure and roughness of two TiO2 thin films evaporated without and with ion bombardment, respectively. It is found that both their structure and their roughness are very different. Indeed, the film evaporated with ion bombardment exhibits a very smooth background with deep funnel shaped holes, while the other film surface proves to be both rough and rolling.
Atomic hydrogen chemisorption on the Si(111) 7×7 surface
Authors: Sakurai Toshio , Hasegawa Y. , Hashizume T. , Kamiya I. , Ide T. , Sumita I. , Pickering H. W. , Hyodo S.
Published: July 2002

Chemisorption of atomic hydrogen on the Si(111) 7×7 surface was investigated using scanning tunneling microscopy. Contrary to the recent report by Golovchenko’s group that the monohydride phase is not stable even at room temperature, resulting in the formation of the trihydride phase, our scanning tunneling microscopy (STM) experiment has shown that the monohydride phase is indeed the stable phase on the clean Si(111) 7×7 surface.
Products of pulsed laser induced thermal decomposition of triethylgallium and trimethylgallium adsorbed on GaAs(100)
Authors: Donnelly V. M.
Published: July 2002

Products of pulsed laser-induced decomposition of triethylgallium (TEGa) and trimethylgallium (TMGa) chemisorbed on GaAs(100) were determined and compared to those observed in thermal desorption. The desorbing products, C2H5, C2H4, and Ga(C2H5)x (x=2 and/or 3) for TEGa decomposition, and CH3 and Ga(CH3)x (x=2 and/or 3) for TMGa, are the same as those produced in thermal desorption. However, rapid substrate heating with the pulsed excimer laser causes large changes in the relative yields. With laser induced heating, Ga-alkyl desorption is almost completely suppressed in favor of further decomposition to yield hydrocarbon products and leave Ga on the surface, while in thermal desorption the Ga-alkyl is a major product. Furthermore, for laser-induced thermal decomposition of TEGa, C2H5 production is enhanced with respect to C2H4. These effects are ascribed to decomposition of chemisorbed GaR2(ads) (R=CH3, or C2H5), leading to formation of adsorbed GaR(ads) and desorption of R(g). This decomposition reaction is entropically favored over desorption of the Ga-alkyl, but has a higher activation energy. Consequently, decomposition is favored at the rapid heating rates, while desorption of GaRx dominates at slow heating rates. Competition between these desorption and decomposition reactions is likely important in the overall conversion of TEGa and TMGa to expitaxially grown, Ga-containing III–V compound semiconductor films. Arrhenius parameters are presented for the GaR2 decomposition reactions. These data should improve the accuracy of kinetic models for epitaxial film growth by chemical vapor deposition and molecular beam techniques.
Nucleation of diamond on silicon, SiAlON, and graphite substrates coated with an a-C:H layer
Authors: Dubray J. J. , Pantano C. G. , Meloncelli M. , Bertran E.
Published: July 2002

We investigated the influence of a hydrogenated disordered carbon (a-C:H) layer on the nucleation of diamond. Substrates c-Si〈100〉, SiAlON, and highly oriented pyrolytic graphite {0001} were used in this study. The substrate surfaces were characterized with Auger electron spectroscopy (AES) while diamond growth was followed with Raman spectroscopy and scanning electron microscopy (SEM). It was found that on silicon and SiAlON substrates the presence of the a-C:H layer enabled diamond to grow readily without any polishing treatment. Moreover, more continuous diamond films could be grown when the substrate was polished with diamond powder prior to the deposition of the a-C:H layer. This important result suggests that the nucleation of diamond occurs readily on disordered carbon surfaces, and that the formation of this type of layer is indeed one step in the diamond nucleation mechanism. Altogether, the data refute the argument that silicon defects play a direct role in the nucleation process. Auger spectra revealed that for short deposition times and untreated silicon surfaces, the deposited layer corresponds to an amorphous carbon layer. In these cases, the subsequent diamond nucleation was found to be limited. However, when the diamond nucleation density was found to be high; i.e., after lengthy deposits of a-C:H or after diamond polishing, the Auger spectra suggested diamondlike carbon layers.
The effects of substrate bias on plasma parameters in an electron cyclotron resonance plasma reactor
Authors: Caughman John B. O. , Holber William M.
Published: July 2002

The effect of substrate bias on plasma parameters has been studied for an electron cyclotron resonance plasma under typical materials processing conditions. Substrate conditions include floating with respect to the plasma, negative dc bias, or capacitively coupled rf bias. It has been found that the dc-bias can profoundly affect the electron density, the electron temperature, and the plasma potential, well into the bulk of the plasma. The rf bias is found to be generally less perturbative, though can still cause significant change in the plasma potential. Changing the rf bias frequency appears to alter the effects on the bulk plasma.
Coevaporation of Y, BaF2, and Cu utilizing a quadrupole mass spectrometer as a rate measuring probe
Authors: Hudner J. , Östling M. , Ohlsén H. , Stolt L.
Published: July 2002

An ultrahigh vacuum coevaporator equipped with three sources for preparation of Y–BaF2 –Cu–O thin films is described. Evaporation rates of Y, BaF2, and Cu were controlled using a quadrupole mass spectrometer operating in a multiplexed mode. To evaluate the method depositions have been performed using different source configurations and evaporation rates. Utilizing Rutherford backscattering spectrometry absolute values of the actual evaporation rates were determined. It was observed that the mass-spectrometer sensitivity is highest for Y, followed by BaF2 (BaF+ is the measured ion) and Cu. A partial pressure of oxygen during evaporation of Y, BaF2, and Cu affected mainly the rate of Y. It is shown that the mass spectrometer can be utilized to precisely control the film composition.
Evaluation of new ozone generator designed for oxide film formation by molecular beam epitaxy method
Authors: Ichimura S. , Hosokawa S. , Nonaka H. , Arai K.
Published: July 2002

The quality of ozone vapor produced with a new ozone generator was evaluated. The ozone vapor was produced by evaporation of liquid ozone after accumulating it in a ozone vessel at various temperatures between 75 and 95 K. Mass analysis of the ozone vapor revealed that the purity of ozone in the vapor depended on both the ozone vessel temperature during liquefaction and that during evaporation. The purity was ∼70% when liquid ozone accumulation temperatures higher than 90 K were used. The activity of the ozone vapor was investigated by oxidation of a Cu foil under low pressure condition. The formation of a CuO layer by exposure to the ozone vapor (pressure: ∼5×10−4 Pa) at 300 °C was confirmed through x-ray photoelectron spectroscopy analysis.
Surface photovoltage effects in photoemission from metal/GaP(110) interfaces: Temperature-dependent Fermi level movement
Authors: Alonso M. , Cimino R. , Horn K.
Published: July 2002

In recent experiments of metal deposition onto cleaved GaP(110) surfaces we have shown that light sources used in photoelectron spectroscopy may induce a surface photovoltage (SPV), which causes a substantial deviation from the ground state potential distribution, and may induce errors in the determination of band bending by photoemission. Here we analyze the temperature-dependent movement of the surface Fermi level in n- and p-type GaP(110) surfaces as a function of indium and silver deposition, taking into account the presence of the SPV. It is found that changes in the substrate temperature not only modify the adlayer morphology and metallicity, but also the surface electron-hole recombination rate. We observe that the temperature-dependent shift of the semiconductor core levels is always accompanied by a similar shift of the metal core level and Fermi edge, suggesting that the reversible temperature-dependent band bending recently reported for metal/III–V semiconductor interfaces is related to the SPV, and does not represent a ground state property of the interfacial electronic structure. Implications of these results on current models concerning Schottky barrier formation are discussed.
Formation and Schottky barrier height of Au contacts to CuInSe2
Authors: Nelson Art J. , Gebhard Steven , Kazmerski L. L. , Colavita Elio , Engelhardt Mike , Höchst Hartmut
Published: July 2002

Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Au/CuInSe2 interface. Au overlayers were deposited in steps on single-crystal p and n-type CuInSe2 at ambient temperature. Reflection high-energy electron diffraction analysis before and during growth of the Au overlayers indicated that the Au overlayer was amorphous. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the Au/CuInSe2 Schottky barrier height.
Characterization of ion beam-induced surface modification of diamond films by real time spectroscopic ellipsometry
Authors: Cong Yue , Collins R. W. , Messier R. , Vedam K. , Epps Glenn F. , Windischmann H.
Published: July 2002

Real time spectroscopic ellipsometry from 1.5 to 4.0 eV has been applied to monitor surfaces of optical quality diamond thin films during exposure to low energy Ar and H ion beams, and atomic H. Monolayer-level sensitivity to the conversion of diamond to optically absorbing sp2 bonded carbon upon ion impact is demonstrated. For Ar ions, a beam voltage of 50 V is found to be sufficient to convert the surface to the equivalent of a single monolayer of sp2 bonded carbon, whereas the topmost 12–16 Å is converted at the threshold for sputter etching, between 100 and 150 V. Atomic H and low energy H ion treatments (≤50 V) are found to eliminate optically absorbing defects within 15 Å of the surface. The overall results provide optimism that real time spectroscopic ellipsometry will be a highly sensitive real time probe of diamond surface and bulk microstructure in the reactive environments of enhanced chemical vapor deposition.
Surface and electron microscopic analysis of Ni–Cr alloy films deposited from a single source
Authors: Sethuraman A. R. , Reucroft P. J. , Okazaki K. , De Angelis R. J.
Published: July 2002

Three compositions of Ni–Cr (75% Ni–25% Cr, 50% Ni–50% Cr and 25% Ni–75% Cr by weight) alloy evaporation sources were synthesized using electrodischarge compaction.1 Thin films of Ni–Cr of about 700-Å thick were deposited on silicon substrates for surface studies and on carbon coated Formvar grids for structural observations. The surface and interface properties of the films were studied by depth profiling using Auger electron spectroscopy (AES) and the structural properties were studied by transmission electron microscopy (TEM). TEM results indicated that about 25% Cr in the alloy films was enough to stabilize a majority Cr phase and the structure was found to be that of a body-centered-cubic alloy.
Nucleation and growth of silicon on SiO2 during SiH4 low pressure chemical vapor deposition as studied by hydrogen desorption titration
Authors: Liehr M. , Dana S. S. , Anderle M.
Published: July 2002

We have developed a new approach to characterize the initial stages of nucleation and early growth of Si on SiO2 from SiH4 at low pressures. In a rapid thermal chemical vapor deposition reactor a sequence of alternating growth and hydrogen thermal desorption cycles using an in situ mass spectrometer is carried out. Desorption of hydrogen (a reaction product) is used to titrate the area of exposed Si surface on the SiO2 surface after each growth step. A sensitivity of better than 10−3 monolayers (ML) is demonstrated. Nucleation and growth of Si islands is seen upon SiH4 exposure under chemical vapor deposition conditions (500–700 °C). Once nucleated, the islands grow in size at rates consistent with those of Si epitaxial growth until they merge to form a polycrystalline film.
Evaluation of surface analysis methods for characterization of trace metal surface contaminants found in silicon integrated circuit manufacturing
Authors: Diebold Alain C. , Maillot P. , Gordon M. , Baylis J. , Chacon J. , Witowski R. , Arlinghaus H. F. , Knapp J. A. , Doyle B. L.
Published: July 2002

We report a preliminary investigation of surface analytical methods used to evaluate trace metal contaminants on silicon wafer surfaces. The methods discussed include sputter induced postionization methods, backscattering spectrometry, total reflection x-ray fluorescence, and a sample preparation method known as vapor phase decomposition. In order to initiate the evaluation, a series of silicon wafers was dosed with transition metal contaminants Cu and Fe and then analyzed with total reflection x-ray fluorescence, sputter induced resonant ionization spectroscopy, and heavy ion backscattering spectroscopy. One wafer with low concentrations of Fe was analyzed by time of flight secondary ion mass spectrometry. As a result of this study, we are pursuing improved capability in several areas including standards. Heavy ion backscattering spectrometry is suggested as a means of verifying surface dosed silicon wafer standard.
Reflection high-energy electron diffraction intensity oscillations and surface reconstructions measured during epitaxial growth of Si(001) from Si2H6 molecular beams
Authors: Mokler S. M. , Liu W. K. , Ohtani N. , Joyce B. A.
Published: July 2002

The growth of Si(001) from a gas source molecular-beam epitaxy system using disilane (Si2H6) was investigated using reflection high-energy electron diffraction (RHEED). Surface reconstructions which occurred during growth were studied as a function of both substrate temperature and surface coverage. Growth below 600 °C was found to be initiated by the formation of three-dimensional (3D) islands. Near 645 °C, (2×2) and c(4×4) reconstructions occurred on the growing Si(001) surface. At higher temperatures, above 680 °C, growth was found to proceed two dimensionally. The Si(001) surface was found to have undergone a series of reconstructions which have been attributed to the number of hydrogen adatoms and Si dimers covering the surface. RHEED intensity oscillations have been used to monitor Si(001) during growth. Oscillations are easily obtained on well prepared surfaces on which a buffer layer has been grown. Oscillations of the specular beam in both the [010] and [110] azimuths have been measured as a function of temperature and disilane flow rate. Strong and damped oscillations are observed between 610 and 680 °C in the two-dimensional growth regime. At higher temperatures growth by step propagation dominated, while at lower temperatures growth became three dimensional (3D) and consequently oscillations were weak or absent. Oscillations of the fractional order and specular beams in the [110] azimuths indicate that growth occurs in a monolayer rather than a bilayer fashion, and the alternating intensity of sequential oscillations in the specularly reflected beam in the [110] azimuth may be indicative of the relative step density in the two orthogonal directions. Growth rates, as determined from the oscillations, are found to be independent of incident beam flux at substrate temperatures below 600 °C. Above this temperature the growth rate increases proportionally to the incident flux. An Ahrrenius plot indicates an activation energy (EA) of 40.7 kcal/mol in the low temperature regime (T<600 °C) and an apparent EA dependence on disilane flux in the high temperature regime.
Optical properties of ion assisted deposited zirconia thin films
Authors: Krishna M. Ghanashyam , Rao K. Narasimha , Mohan S.
Published: July 2002

The nature of the dependence of refractive index, extinction coefficient, and packing density of zirconia films prepared by ion assisted deposition on the energy and current density of ions has been investigated. A broad beam Kaufman ion source has been used to generate oxygen ions in the energy range 100–700 eV and current densities up to 220 μA/cm2. It has been found that the refractive index increases steadily up to an energy of 500 eV beyond which there is a nominal decrease. The highest index obtained was 2.21 at an energy of 500 eV and a current density of 220 μA/cm2. Similarly, with an increase in the current density the refractive index increases initially and seems to saturate beyond a certain critical value dependent on the ion energy. The extinction coefficient was low up to an energy of 300 eV showing a marked increase thereafter. The extinction coefficient was also found to increase at high ion current densities and energies. A critical ion energy and current density beyond which the refractive index as well as the extinction coefficient of these films start deteriorating has been observed.
Effects of target presputtering on stoichiometry of sputtered Bi–Sr–Ca–Cu–O thin films
Authors: Yang YiFeng , Lee Ji Ung , Nordman James E.
Published: July 2002

We have studied the target presputtering effects on the stoichiometry of Bi–Sr–Ca–Cu–O (BSCCO) thin films prepared from a single composite target using rf magnetron sputtering in a vacuum system with a pressure of 10−6 Torr. A strong dependence of film composition on the target presputtering time has been found under pure argon discharge. A rather long time (∼20 h) is needed to bring the target to a steady state condition. The oxygen out-diffusion under the aid of energetic particle bombardment is believed to be the cause of this effect, a physical process similar to that observed in the Y–Ba–Cu–O system. It has been further demonstrated that introduction of oxygen into the sputtering chamber can effectively prevent this process from taking place and therefore preserve the BSCCO target surface in its initial state.
High reflectivity dielectric mirror deposition by reactive magnetron sputtering
Authors: Scherer A. , Walther M. , Schiavone L. M. , Van der Gaag B. P. , Beebe E. D.
Published: July 2002

We use room temperature reactive sputter deposition from a silicon target to deposit Si, Si3N4, and SiO2 layers. The resulting amorphous layers are grown to form highly reflecting dielectric mirrors and used for coating end facets of layers. Among the advantages of our computer controlled sputter deposition process are the reproducibly excellent optical quality, good adhesion properties together with high chemical and thermal stability of the deposited films. We use Si/SiO2 mirrors for broadband infrared distributed Bragg reflectors and Si3N4/SiO2 multilayers in the visible wavelength range. The high (≳99%) reflectivities which are obtained from these mirrors make them suitable for use in vertical-cavity surface emitting and low-threshold edge-emitting lasers.
Highly reflective x-ray mirror
Authors: Itabashi Sei-ichi , Okada Ikuo , Kaneko Takashi , Matsuo Seitaro , Yoshihara Hideo
Published: July 2002

A highly reflective x-ray mirror is needed for creating an efficient synchrotron-radiation lithography beamline. Three kinds of deposition methods are therefore compared: electron-cyclotron-resonance (ECR) sputtering, ion-beam sputtering, and conventional vacuum evaporation. These methods differ with respect to the particle energy irradiating a surface: Ions in ECR plasma have energies of 10–100 eV, ion-beam-sputtered particles have energies of 1–10 eV, and vacuum-evaporated particles have energies of about 0.1 eV. The surface roughness and morphology of platinum films are evaluated here by x-ray reflectivity, scanning tunneling micrography, and scanning electron micrography. The three kinds of films differ in surface roughness and morphology. The ECR-sputtered Pt film has the highest x-ray reflectivity and the lowest surface roughness. The minimum surface roughness of a 10-nm-thick ECR-sputtered film is 0.3 nm. Because this film is thick enough to reflect x rays, ECR sputtering seems to be the best method for preparing highly reflective x-ray mirrors.
Cyclic annealing-induced microstructural and crystallographic changes in crystalline yttria films on silica
Authors: Mukherjee S. N. , Aita C. R.
Published: July 2002

A cyclic air-annealing study of crystalline yttria films sputter deposited on fused silica is reported here. The results show major microstructural instability after a short time (0.5 h) at temperature (700 °C), involving localized stress relief as the film undergoes biaxial compression→tension during a heating→cooling cycle. Long-term cyclic annealing causes delamination by interfacial bubble formation and explosion. Accompanying crystallographic changes are discussed. The results are compared with those for amorphous yttria-on-silica, in which stress relief is entirely by hillock formation, growth, and coalescence.
Temperature distribution in an ideal azimuthally symmetric chemical-vapor-deposition reactor
Authors: Kotecki David E. , Conti Richard A.
Published: July 2002

The temperature distribution in an azimuthally symmetric chemical-vapor-deposition reactor is calculated at two pressure regimes. Taken into account is the influence of a silicon wafer situated above a uniformly heated susceptor. In the low-pressure regime, where the mean free path in the gas phase is much greater than the separation between the wafer and susceptor, the wafer is heated solely by radiation. The temperature at the wafer surface can be ∼20% lower than the susceptor temperature and the temperature drop is nearly independent of the thermal conductivity of the surrounding gas. In the high-pressure regime, where continuum flow exists between the susceptor and the wafer, the later is heated by conduction, convection, and radiation. The temperature at the wafer surface can be ∼10% lower than that of the susceptor and the temperature drop is strongly influenced by the distance separating the wafer and the susceptor, and by the thermal conductivity of the gas. In both pressure regimes, nonuniform temperature profiles develop at the wafer surface and in the gas phase directly above the wafer. In the reactor geometry studied, a nonuniform susceptor temperature profile would be required to produce uniform wafer and gas-phase temperature profiles.
In situ characterization of sputtered thin films using a normal incidence laser reflectometer
Authors: Babić Dubravko I. , Reynolds Thomas E. , Hu Evelyn L. , Bowers John E.
Published: July 2002

We will demonstrate the implementation and the use of a normal incidence semiconductor laser reflectometer as an in situ monitoring tool in a computer automated system for reactive sputter deposition of Si/SiOx/SiNx dielectric films. An anode with a viewing hole that was designed specifically for this purpose enables the introduction of both the sputtering gases and the collimated laser beam into the vacuum chamber normal to the processed wafer surface. We will discuss the reflectometer design considerations and the automated data acquisition. We will also demonstrate the use of a normal incidence reflectivity measurement system for in situ determination of the optical deposition rate and material properties such as the refractive index and the absorption loss.
Properties of plasma assisted chemical vapor deposited coatings of titanium boride on Ti–6Al–4V alloy substrates
Authors: Otter F. A. , Amisola G. B. , Roman W. C. , Hay S. O.
Published: July 2002

Coatings prepared in a radio-frequency-plasma (plasma assisted chemical vapor deposition) reactor employing in situ laser diagnostics have been tested and characterized. Detailed characterization studies are important to relate gas phase laser diagnostic studies and concurrent heterogeneous modeling efforts to coating characteristics. Establishing how deposition conditions are correlated with coating properties is expected to provide needed methodology for scale up of applications in the hard face protective coating area. After a brief discussion of preparation conditions and mechanical test results, we present results of chemical and physical measurements on these coatings. Measurement techniques include x-ray diffraction, Dektak surface roughness, scanning tunneling microscopy, scanning electron microscopy, and SEI, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. The coatings (∼20 μm thick) are very hard (40 GPa at depths over 100 nm), adherent (60 N on scratch test), and sand erosion resistant (≳40× as durable as Ti-6Al-4V). They are highly oriented with the c axis (hexagonal-close-packed) normal to the coating surface, rough (∼1 μm), and off-stoichiometry (TiB2.2).
Structural and geometrical features of copper seed cones observed by high-resolution electron microscopy
Authors: Mori Y. , Fujimoto Y. , Okuyama F.
Published: July 2002

Structural and geometrical properties of cones developed on Cu surfaces bombarded with obliquely incident Ar+ ions while simultaneously supplying ‘‘seeds’’ by sputtering were determined in atomic detail, by means of high-resolution electron microscopy. The seed materials employed were Mo, W, Ta, Ti, and Pt, and sputtered seed atoms were found to coat the upper cone slopes which received high seed fluxes, independently of seed species. The seed films thus formed were monocrystalline for Mo, W, and Pt, and amorphous or semiamorphous for Ta and Ti. Geometrically, the cones induced by Mo, W, Ta, and Ti were conelike, but those formed on the Pt-seeded surfaces were tentlike rather than conelike. For the conelike geometries, the tip of seed layer was grown so as to shield the substrate part of the cone from the ion beam. Perhaps, seed atoms must be more resistant to sputtering than target atoms, for seed cones to be conelike.
Correlation of the interfacial structure and electrical properties of epitaxial silicides on Si
Authors: Sullivan J. P. , Tung R. T. , Schrey F. , Graham W. R.
Published: July 2002

The Schottky barrier height (SBH) measured at epitaxial NiSi2 contacts is shown to be strongly influenced by the local interfacial structure. Diodes with guard rings, which eliminate the edge leakage current which has hampered some previous studies, were prepared by molecular-beam epitaxy of NiSi2 films on a wide range of n- and p-type doped Si substrates. Schottky diodes processed with high quality NiSi2 films on Si(111) are shown to exhibit highly ideal electrical properties. Structural inhomogeneity at the NiSi2/Si(100) interface is shown to lead to electrical properties which are consistent with the existence of spatial inhomogeneity in the SBH. Numerical simulations of the electron transport across the inhomogeneous diodes, based on a spatial variation of the interfacial SBH consistent with the observed structural inhomogeneity in the films, are shown to accurately reproduce the trends in the electrical behavior of the inhomogeneous diodes. The necessity to understand the interfacial atomic structure at metal/semiconductor contacts in order to understand the formation mechanism of the Schottky barrier is stressed by these results.
Micrometer patterning of phthalocyanine derivatives by selective chemical vapor deposition method
Authors: Sekiguchi A. , Pasztor K. , Shimo N. , Masuhara H.
Published: July 2002

Selective chemical vapor deposition was achieved to produce copper phthalocyanine thin films on the copper microelectrodes on insulating and optically transparent materials. By thermally annealing the fabricated films at 500 °C under vacuum, their quality was greatly improved and the conductivity of the modified copper microelectrodes became high.
Nucleation and growth of DyBa2Cu3O7−x thin films on SrTiO3 substrates studied by transmission electron microscopy and atomic force microscopy
Authors: Agrawal V. , Chandrasekhar N. , Zhang Y. J. , Achutharaman V. S. , Mecartney M. L. , Goldman A. M.
Published: July 2002

The microstructure of superconducting films influence their properties, requiring optimization of processing conditions. The early stages of nucleation and growth determine the final microstructure of the film. We report our studies of the initial stages of epitaxial growth of DyBa2Cu3O7−x films on SrTiO3 substrates by transmission electron microscopy (TEM), atomic force microscopy (AFM), and reflection high energy electron diffraction (RHEED). Prethinned, electron transparent, reconstructed (100) and (110) SrTiO3 substrates were used to deposit 40-, 100-, and 1000-Å-thick DBCO films by ozone-assisted molecular beam epitaxy (MBE). The reconstructed substrates have a stepped surface and the film nucleates preferentially at the steps giving rise to an interconnected network of islands. The growth mechanism appears to be nucleation at the step edges and propagation of these steps. In situ reflection high energy electron diffraction yielded identical conclusions. Islands saturate at a certain size and further coverage merely increases the number of islands. This has significance in the application of ultrathin DyBa2Cu3O7−x films to devices and their use as a model systems to study superconductivity. Factors other than the substrate temperature, such as substrate surface morphology are found to influence the epitaxial relationship.
An apparatus for ion-beam sputtering and its application to high-resolution radiotracer depth profiling of diffusion samples
Authors: Faupel F. , Hüppe P. W. , Rätzke K. , Willecke R. , Hehenkamp Th.
Published: July 2002

An apparatus for direct current ion beam sputtering is described which incorporates some new features, specifically with respect to target and plasma current control. In conjunction with a radiotracer technique it is demonstrated how resolution and sensitivity of depth profiling can be substantially enhanced by reduction of the ion energy and correction for after effects in sputtering. Investigations of metal diffusion in polymers and isotope effect measurements in metallic glasses are presented as examples.
Interfacial band alignments for LaF3, NdF3, and TmF3 heterojunctions on Si(111)
Authors: Colbow K. M. , Gao Y. , Tiedje T. , Dahn J. R. , Reimers J. N. , Cramm S.
Published: July 2002

Thin films of the rare-earth trifluorides (LaF3, NdF3, TmF3) grown on clean Si(111) surfaces have been studied by photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. By resonant excitation of the giant 4d–4ftransition in NdF3 and TmF3, we are able to enhance the photoemission signal from the partially occupied 4f orbitals and distinguish it from the photoemission signal of the overlapping F 2p valence band. We show that the valence-band offset is the same for heterojunctions of the three different fluorides on Si(111), and determine the energies of the cation 4f orbitals relative to the F 2p valence band.
Study on radio frequency reactive sputtering deposition of silicon nitride thin films
Authors: Stedile F. C. , Baumvol I. J. R. , Schreiner W. H. , Freire F. L.
Published: July 2002

A rf magnetron sputtering apparatus operating at constant gas pressure was used to deposit silicon nitride thin films in an Ar–N2 plasma. The nitrogen partial pressure, incident rf power, and the deposition time were varied to obtain various sets of films. In analyzing the stoichiometry and thickness of the silicon nitride films by Rutherford backscattering spectroscopy, several correlations among deposition parameters and film characteristics could be found. The results can be discussed by adapting a reactive sputtering theoretical model to the present conditions. An alternative method to grow films with the same stoichiometry but under different deposition rates was tested.
X-ray diffraction characterization of superlattices grown on offcut (100) substrates
Authors: Maigne P.
Published: July 2002

An x-ray diffraction procedure is proposed to fully characterize the structural parameters of superlattices and multiple quantum wells grown on misoriented substrates. The procedure requires the acquisition of x-ray rocking curves, as a function of the azimuthal angle φ, from which the offcut angle ε and the tilt angle β between the (100) planes of the substrate and the superlattice can be measured. The direction of the tilt can also be measured and it is shown on a sample comprising a ten period InGaAs/GaAs superlattice, that this direction is not necessarily coplanar with the surface normal and the GaAs (100) direction. The proposed procedure also includes the fitting of the experimental data using a simulation program which takes into account the values of φ, ε, and β. The simulation program used the kinematical approximation and is based on a simple approach which reproduces the independence of the satellite peak spacing with the azimuth, as observed in the measurements.
Effects of surfaces on H-atom concentration in pulsed and continuous discharges
Authors: Tserepi Angeliki D. , Dunlop James R. , Preppernau Bryan L. , Miller Terry A.
Published: July 2002

We report on the effect of Si and GaAs substrate materials on the hydrogen atom ground-state concentration profiles in 10 MHz pulsed and continuous rf discharges. We measure absolute hydrogen atom concentrations in the discharge via two-photon absorption laser-induced fluorescence. The spatial profiles of the H atoms in an unloaded plasma reactor show a concentration on the order of 1014 atoms/cm3 at the center of the discharge, a concentration relatively constant until it sharply decreases at a 3–4 mm distance away from the electrode surfaces. However, when the discharge is loaded with semiconducting materials, the H-atom concentration drastically increases at the region adjacent to the semiconducting surfaces. The evolution of these profiles obtained in a pulsed discharge suggests that the H atoms are produced in localized regions in the discharge, and they diffuse towards the center and the confining surfaces. We discuss the validity of a diffusion model which treats the metallic surfaces as sinks, and the Si and GaAs surfaces as nearly perfect reflectors.
Cryogenic electron cyclotron resonance plasma etching
Authors: Whang Ki Woong , Lee Seok Hyun , Lee Ho Jun
Published: July 2002

A cryogenic electron cyclotron resonance (ECR) plasma etching system has been built to study wafer temperature in the Si etching characteristics. The wafer temperature was controlled from −150 to +30 °C during etching using the liquid nitrogen cooled helium gas. Although Si was etched isotropically in SF6 plasmas at room temperatures, we found that it is possible to suppress the etch undercut in Si by reducing a substrate temperature without sidewall passivation. In addition, the selectivity of silicon to photoresist was improved considerably at a low wafer temperature. ECR etching generates less damage in the gate oxide than reactive ion etching does under comparable etching conditions.
Two-dimensional model of glow discharges for a cylindrical geometry
Authors: Hashiguchi Seishiro
Published: July 2002

A computer simulation of a dc glow discharge is presented. The simulation consists of a two-dimensional continuum model for electron and ion transport using the local field approximation. The continuity equations of electron and ion are coupled with Poisson’s equation for a given set of boundary conditions. Potential values on insulator are determined by taking surface charges on it into account. Numerical calculations were made for 1 Torr helium glow discharges in a cylindrical discharge vessel with an electrode on each end. The current density Ic ranged from 1 to 40 μ A/cm2. The voltage–current curve has a minimum voltage at about Ic = 4μA/cm2. At higher values of Ic, a typical character of glow discharge was realized; peak ion density in front of the cathode and charge-neutrality region in front of the anode.
Characterization of biased electron cyclotron resonance deposited oxides
Authors: Bulat E. S. , Ditmer G. , Herrick C. , Hankin S.
Published: July 2002

An extensive study characterizing the properties of silicon oxide films deposited using biased electron cyclotron resonance (ECR) plasmas was performed. The ECR system provided microwave plasma excitation at 2.45 GHz, at power levels from 200 to 1000 W. Confinement of the resonant plasma was achieved using two independent current-controlled electromagnets. The deposition gases were O2, N2O, and dilute silane in Ar; process flow rate, pressure, and microwave power were held constant. Radio frequency power was applied to the substrate electrode to attain a bias that was varied from 0 to 300 V to affect film characteristics. The uniformity, refractive index, stress, and dry and wet etch rates of ECR oxides were evaluated and compared with thermal and low-pressure chemical vapor deposition oxides. In addition, infrared spectroscopy was performed to characterize ECR oxide stoichiometry. The dependence of the Si–O and O–H content of these films will be described as a function of bias voltage applied to the substrate electrode.
Scanning tunneling microscope-based nanostructure fabrication system*
Authors: Schneir J. , Dagata J. A. , Harary H. H.
Published: July 2002

We have designed a novel scanning tunneling microscope (STM) and control electronics system to investigate STM-based nanostructure fabrication on semiconductor surfaces. Several elements of our design are unique to this application. The STM, which resides in a vacuum chamber, can be positioned anywhere on a 1 cm×1 cm sample. This is accomplished by using three piezoelectric motors (Burleigh Inchworms) and locating the tip position with a long working distance optical microscope (Questar). One piezoelectric motor is used for the coarse Z approach while the other two adjust the X,Y tip position. The tip is attached to a tube-type piezoelectric scanner. The piezo tube’s x–y scan range is 12 μm×12 μm. The tube’s mechanical and electrical response are linear to 6 kHz and allow rapid scanning. Both tip and sample are attached to the microscope magnetically to facilitate rapid self-aligned exchange under vacuum. A computer controlled pattern generation system allows arbitrary patterns to be drawn on the sample. The critical electromechanical issues involved in the construction and operation of such a system are discussed in detail.
First results of microspectroscopy from a scanning photoemission microscope with a submicron probe size
Authors: Ray-Chaudhuri A. K. , Ng W. , Liang S. , Singh S. , Welnak J. T. , Wallace J. P. , Capasso C. , Cerrina F. , Margaritondo G. , Underwood J. H. , Kortright J. B. , Perera R. C. C.
Published: July 2002

Utilizing a Mo–Si multilayer coated Schwarzschild objective to focus 95 eV photons, we have recently demonstrated better than 0.1 μm resolution as a scanning x-ray transmission microscope. Operating as a scanning photoemission microscope with submicron resolution, we have demonstrated its chemical mapping capabilities by studying a patterned Al/AlOx test structure. In addition, we have also studied the cleaved GaAs(110) surface and have identified lateral variations in the surface band bending on the scale of 100 meV. In both experiments, core level microspectroscopy was performed at selected points on the sample to elucidate the image contrast mechanisms.
Promoted oxidation of aluminum thin films using an alkali metal catalyst
Authors: Huttel Y. , Bourdié E. , Soukiassian P. , Mangat P. S. , Hurych Z.
Published: July 2002

We investigate the effect of sodium overlayers on the oxidation of aluminum thin films by means of core level and valence band photoemission spectroscopy using synchrotron radiation. The presence of Na enhances the oxidation rate of the aluminum by nearly 4 orders of magnitude with formation, at room temperature, of alumina likely as α-Al2O3. The sodium catalyst is removed by thermal desorption at temperatures below 300 °C leading to the formation of an aluminum oxide having a larger binding energy than stoichiometric alumina. It indicates the formation at the surface of an aluminum oxide having higher oxidation states as Al2O3+x. Unlike catalytic oxidation of elemental semiconductors such as silicon, formation of Na related oxides are shown to play an important role in the alkali metal promoted aluminum oxidation. Interestingly, Na appears a more efficient catalyst for Al thin film than on single crystal surface. The micromechanisms of promotion are found to be significantly different from that of alkali metal promoted oxidation of semiconductor surfaces.
Damage introduction in GaAs/AlGaAs and InGaAs/InP heterojunction bipolar transistor structures during electron cyclotron resonance plasma processing
Authors: Ren F. , Fullowan T. R. , Pearton S. J. , Lothian J. R. , Esagui R. , Abernathy C. R. , Hobson W. S.
Published: July 2002

Dry etching is used for a number of processing steps in the fabrication of small geometry (∼2×5 μm2 emitter dimension), high speed (fT, fmax≥50 GHz) heterojunction bipolar transistors, including emitter, base, and collector mesa definition, sidewall etch-back, and trilevel resist patterning. These steps involve the use of numerous plasma chemistries (CCl2F2 or BCl3 for GaAs/AlGaAs, CH4/H2 for InGaAs/InP, SF6 for dielectric sidewalls, and O2 for resist). We have conducted a systematic study of the threshold dc self-biases for these discharges below which there is no significant damage introduction in the semiconductor. In a low pressure hybrid electron cyclotron resonance-radio frequency reactor, these biases are a function of the doping type, doping level and the thickness of the exposed III–V layers. Changes in the sheet resistance and diode ideality factor of p–n junctions in each material system were examined as a function of the time (1–20 min), plasma pressure (1–20 mTorr), and additional rf-induced dc bias to obtain the optimum dry etch conditions. In our structures, dc biases of ≤−100 V appear to yield damage free etching. At higher biases, the damage depth dependence on bias was examined using the Seaward and Moll [J. Vac. Sci. Technol. B 9, 1445 (1991)] model and also by direct C–V profiling.