bluuebunny/crossref_metadata_2025 huggingface dataset:
High rate reactive magnetron sputtered tungsten carbide films
Authors: Srivastava P. K. , Vankar V. D. , Chopra K. L.
Published: July 2002

Tungsten carbide films have been deposited on stainless steel substrates held between 300 to 500 °C in a planar rf magnetron sputtering system at rates as high as that of pure tungsten (825 A°/min). The effect of substrate temperature on formation of WCx films has been investigated. A mixture of hexagonal WC, A-15 W3C and carbon in graphitic and diamond form have been observed by AES and XRD techniques. The microhardness of these films has been found to be as high as 2365 kgf/mm2. The adhesion of these films as measured from indentation crack patterns has been found to depend on substrate temperature as well as on the amount of dispersed carbon in the film.
As+ implantation and transient annealing of MoSi2 thin films
Authors: Agamy S. A. , Ho V. Q. , Naguib H. M.
Published: July 2002

The effect of 100 keV arsenic implantation on the structural, compositional, and electrical properties of sputtered and annealed MoSi2 films is investigated. Before implantation, the silicide films had a tetragonal structure with a sheet resistance of approximately 2.2 Ω/⧠ for a nominal film thickness of 0.3 μm. As+ implantation increased the sheet resistance by approximately 140% of its initial value at a dose of 5×1016/cm2. Hexagonal MoSi2 phase was formed at implantation doses ≥5×1015/cm2. Rapid lamp annealing at 900 °C for 10 s removed the hexagonal phase but was not enough to restore the low sheet resistance of the unimplanted wafers. Transient annealing at 1100 °C for 10 s was sufficient to regain the low sheet resistance for all films (∼2.2 Ω/⧠). A thermal spike model was successfully applied to explain the absence of an amorphous phase and the formation of a low temperature hexagonal structure in high dose implantation films. In addition, the recorded RBS spectra showed pronounced low-energy tails which were independent of the implantation conditions. The origin of these tails was attributed to the anomalous surface morphology of the silicide films deposited on oxide layers.
Modulation doping in Ge(x)Si(1−x)/Si strained layer heterostructures: Effects of alloy layer thickness, doping setback, and cladding layer dopant concentration
Authors: People R. , Bean J. C. , Lang D. V.
Published: July 2002

Selectively doped GexSi1−x/Si strained layer heterostructures have been grown in a single quantum well configuration on 〈001〉-Si substrate using molecular beam epitaxy. The modulation doping effect has been observed in p-type structures only; although both n- and p-type double heterostructures were grown. We have investigated the effects of: (i) alloy layer thickness (well width), (ii) doping setback, and (iii) cladding layer dopant concentration, on the hole mobilities. At present, optimum structures show peak hole mobilities in excess of 3300 cm2V−1s−1 at 4.2 K, sheet charge densities of 3.0–14×1011 cm−2, and hole effective mass m*h =0.32±0.03 m0. It is found that the low temperature (T∼10 K) hole mobility, in structure having x=0.2 is relatively insensitive to alloy layer (well) thickness in the range 100 Å≲Lw≲Lc; where Lc is the critical thickness marking the transition from strained layer to relaxed, misfit accommodated, alloy growth. For Lw>Lc, misfit dislocation scattering dramatically decreases μh at T≲100 K; whereas for Lw≲100 Å the hole mobility is uniformly lowered over the entire range of measurement temperatures. Doping setback and cladding layer dopant concentration affect the mobility via changes in sheet charge density, in a manner consistent with theoretical expectations. The absence of the modulation doping effect in n-type heterostructure is taken as an indication that ΔEv≫ΔEc.
Reaction at a refractory metal/semiconductor interface: V/GaAs(110)
Authors: Grioni M. , Joyce J. J. , Weaver J. H.
Published: July 2002

Synchrotron radiation photoemission spectroscopy has been used to study the formation of the reactive V/GaAs(110) interface. Valence-band and core-level results indicate that metal deposition produces an extended intermixed phase involving the formation of both V–Ga and V–As bonds. In this reacted region the Ga 3d core line exhibits a continuous shift to lower binding energy (total shift 1.55 eV over band bending) indicative of a variable chemical environment, while analysis of the As 3d line shape suggests that As is present in two well-defined chemical states. Core-level intensity profiles show preferential outdiffusion of arsenic, with As present at ∼6% of the original level with coverages of 110 Å. Comparison to previous results for Cr/GaAs(110) shows similar Ga and As attenuation profiles.
Anthracene and polyethylene thin film depositions by ionized cluster beam
Authors: Usui H. , Yamada I. , Takagi T.
Published: July 2002

Anthracene and polyethylene thin films were deposited by ionized cluster beam (ICB). Films deposited at optimum ion acceleration voltage showed strong preferential crystal orientation. The dependencies of crystal orientation and film grain size on deposition conditions were investigated. The photoluminescent and electroluminescent properties of anthracene films deposited by ICB were superior to those properties of similar films produced by vacuum deposition. In the case of polyethylene, it was found that in films produced by ICB, the molecules contain fewer side chains than in the source material. The lattice parameter in ICB polyethylene films was close to that of the single crystal polyethylene material. Strength of film–substrate adhesion was improved by increasing ion acceleration voltage.
A study of chemical bonding in suboxides of silicon using Auger electron spectroscopy
Authors: Chao S. S. , Tyler J. E. , Takagi Y. , Pai P. G. , Lucovsky G. , Lin S. Y. , Wong C. K. , Mantini M. J.
Published: July 2002

We have studied the chemical bonding in thin films of SiOx (x<2) by Auger electron spectroscopy (AES). We have compared the AES Si LVV spectra of suboxides of silicon with the AES Si LVV spectrum of stoichiometric SiO2 and have observed that the spectra of the suboxides are characterized by the emergence of a feature associated with Si–Si bonds that are present in the suboxides but not in stoichiometric SiO2. We have taken care to distinguish between spectral features that are associated with departures from SiO2 bulk stoichiometry, and features that are generated by ion and electron beam induced surface damage. Ion and electron beam induced damage produces changes in the surface composition that also generates AES spectral features associated with Si–Si bonds. We have based our interpretation of the additional AES spectral feature in the silicon suboxides on an empirical tight-binding model calculation for the electronic structure. This calculation shows that Si–Si bonding states in the suboxides appear near the middle of the energy gap of stoichiometric SiO2. The position of the new spectral feature in the suboxides is in agreement with the predictions of the model calculation.
Dependence of the electrical properties of Zn contacts to GaAs on the structural properties of the Zn–GaAs interface
Authors: Kulkarni A. K.
Published: July 2002

Ohmic contacts to p-type GaAs are extremely important in the fabrication of heterojunction lasers, integrated optical devices, and solar cells. The importance of the metallurgical properties of the Zn–GaAs interface in determining the contact resistance is described here. The contacts were formed by the deposition of several thousand angstroms of zinc onto p-type GaAs (Na=4×1018 cm−3) substrates by evaporation in an ultrahigh vacuum system. The nonlinear current–voltage characteristics of as-deposited samples changed to linear characteristics after annealing the samples up to 300 °C. The specific contact resistivities (ρc) as determined by four-point probe were typically 2×10−4 Ω cm2. Further annealing of the samples beyond 300 °C changed the linear current–voltage characteristics to nonlinear. The Auger depth profiles on samples which were as-deposited, annealed at 300 °C and annealed up to 500 °C explain the variations in the electrical characteristics. If preferential Zn diffusion into GaAs at 300 °C caused the Ohmic behavior, further heating up to 500 °C resulted in ZnO formation degrading both the electrical and structural properties.
Reactively sputtered AlN films for GaAs annealing caps
Authors: Este G. , Surridge R. , Westwood W. D.
Published: July 2002

Films for capping GaAs during annealing of implant damage have been deposited by magnetron sputtering of an Al target in Ar/N2 mixtures in two systems. The N2 flow was adjusted to obtain nitride formation on the target; this required a flow rate of 5 sccm at sputtering pressures of 0.2–0.5 Pa. The AlN deposition rate in N2 was approximately 10% of the Al rate in an argon discharge but increased by 30% as the fraction of Ar in the gas flow increased from 0 to 0.5. The film stress also varied with this fraction; compressive stress decreased and became tensile at a value of approximately 0.4. X-ray analysis showed all the films were single phase AlN with a lattice constant c=4.970 Å and had a preferred orientation with the c axis near the substrate normal. Undoped, semi-insulating GaAs wafers showed no decrease in resistance after rapid thermal anneal with an AlN cap deposited in one sputtering system. Annealing of AlN caps from the other system caused p-type conductivity in the GaAs which were shown by photoluminescence, SIMS, and Hall measurements to result from a Zn concentration of 1014 cm−2 arising from Zn vapor pressure in the sputtering system due to earlier depositions of ZnO. The sticking coefficient of Zn to the GaAs surface increased 1000 times by exposure of the GaAs to an oxygen plasma prior to deposition of the capping layer.
Toward quantification of thin film morphology
Authors: Messier Russell
Published: July 2002

Before any meaningful quantitative understanding of thin film growth morphology can be developed, a sufficiently detailed model must be established. For the case of films deposited under low mobility conditions, the model of the internal void networks, which are the morphology, is a fractal construction based upon the random competition for cone growth. The origin of the development of cones is a natural consequence of the random ballistic aggregation process. Both current and future approaches to quantitative measurement of this morphological model are discussed and include a series of direct (scanning electron, transmission electron, and field ion and optical microscopy) and indirect (spectroscopic ellipsometry, image enhancement and analysis of morphology photographs, small angle x-ray and electron scattering, and computer simulations of film growth) characterization techniques. It is shown how quantitative preparation–property relations in thin films will have to first start with a quantitative description of the film morphology.
Microstructures of thin sputtered amorphous Tb0.26Fe0.74 and polycrystalline Fe films
Authors: Nakahara S. , Hong M. , van Dover R. B. , Gyorgy E. M. , Bacon D. D.
Published: July 2002

A transmission electron microscope was used to characterize the microstructure of Te0.26Fe0.74 and Fe films obtained by magnetron and dc diode sputtering techniques. The films obtained by magnetron sputtering were very smooth, whereas those by diode sputtering were not smooth but islandlike, similar to the columnar structure. The microstructures were further examined by varying the pressure of argon gas. In both sputtering systems, an increase in the pressure promotes a tendency of the columnar structure to form.
Growth, nucleation, and electrical properties of molecular beam epitaxially grown, As-doped Ge on Si substrates
Authors: Sheldon P. , Yacobi B. G. , Asher S. E. , Jones K. M. , Hafich M. J. , Robinson G. Y.
Published: July 2002

Epitaxial Ge is grown on (100)Si substrates by molecular beam epitaxy (MBE). The effect of various MBE growth conditions on both the nucleation and morphology of Ge grown on Si is studied by Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and reflection high-energy electron diffraction (RHEED). These studies indicate that, at the substrate temperatures examined (300–600 °C), heteroepitaxy of Ge on Si favors three-dimensional growth, which is enhanced by both higher growth temperatures and substrate preparation techniques that leave residual surface contamination. Heavily doped n+ Ge layers are obtained using an elemental As source. The electrical properties of these films are evaluated by Hall–van der Pauw measurements. Growth temperatures of 250 °C and optimum As:Ge flux ratios yield electron concentrations as high as 2.5×1020 cm−3. Secondary ion mass spectroscopy (SIMS) and Hall effect data show that for As concentrations which exceed this optimum level, a decrease in both the electron concentration and drift mobility is observed, indicating the presence of electrically inactive As.
A spectroellipsometric investigation of the effect of argon partial pressure on sputtered palladium films
Authors: Sullivan Brian T. , Parsons R. R.
Published: July 2002

The microstructure of palladium thin films prepared by dc planar magnetron sputtering at low deposition temperatures was investigated as a function of the argon partial pressure. The films were characterized by spectroellipsometry, electron microscopy, and x-ray diffraction. Below a transition pressure Pt≂15 mTorr, the films consisted of densely packed grains, corresponding to the zone T region in Thornton’s structure zone model. Above this transition pressure the films developed into a more voided columnar structure, characteristic of a zone 1 region. A microstructural analysis of the spectroellipsometric data indicated a general trend to increased porosity and microroughness of the films with higher argon pressures. Furthermore, the effective medium theory of Sen, Scala, and Cohen (SSC), relevant for a random coated-particle microstructure where the grains are optically isolated from each other, was required to describe the films prepared with argon pressures above Pt. The zone 1 region was therefore best described optically as a random coated-particle microstructure where the microroughness and porosity varied with the argon pressure. Spectroellipsometry, which is sensitive to the film microstructure, was able to identify the zone T/zone 1 transition through the changes in the pseudodielectric function of the Pd films. Electron microscopy confirmed that for the thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries, thus further supporting the random coated-particle basis of the SSC theory.
Effect of negative substrate bias on the film structure and magnetic properties in sputter-deposited Co–Cr films
Authors: Ohkoshi Masatoshi , Kusuda Tetsuzo
Published: July 2002

Film structure and magnetic properties are investigated in Co–Cr films sputter deposited with an applied substrate bias voltage. Large grains with c-axis orientation are found at negative bias between 40 and 75 V. Coercivity decreases remarkably in these films. These changes in film structure and magnetic properties by applying low bias originate from the moderate bombardment by Ar ions under low oxygen contamination as well as little Ar incorporation. With further increase of negative bias, saturation magnetization decreases to the bulk value and perpendicular magnetic anisotropy decreases to zero, because violent ion bombardment yields complete solid solution of Co and Cr. Temperature dependence of saturation magnetization in zero bias Co–Cr films with perpendicular magnetization reveals a compositional inhomogeneity in which concentration of Cr distributes between 10 and 30 at. %. The compositional inhomogeneity is eliminated by the substrate bias.
The C K
L
L first-derivative x-ray photoelectron spectroscopy spectra as a fingerprint of the carbon state and the characterization of diamondlike carbon films
Authors: Mizokawa Yusuke , Miyasato Tatsuro , Nakamura Shogo , Geib Kent M. , Wilmsen Carl W.
Published: July 2002

The C KLL spectra from natural diamond, graphite, and single-crystal β-SiC have been investigated using x-ray photoelectron spectroscopy and first-derivative x-ray excited Auger electron spectroscopy (XAES). It is shown that the XAES spectra is essentially the same as that obtained with conventional AES with the added benefits of no electron beam (e-beam) damage, enhanced fine structure, and the simultaneous acquisition of the C 1s and valence-band spectra. The C KLL XAES fine structure provides a fingerprint of the carbon bonding state and the C 1s and valence-band spectra provide insight into the origin of this fine structure. Diamondlike carbon films fabricated by hydrogen gas reactive sputtering of graphite on Si were also investigated. The XAES C KLL spectra in conjunction with the valence-band spectra verifies the tetrahedral C–C bonding in these films even though the AES spectra shows a graphitelike structure; indicative of e-beam damage.
Mass spectrometric and ion energy diagnostics in the study of plasma etching and polymerization
Authors: Ferreiro L. M. , Ernie D. W. , Evans J. F.
Published: July 2002

Mass spectrometric sampling of ions and neutrals from water, hydrogen, and styrene plasmas sustained by 13.56-MHz radio frequency excitation have been studied using a reactor equipped with a small (80–200 μm) sampling orifice leading to a quadrupole mass spectrometer. The apparatus is described, including a discussion of the use of retarding grids to measure ion energy distributions in the sheaths of these plasmas. For both etching and polymer deposition in the pressure regime of 1–50 mTorr, evidence is provided from the mass spectra and ion energy spectra suggesting that the sheath is not collisionless. The data indicate that collisionally activated dissociation and high-energy ion–molecule reactions occur in the sheath, while collisional stabilization occurs in the bulk of the discharge.
Thermal annealing effects on amorphous radio frequency sputtered Cd0.95Fe0.05Te thin films
Authors: Alvarez-F. Octavio , Mendoza-Alvarez J. G. , Sanchez-Sinencio F. , Romero Saul , Vidal Miguel Angel
Published: July 2002

Cd0.95Fe0.05Te thin films have been grown by rf sputtering. Electron diffraction techniques show that the films are amorphous when deposited onto glass substrates at room temperature. The samples were heated for 1 h, in a forming gas atmosphere, at different temperatures in the range 50–450 °C. X-ray studies show that there is a phase transition from amorphous to crystalline phase in the 300–350 °C temperature range. Electrical conductivity of the annealed samples was measured as a function of temperature. The conductivity is thermally activated and the activation energy Ea after annealing is always greater than the one measured in the as-grown samples. Ea remains almost constant, around 0.6 eV, for samples annealed in the 100–450 °C temperature range. This value of 0.6 eV is probably associated to a deep donor level.
Thin-gate low-pressure chemical vapor deposition oxides
Authors: Freeman Dean W.
Published: July 2002

Thin-gate oxides were deposited using dichlorosilane (DCS) and nitrous oxide. The films were characterized both chemically and electrically. The results show that a film using a low N2O/DCS ratio is silicon rich and has a large number of electron traps in the as-deposited state. Films with a large N2O/DCS ratio are not silicon rich but also have a large number of electron traps. Avalanche injection data indicate that the traps are in the bulk of the film, as opposed to being surface state traps, suggesting that a high-temperature cycle would anneal out the bulk traps.
Oxidation of thin WSi2 overlayers on Si(111)
Authors: Nguyen Tan T. A. , Azizan M. , Derrien J.
Published: July 2002

The mechanisms and kinetics of oxidation of thin WSi2(0001) epitaxial layers (∼150 Å) prepared by annealing W deposits on Si(111)(7×7) surfaces have been studied by ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy (XPS), and x-ray induced Auger electron spectroscopy. Oxidation was carried out at room temperature and at 700 °C, under 2×10−5 mbar oxygen pressure. A Si(111) sample, submitted to the same oxidation procedure, was used as a reference. The energy positions and the intensity variations of the core levels (Si 2p, W 4f) and XPS valence bands indicate for both oxidation conditions (low and high temperature) the formation of silicon oxide on top of the WSi2 layer, while the composition and the electronic structure of this silicide are unaffected. Oxygen is bonded to Si only and no W–O bond is detected. The nature of the silicon oxide overlayer depends on the temperature. At room temperature, the oxide derived Si 2p feature corresponds to a dominant O–Si–O bonding, to be compared to the multiple configuration observed with the Si(111) face. Additional experiments with one monolayer of W deposited on Si(111) show an enhancement of oxidation and migration of Si atoms from the bulk Si to the surface. The UPS spectra and the work function measurements agree with an atomic chemisorption of oxygen. At 700 °C, silicon dioxide grows on the surface. In this case, the Si KL2L3 Auger transition, owing to its larger energy shift and a larger escape depth in comparison with the Si 2p, reveals the presence of a 3–5 Å suboxide region between the SiO2 layer and the underneath WSi2. The oxidation rates are comparable to those of Si(111).
Characterization of anodic sulfide films on Hg0.78Cd0.22Te
Authors: Strong R. L. , Luttmer J. D. , Little D. D. , Teherani T. H. , Helms C. R.
Published: July 2002

Anodic sulfide films were grown on HgCdTe and studied by Auger electron spectroscopy, surface analysis by laser ionization, Rutherford backscattering spectroscopy, Raman and photoluminescence spectroscopy, and high-resolution transmission electron microscopy to determine their elemental composition and their chemical and physical structure. This information, when coupled with a knowledge of the possible chemical reactions at the interface between the film and the HgCdTe substrate, explains why anodic surface films are more thermally stable than anodic oxide films.
New phases of manganese achieved by epitaxial deposition
Authors: Heinrich B. , Arrott A. S. , Liu C. , Purcell S. T.
Published: July 2002

Mn is deposited on the (0001) surface of Ru and the (100) surfaces of Fe and Ni in a PHI 400 molecular-beam epitaxy system. The first two layers of Mn on Ru (0001) maintain the close-packed spacing of the Ru substrate. By comparison with other forms of Mn, this is an expanded structure. Beyond two layers, Mn maintains epitaxy, forming a denser phase which is most likely the hexagonal Zn2Mg structure, but possibly the fcc Cu2Mg structure, or a stacking fault variant of these two quite similar structures. The basic unit of both the Zn2Mg and Cu2Mg structures is the hexatetrahedron which is found also in the more complex α-Mn structure. In each of these cases Mn appears to be an intermetallic compound with itself. Mn on Fe(100) forms epitaxially in the bcc phase. Mn on Ni(100) forms in a complex phase which has yet to be deciphered. The atomic magnetic moments of the Mn atoms in these phases are deduced from measurements of the exchange splitting of the 3s peak in the x-ray photoelectron spectra. The splitting of the 3s peak is surprisingly insensitive to the Mn structure, but the intensity of the split-off peak reflects the dependence of magnetic moment to atomic volume.
A photoemission survey of the electronic properties of ternary semimagnetic semiconductor alloys
Authors: Wall A. , Chang S. , Philip P. , Caprile C. , Franciosi A. , Reifenberger R. , Pool F.
Published: July 2002

We review the results of a number of recent synchrotron radiation photoemission studies of the electronic structure of concentrated ternary semimagnetic semiconducting alloys. The materials examined include Cd1−xMnxS, Cd1−xMnxSe, Cd1−xMnxTe , Zn1−xMnxSe, and the narrow-gap Hg1−xMnxTe, Hg1−xMnxSe, and Hg1−xFexSe. Photon-energy-dependent photoemission methods are being used to probe the elemental and orbital contribution to the valence states. The new information is stimulating novel theoretical work on the electronic structure and lattice stability of these semiconductors.
Retention of hydrogen in graphite
Authors: Langley R. A.
Published: July 2002

The retention of hydrogen in POCO AXF-5Q graphite has been measured at room temperature as a function of fluence and flux for H+2 ions at energies from 250 to 500 eV provided by a glow discharge. More than 2×1018 H/cm2 has been retained, and no indication of saturation has been observed to a fluence of 5×1019 H/cm2. In this experiment retention was found to increase linearly with fluence for constant flux. A flux dependence was observed; i.e., the retention rate was observed to decrease monotonically as the flux increased. A changeover experiment, deuterium to hydrogen, was conducted; the results show that significant changeover occurs (i.e., about 30% changeover for a fluence of 5×1017 D/cm2).
Surface analysis of bulk polymers using single- and multiple-photon ionization
Authors: Schühle U. , Pallix J. B. , Becker C. H.
Published: July 2002

The surface analysis by laser ionization (SALI) technique has been applied to the chemical analysis of bulk solid polymer surfaces. Surface material was removed by a pulsed rare-gas ion probe beam at ∼7 keV and sputtered neutral molecules were photoionized by pulsed coherent radiation at 118 nm (10.5 eV) or 248 nm (5.0 eV). Photoions were then extracted into a reflecting time-of-flight mass spectrometer. The ion beam dose during analysis was kept below significant damage levels (<1013 primary ions/cm2), indicative of the very high sensitivity. The single-photon ionization (118 nm) resulted in much more extensive and representative mass spectra than for the multiphoton ionization, reflecting the fact that it is a relatively ‘‘soft’’ ionization technique. Very distinct and readily interpretable mass spectra are shown for poly(tetrafluoroethylene), the polyamide nylon 66, and poly(ethylene-glycol)-monostearate. Where comparison secondary ion mass spectra are available, these SALI spectra with one-photon ionization compare quite favorably.
Growth and luminescence spectroscopy of a CuCl quantum well structure
Authors: Williams R. Stanley , Shuh David K. , Segawa Yusaburo
Published: July 2002

A structure of the type CaF2/CuCl/CaF2, in which the confined layer is 150 Å thick, has been grown on a Si(111) surface by molecular beam epitaxy in ultrahigh vacuum. The optical properties of the CuCl film have been characterized by low-temperature photoluminescence as a function of excitation density. Striking differences in the excitonic emissions are observed between the quantum well structure and a bulk single crystal of CuCl, and are discussed in terms of film purity and thickness.
Diffusion of boron, phosphorus, and arsenic implanted in thin films of cobalt disilicide
Authors: Thomas O. , Gas P. , d’Heurle F. M. , LeGoues F. K. , Michel A. , Scilla G.
Published: July 2002

The diffusion of boron, phosphorus, and arsenic in layers of CoSi2 has been investigated. In order to limit effects due to interfaces and grain boundaries, the layers used were extremely thick, ∼900 nm. The dopants were introduced via implantation to a depth of ∼70 nm. Values of the activation energy for the lattice diffusion of both boron and phosphorus were obtained. In contrast to these two elements arsenic was found to be almost totally immobile. Some implications of these results for practical applications are briefly discussed.
A new growth enhancement in thin SiO2 formed by rapid isothermal oxidation of silicon
Authors: Singh R. , McGruer N. E. , Rajkanan K. , Weiss J. H.
Published: July 2002

Rapid growth of thin SiO2 (<100 Å) on silicon is observed following annealing in argon. The growth enhancement is active for a short time following argon anneals, and does not depend on oxide thickness in the sub-100-Å regime. Also, the enhancement may be reset many times, by annealing, for a growing oxide film. Growth kinetics of the enhancement are different than those of the often discussed initial growth regime enhancement. The anneal time required to produce enhanced growth is a factor of 10 less than that required to reduce interface trap density. Study of the phenomenon at time scales not accessible through furnace processing is made possible by the use of a rapid isothermal processor. The annealing process alters the Si–SiO2 system in some way, as yet undetermined, that affects the growth of the oxide in the thin regime. In this paper, we present the results of in situ anneal induced growth enhancement during rapid thermal oxidation of n-type (100) silicon. These results should shed a new light on dry thermal oxidation of silicon.
Effect of substrate preparation on the structure and chemisorption properties of Pd/MgO model catalyst
Authors: Henry C. R. , Poppa H.
Published: July 2002

Pd/MgO model catalysts are prepared by vapor deposition of Pd particles on MgO thin films which are deposited, at different temperatures, on UHV cleaved mica. MgO films and Pd particles are characterized in situ by Auger electron spectroscopy and energy-loss spectroscopy and ex situ by transmission electron microscopy. Successive temperature programmed desorption (TPD) of CO shows a different evolution of the morphology of the Pd particles deposited on MgO films prepared at low and high temperature. In addition, on MgO prepared at low temperature, the smallest particles show a continuous decay of CO adsorption during TPD due to contamination by support species.
Photoreflectance study of boron ion-implanted {100} CdTe
Authors: Amirtharaj P. M. , Odell M. S. , Bowman R. C. , Alt R. L.
Published: July 2002

We have studied ion-implanted {100} CdTe using the contactless technique of photoreflectance. The implantations were performed using 50–400 keV boron ions to a maximum dosage of 1.5×1016 cm−2 and the annealing was accomplished at 500 °C under vacuum. The spectral measurements were made at 77 K near the E0 and E1 critical points; all the spectra were computer fitted to Aspnes’ theory. The spectral line shapes from the ion damaged, partially recovered, and undamaged or fully recovered regions could be identified and the respective volume fraction of each phase was estimated.
Electrical properties of intrinsic p-type shallow levels in HgCdTe grown by molecular-beam epitaxy in the (111)B orientation
Authors: Boukerche M. , Sivananthan S. , Wijewarnasuriya P. S. , Sou I. K. , Faurie J. P.
Published: July 2002

The electrical properties of the unintentionally doped p-type HgCdTe material as grown in the (111)B orientation by molecular-beam epitaxy are revised. The analysis of the Hall coefficient in the whole temperature range with a model based on the two-band nonparabolic Kane model, a fully ionized compensating donor concentration, and two independent discrete acceptor levels is presented. The donor compensation is found to be much lower than before, in agreement with the latest study of extrinsic doping by indium. A defect level with an energy of 30 to 50 meV is found necessary to explain properly some of the crystals’ data. The results of a three-carrier band modeling of the Hall constant versus field are also presented for one sample and are in very good agreement with the expected band structure of the material. These results show that important improvements have been made recently in the control of stoichiometry during growth.
Study of field-emitting microstructures using a scanning tunneling microscope
Authors: Niedermann Ph. , Renner Ch. , Kent A. D. , Fischer O/.
Published: July 2002

Field emission from broad metal cathodes is known to be strongly enhanced at a small number of emitting sites per cm2 compared to the expected Fowler–Nordheim emission from ideal, flat surfaces. We have operated a scanning tunneling microscope (STM) in the field emission regime (typical tip voltage: +80 V) and measured the local field emission strengths and variations on niobium samples. With a modulation technique, which is an adaptation of the standard work function measurement, maps of the field enhancement factor β have been obtained. An example of an emission site is presented where STM topograph and β map are compared with a secondary electron microscope image and with field emission data obtained in a standard way using high-voltage anodes. This demonstrates the capability of a scanning tunneling microscope to localize enhanced field emission sites (with typical β values of 50 in the present work) with high spatial resolution and to study surfaces down to the limit β=1.
Pressure-dependent damping of a particle levitated in vacuum
Authors: Hinkle L. D. , Kendall B. R. F.
Published: July 2002

A novel method of levitation, using an actively controlled electric field, launches, captures, and stably suspends a microscopic (∼15 μm) particle in high vacuum. While held to within one diameter in the vertical direction, the particle is allowed to oscillate nearly freely in the horizontal plane under the influence of a central restoring force. The damping of horizontal oscillations was measured over the pressure range from 10−2 to 10−8 Torr. The damping was observed to be proportional to pressure down to less than 10−6 Torr, where residual (pressure independent) damping became significant. An absolute high vacuum gauge based on the pressure-dependent damping observed with this apparatus could operate linearly throughout at least a six decade range. A prototype gauge design is suggested.
Ion-assisting magnetron sources: Principles and uses
Authors: Window B. , Harding G. L.
Published: July 2002

The design and performance of magnetron sources which provide at the substrate not only the flux of sputtered atoms but also fluxes of electrons and ions from the plasma are described. This energetic particle bombardment (which is directed to the substrate by an unbalanced magnetic field design) can be beneficial, as when it is used to ion assist the growth of the depositing thin film, or deleterious, e.g., by providing extra heating. Applications of unbalanced magnetrons to investigate the technology of magnetron sputtering are described. Ion assistance of the growing film increases the biaxial compressive stress in the growing film due to an atomic peening process. The lattice strain produced by the stress can be measured using x-ray diffraction, and can be used to quantify the degree of ion assistance. Effects studied in films of refractory metals include the increase in stress until plastic flow occurs during growth, changes in preferential orientation, the effectiveness of the different gases Ar and Xe in producing stress, energetic neutral bombardment, and moderation of sputtered atoms. New results are presented here for the temperature dependence of the stress production in molybdenum films. The application of unbalanced magnetrons to industrial deposition processes is discussed.
Growth, annealing, and characterization of HgZnTe liquid phase epitaxy layers
Authors: Sher Ariel , Tsigelman Alex , Weiss Eliezer , Mainzer Nilly
Published: July 2002

Epitaxial layers of Hg1−xZnxTe(0.12≤x≤0.25) were grown by horizontal liquid phase epitaxy technique on closely lattice matched CdZnTe substrates. The growth conditions in which the rate of growth was limited by the diffusion of the solutes in the liquid were found. Post-growth annealing study of the epilayers revealed the ability to control the epilayers electrical properties by in-diffusion of Hg. The annealing at the temperature of 340 °C resulted in p-type epilayers with hole concentration of ≊1×1016 cm−3 , mobility of 380–600 cm2 /V s and lifetime of 20–40 ns (for long-wavelength infrared epilayers), measured at 77 K. The results of the annealing at the temperature of 220 °C were dependent on the annealing time and the substrates. n-Type epilayers were characterized, showing electron mobility dependence on the energy band gap and temperature. The results of preliminary experiments of ion implantation into the annealed, p-type epilayers are discussed.
Oxygen induced adhesion degradation at metal/polyimide interface
Authors: Shih Da-Yuan , Klymko Nancy , Flitsch Richard , Paraszczak Jurij , Nunes Sharon
Published: July 2002

The role of oxygen in affecting the adhesive bonding at the metal/polyimide (polyimide-on-metal) interface has been studied. Both pyromellitic dianhydride (PMDA) -oxydianiline (ODA) and biphenyl-tetracarboxylic dianhydride(BPDA) -p-phenylene diamine (PDA) based poly(amic acid) precursors were cast and fully imidized on metal surfaces of Cr, Cu, Ni, Co, Cu/Ni, and Cu/Co in a nitrogen atmosphere. The peel strengths at the polyimide-on-metal interface were measured, using a 90° peel test, immediately after curing, and then remeasured after annealing in either nitrogen (N2−≤100 ppm O2 ) or air (N2 –21% O2 ) at 350 °C for 1 h. Very little or no change in peel strength was measured after these samples were annealed in nitrogen, while significant adhesion degradations were measured on all metals after annealing in air. The loss of polyimide (PI) adhesion to the Cu or Co surface is attributed to metal catalyzed thermal–oxidative degradation of the PI at the metal/PI interface, as characterized by polyimide thickness reduction, Fourier transform infrared and x-ray photoelectron spectrometries. The rate of degradation of the PMDA-ODA films on Cu or Co is several times faster than that of the BPDA-PDA films.

The degradation products were characterized as CO2, CO, Cu carboxylate salts and a nitrile moiety entrapped in partially degraded PI films. The extent of degradation was found to increase with increasing oxygen content in the annealing ambient or with decreasing PI thickness, indicating that oxygen diffusion through the PI overcoating to the metal/PI interface plays a critical role in promoting degradation. On the Cr and Ni surfaces, such metal catalyzed degradation was not detected with our techniques, while some adhesion strength was still retained, a significant loss in adhesion strength was observed. This is probably due to oxidation of the metal underlayer causing debonding at the originally well adhered metal/PI interface. When all testing variables were held constant, the peel strength of a well adhered metal/PI joint is shown to increase with increasing peeling rate (crosshead speed). An increase of up to ∼40% in peel strength was measured when the crosshead speed was increased from a low speed of 0.05 mm/min to 10 mm/min. The locus of fracture of the as-cured films was cohesive, i.e., the fractured surface was located within PI, while for the thermal–oxidative degraded joint the failure mode was changed to adhesive.
ZnSexTe1−x films grown by pulsed laser deposition
Authors: Aydinli A. , Puente G. Contreras , Bhat A. , Compaan A. , Chan Alan
Published: July 2002

An XeCl excimer laser was used to grow thin polycrystalline films of the ternary alloy semiconductor, ZnSexTe1−x, on sodium-free glass substrates. The laser ablation/evaporation process has produced films spanning the entire compositional range with x values close to those of the original target. At a typical growth temperature of 300 °C, the grains possess orientations which vary from a predominant 〈111〉 for ZnTe to 〈311〉 for ZnSe with an increasing fraction of 〈311〉 as the ZnSe fraction increases. X-ray diffraction shows that the alloy lattice constant increases linearly with the x value, absorption measurements show band bowing similar to that observed in bulk single crystals, and Raman studies show that the lattice dynamics are characteristic of single-vibrational-mode behavior over the entire alloy range.
Boron contamination of surfaces in silicon microelectronics processing: Characterization and causes
Authors: Stevie F. A. , Martin E. P. , Kahora P. M. , Cargo J. T. , Nanda A. K. , Harrus A. S. , Muller A. J. , Krautter H. W.
Published: July 2002

Boron contamination has been detected by secondary ion mass spectrometry at almost every surface and interface in silicon microelectronics structures. Areal densities for boron are typically 102–1013 atoms/cm2 and can cause counterdoping if the boron is distributed by an anneal into a lightly doped n-type region. Boron was quantified by encapsulating the surface of the layer of interest with an identical layer and thereby retaining matrix homogeneity across the interface where the original surface is located. The origin of boron was shown to be airborne contamination. Boron in the atmosphere and the borosilicate glass in the high efficiency particulate air filters used in clean room construction have been identified as contamination sources. Accumulation of boron on a polysilicon surface follows a relationship similar to that for oxide growth. Processing with hydrogen, buffered HF cleaning of the surface, or growth of a removable SiO2 layer will reduce or eliminate boron from the silicon surface.
Commercial-scale application of plasma processing for polymeric substrates: From laboratory to production
Authors: Felts J. T. , Grubb A. D.
Published: July 2002

Large-scale application of plasma enhanced chemical vapor deposition (PECVD) and PECVD-like processes have been limited due to the inherent complexity and dependence of the reactor geometry and gas flow patterns on the process variables. Plasma diagnostics and robust experimental design have enabled large-area application of an organosilicon-based chemical plasma deposition process for application on rigid polymeric substrates (bottles, trays, etc.) and thinner (0.5 mil thick) polymeric films. The process was successfully transferred among four vacuum systems, each employing different electrodes, gas flow geometrics, and pumping configurations. Furthermore, desirable film properties were obtained at deposition rates in excess of 200 Å/s in the pilot scale roll-to-roll coater. In the pilot bottle coater, large loads of bottles (117, 32 oz containers) were uniformly coated on a routine basis. A historical account of the process development and technical hurdles, along with experimental data from the four reactors studied, will be presented.
Adsorption and electron stimulated desorption of NH3/TiO2(110)
Authors: Diebold U. , Madey T. E.
Published: July 2002

Adsorption and electron stimulated processes of NH3 on rutile TiO2(110) have been studied by means of x-ray photoemission spectroscopy (XPS) and low-energy ion scattering (LEIS). Defects, mostly surface oxygen vacancies, can be produced easily on TiO2 surfaces by thermal treatment or by rare gas ion sputtering. We have used three differently prepared TiO2 surfaces to study the influence of the substrate defect structure on the interaction with NH3: a stoichiometric surface, a thermally treated (slightly oxygen deficient), and a sputtered (highly oxygen-deficient) surface. The adsorption behavior of NH3 on all these surfaces is quite similar. NH3 adsorbs molecularly, with a saturation coverage of ∼0.16–0.19 monolayers, the latter for a highly oxygen-deficient surface. The electron stimulated desorption (ESD) behavior is quite different: In the limit of a stoichiometric surface, electron irradiation induces the desorption of NH3 molecules, with a desorption cross section of ∼ 1 × 10−16 cm2. When the highly oxygen-deficient TiO2 surface is used as substrate, besides desorption, electron stimulated dissociation of NH3 takes place, with atomic nitrogen being the final product of the dissociation process. This atomic nitrogen is adsorbed in subsurface sites, as confirmed by angle-resolved XPS. Under certain conditions, an electron stimulated formation of surface nitride is observed. These measurements provide direct evidence for the role of surface defects in electron stimulated reaction pathways.
Electron tunnel sensors
Authors: Kenny T. W. , Kaiser W. J. , Reynolds J. K. , Podosek J. A. , Rockstad H. K. , Vote E. C. , Waltman S. B.
Published: July 2002

We have used the extreme sensitivity of electron tunneling to variations in electrode separation to construct a novel, compact displacement transducer. Electrostatic forces are used to control the separation between the tunneling electrodes, thereby eliminating the need for piezoelectric actuators. The entire structure is composed of micromachined silicon single crystals. Applications of the tunneling displacement transducer to the measurement of acceleration and infrared signals are discussed. Measurements of acceleration and infrared sensitivity are reported.
Molecular-dynamics study of film growth with energetic Ag atoms
Authors: Gilmore C. M. , Sprague J. A.
Published: July 2002

Three-dimensional molecular-dynamics simulation of the growth of silver (Ag) atoms on an Ag (111) oriented substrate has been conducted as a function of incident atom energy and temperature. Incident atom energies of 0.1 eV per atom resulted in the formation of epitaxial islands that coalesced to form a continuous thin film. Increasing the incident atom energy promoted layer-by-layer growth, and with an incident atom energy of 10 eV per atom the film growth was nearly layer-by-layer. For the 10-eV incident atom energy with a 330-K substrate temperature a small amount of interface mixing was observed, but the mixing was eliminated by lowering the substrate to 30 K. The interface mixing process occurred by an exchange process between the energetic atom and a surface atom. Increasing the incident atom energy to 20 eV per atom increased the amount of interface mixing, but the interface mixing could not be eliminated by lowering the temperature of the substrate. This indicates that the mixing process is ballistically activated and thermally assisted. Increasing the incident atom energies to 40 eV per atom resulted in the mixing extending to the second layer of substrate atoms; however, the mixing was found to occur by multiple unrelated exchanges between adjacent layers. All deposited atoms were observed to form epitaxial layers; although stacking faults were observed.
Frizzed appearance of steps in tunnel microscopy on Cu(100) and vicinal Cu(11n) surfaces
Authors: Giesen M. , Frohn J. , Poensgen M. , Wolf J. F. , Ibach H.
Published: July 2002

Steps on Cu(100) and various vicinal Cu(11n) surfaces were studied with the scanning tunneling microscope and the kink concentrations are determined using a recently developed method. As expected, the kink concentration in steps on the (117) and the (1 1 11) surface is lower than for steps on the (100) surface due to the repulsive interaction between steps at small distances. On the (1 1 19) surface, however, steps have a larger kink concentration. The result is discussed in the context of the recently discovered attractive interaction between steps for intermediate step distances.
Deposition, characterization, and device development in diamond, silicon carbide, and gallium nitride thin films
Authors: Davis Robert F.
Published: July 2002

The extreme thermal and electronic properties of diamond, SiC, and GaN provide combinations of attributes which lead to the highest figures of merit for any semiconductor materials for high-power, high-temperature, high-frequency, and optoelectronic applications. The methods of deposition and the results of chemical, structural, microstructural and electrical characterization, and device development are reviewed for thin films of these three materials. Problems and areas of future research are also noted.