bluuebunny/crossref_metadata_2025 huggingface dataset:
(100) and (111) Ni films epitaxially grown on Cu by the metal–metal epitaxy on silicon technique near room temperatures
Authors: Chang Chin-An
Published: July 2002

A growth technique is described which uses the Cu films epitaxially grown on Si as seed layers for the further epitaxial growth of other metals. The technique, metal–metal epitaxy on silicon (MMES), is illustrated with the growth of both (100) and (111) Ni films. Ni, being a face-centered cubic (fcc) metal, tends to grow in the (111) orientation on various substrates, including (100) Si. The (100) Cu/Si structure, however, allows the growth of Ni in the (100) orientation near room temperatures using electron-beam evaporation in a vacuum of low 10−7 Torr. A minimal thickness of the Cu seed layer needed for the growth of (100) Ni is found to be between 20 and 50 Å. Using the (111) Cu/Si substrates, (111) Ni is observed. Both the single layer, Ni/Cu/Si, and the double layer, Cu/Ni/Cu/Si structures have been grown with controlled orientations. The latter allows the growth of periodic Cu–Ni structures with ultrathin layer thicknesses. The periodic structures of a Cu(50 Å)–Ni(25 Å) superlattice is well resolved for the films deposited on (100) and (111) Cu/Si, and on Cu/glass. The last structure shows both the (100) and (111) diffraction patterns of the superlattice, with well resolved satellite peaks. Heating the Cu–Ni structures shows an interesting orientation dependence for the interactions, with a higher outdiffusion rate of Cu through Ni for the (111) orientation than the (100) one. This is opposite of that observed for either the outdiffusion of Si through Au using single crystal Si substrates, or the reaction rate of Cu–Si for the Cu films epitaxially grown on Si. An interface model is used to explain the results observed. Possible applications of the epitaxial Ni films thus grown are suggested.
Microstructure of yttria-stabilized zirconia overcoats for thin film recording media
Authors: Kao A. S. , Hwang C.
Published: July 2002

The microstructure of reactively sputtered zirconia overcoats (50 nm thick) for magnetic recording media is examined by transmission electron microscopy (TEM). The micrographs show that the microstructure can be altered from a porous to a tightly packed, and then to a coarse-grained, structure depending on the oxygen partial pressure used during film deposition. The porous film deposited under oxygen-deficient conditions resulted in structural relaxation giving reduced film stress and hardness as the continuous voids developed along intergrain regions. Concurrently, the strength of this overcoat film against wear fracture deteriorated due to the presence of these voids. Increasing oxygen partial pressure during film deposition heals these intergrain voids and leads to the coarsening of the cubic-phase grains. At oxygen partial pressure of 0.04 Pa, a relaxed film structure is again observed. However, it results from the low defect density and lattice strain within individual zirconia grains as the film approaches ideal stoichiometry. This relaxation effect, in turn, reduces the stress, hardness, and wear resistance of the overcoat film. Between these two extremes, a tightly packed, fine-grained film microstructure with optimum hardness and wear strength can be obtained by deposition at oxygen partial pressure of 0.02 Pa.
Characterization of the n=1 image state on Ni(111) with two-photon photoemission
Authors: Hamza Alex V. , Kubiak Glenn D.
Published: July 2002

The binding energy and E(k∥) dispersion of the n=1 image potential state have been measured on Ni(111) using angle-resolved two-photon photoemission. The binding energy, εn=1, is found to be 0.8±0.1 eV. The E(k∥) dispersion relation is well described by an effective mass m*/me, of 1.0±0.1, in disagreement with earlier momentum-resolved inverse photoemission results, but in agreement with theoretical predictions based on a phase analysis of the n=1 image state wave function. Two-photon photoemission spectra were also recorded for Ni(111)-p(2×2)-O, showing the disappearance of the image state and the emergence of a weak, broad, nondispersive feature attributable to two-photon photoemission from states originating near the Fermi level.
Ion-irradiation-induced suppression of three-dimensional island formation during InAs growth on Si(100)
Authors: Choi C.-H. , Hultman L. , Barnett S. A.
Published: July 2002

Nucleation and growth of InAs on Si(100) substrates during ion-assisted deposition has been investigated. Reflection high-energy electron diffraction studies showed that InAs films nucleated by the Stranski–Krastanov (SK) mechanism. Ar ion irradiation with energies E near 30 eV and a flux of 4 ions per deposited atom prolonged the layer-by-layer stage of SK nucleation. The transition from layer-by-layer to island growth was at 2–3 monolayers (ML) for growth temperature Ts=380 °C and E=13 eV. With Ts=380 °C and E=28 eV, on the other hand, layer-by-layer growth was maintained up to ∼10 ML. A further increase in E to 38 eV reduced the transition coverage to ∼7 ML. In addition, epitaxial temperatures were reduced from >345 to <250 °C by increasing the Ar ion energy E from 13 to 38 eV. Cross-sectional transmission electron microscopy studies of 500 nm thick films showed that increasing E from 13 to 28 eV during the nucleation stage smoothened the surface and improved the crystalline perfection. The effect of ion bombardment on the nucleation mechanism is explained as being due to ion-induced dissociation of three-dimensional islands and ion-enhanced surface diffusion.
The importance of free radical recombination reactions in CF4/O2 plasma etching of silicon
Authors: Dalvie M. , Jensen K. F.
Published: July 2002

The importance of free radical recombination reactions of F in CF4/O2 plasma etching of Si is explored in a combined experimental and modeling study of a single wafer etcher. The F atom concentration profiles in the reactor, as well as the silicon etch rate profiles, are strongly influenced by the recombination reactions. The surface recombination reaction is more important than the gas phase recombination reactions in determining overall system behavior. The effects of the homogeneous as well as heterogeneous recombination reaction diminishes with increasing flow rate. This is due to combined residence time and transport effects.
Molecular beam epitaxy/atomic layer epitaxy growth processes of wide-band-gap II–VI compounds: Characterization of surface stoichiometry by reflection high-energy electron diffraction
Authors: Yao T. , Zhu Z. Q. , Uesugi K. , Kamiyama S. , Fujimoto M.
Published: July 2002

A good agreement is found between the observed temporal dependence of the reflection high-energy electron diffraction (RHEED) intensity variation of a specular spot and the calculated temporal dependence of surface coverage during sublimation and adsorption processes in atomic layer epitaxy. Here the surface coverage is calculated on the basis of a phenomenological model in which precursor states are taken into account. The RHEED oscillation behavior during molecular beam epitaxy (MBE) growth of Zn chalcogenides is investigated for various growth conditions. The RHEED intensity saturates at a certain level and the saturation level is closely correlated with the surface stoichiometry or the surface coverage. It is concluded that the RHEED intensity variation corresponds to the change in surface coverage during ALE and MBE growth. It is possible to characterize the surface stoichiometry during atomic layer epitaxy (ALE) and MBE growth by RHEED.
The influence of crystallographic orientation on gallium incorporation in HgCdTe grown by metalorganic chemical vapor deposition on GaAs
Authors: Korenstein R. , Hallock P. , MacLeod B. , Hoke W. , Oguz S.
Published: July 2002

The influence of the crystallographic orientation on gallium incorporation in HgCdTe films grown on GaAs substrates was investigated. It was found that growth on the (111)B orientation results in approximately 100 times more gallium incorporation than on the (111)A orientation and the (100) orientation falls in between the other two. The results can be explained in terms of the chemical reactivity of each surface. Chemical reactions between the GaAs back surface and the metalorganic reagents are believed to be the source of gallium doping.
Estimation of film thickness from the background signal in x-ray photoemission spectroscopy
Authors: Ogama T. , Horikawa T.
Published: July 2002

A nondestructive estimation of the thickness of a uniform overlayer has been investigated using x-ray photoemission spectroscopy (XPS), which is an application of Tougaard’s formalism. It has been shown that it is possible to estimate the thickness of an overlayer existing on a semi-infinite underlayer, by measuring the ratios of the peak area to the background signal on the high binding energy side of a photoelectron peak produced by an element existing in an underlayer before and after removing the overlayer. Especially when the inelastic mean free path of a photoelectron in an overlayer and an underlayer can be approximated equal, the relation between those ratios and the overlayer thickness is expressed in a very simple mathematical form. This method has been applied to various thickness of a-Si:H overlayers on SiNx formed by plasma chemical vapor deposition (CVD) method. A good linear correlation has been obtained between the thickness estimated by this method and that estimated from the deposition time, and thus the validity of this method has been shown.
A miniature x-ray compatible sputtering system for studying i
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c thin film growth
Authors: Zheng J. Q. , Shih M. C. , Wang X. K. , Williams S. , Dutta P. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We describe a miniature sputtering system incorporating an unconventional magnetron gun and a right angle sputtering geometry. The design essentially eliminates the negative ion resputtering effect encountered in the sputtering of high Tc oxide films. The geometry is compatible with the in-plane and conventional θ–2θ diffraction geometries and a chamber with two appropriate sector x-ray windows has been constructed and operated at a synchrotron. Detailed data on the performance of the sputtering gun are presented.
Effusion cell orientation dependence of molecular beam epitaxy flux uniformity
Authors: Shiralagi K. T. , Kriman A. M. , Maracas G. N.
Published: July 2002

The effect of effusion cell orientation on the uniformity of the flux distribution during molecular-beam epitaxy growth is modeled numerically. By pointing the effusion cell axis 30 mm away from the center of the substrate, thickness variation over a 3 in. wafer can be reduced from 23% to 11% for growth with substrate rotation. The corresponding reduction in the total flux is only 8%. Uniformity on a rotating substrate is improved when the effusion cells are positioned with the peak flux directed toward the substrate edge closest to the effusion cell. Without rotation, uniformity requires a peak flux directed at the far side. Source–substrate configurations are determined which maximize uniformity on large diameter wafers. Predictions of the model are verified by experiments.
Magnetization of (100) Cr/Fe/Cr and Pd/Fe/Pd structures
Authors: Chang Chin-An
Published: July 2002

(100) oriented Cr/Fe/Cr and Pd/Fe/Pd sandwich structures have been deposited on (100) Si using the epitaxially grown (100) Pd/Cu and (100) Cu, respectively, as the seed, in a vacuum of low 10−7 Torr. Four structures each are compared, with a Fe thickness of 25, 50, 100, and 500 Å, keeping the Cr and Pd layers at 1000 Å. No reversal in anisotropy is observed between the in-plane and normal-to-plane magnetization over the entire Fe thickness range studied. The in-plane epitaxial relation determined among the metals allows a study of the magnetocrystalline anisotropy of Fe in these structures also. Both the Cr/Fe/Cr and Pd/Fe/Pd structures show an easier magnetization at low field along the [100] edge than the [110] one, with the Cr/Fe/Cr structures being more pronounced. Magnetizations along these two edges approach each other at higher field. These are the same as that of bulk Fe crystal. The possible lattice deformation of the Fe layers in these structures is also explored.
Sputter deposition of cobalt–palladium multilayers
Authors: Highmore R. J. , Shih W. C. , Somekh R. E. , Evetts J. E.
Published: July 2002

We have used ultrahigh vacuum dc magnetron sputtering to deposit cobalt–palladium multilayers on silicon substrates. The films have been characterized using vibrating-sample magnetometry, x-ray diffraction, and cross-sectional transmission electron microscopy. We have observed ways in which the films’ microstructures and magnetic properties vary as the sputtering pressure is altered, and related the changes in magnetic properties to the changes in microstructure.
Energy distribution measurements in radio frequency plasma discharges using a cubical analyzer
Authors: Nguyen Phi Long , Turkot R. B. , Ruzic D. N.
Published: July 2002

A compact and inexpensive cubical energy analyzer has been developed to measure ion and electron energy distributions at the boundaries of a rf plasma. It consists of two grids parallel to the plasma boundary behind which lies a 1 cm×1 cm×1 cm cube. The absorbed current and voltage on the grids and on each face of the cube can be monitored and biased independently. A Helmholtz coil on the outside of the cube allows a 0–15 G field to be produced perpendicular to the path through the gridded apertures. The advantages over standard gridded energy analyzers include direct measurements of ion-induced secondary electrons and separation of electrons, negative ions, and heavy and light mass positive ions to different collection surfaces. Measurements of the ion and electron energy distributions at the grounded electrode of a parallel plate 13.56 MHz plasma discharges clearly show a time-varying rf sheath and a non-Maxwellian electron energy distribution. Data is presented for Ar, CH4, and H2 plasmas.
The effect of radio frequency substrate biasing in the deposition of diamond-like carbon films in an electron cyclotron resonance discharge
Authors: Pastel P. W. , Varhue W. J.
Published: July 2002

The density, optical band gap, and hydrogen content of diamond-like carbon films have been controllably varied by radio frequency (rf) substrate biasing in an electron cyclotron resonance (ECR) discharge of CH4 and CH4–H2. The density varied from 1.4 to 2.2 g/cm3, the optical band gap from 2.7 to 1.2 eV, and the atomic fraction of hydrogen from 50% to 5% as rf substrate bias increased. Optical emission spectroscopy was used to characterize the glow discharge and establish the conditions under which either deposition or etching could occur.
Migration of hydrogen through thin films of ZrO2 on Zr–Nb alloy
Authors: McIntyre N. S. , Davidson R. D. , Weisener C. G. , Good G. M. , Mount G. R. , Warr B. D. , Elmoselhi M.
Published: July 2002

The barrier properties of ZrO2 to inward migration of deuterium have been investigated with a view to understanding the hydriding mechanisms of a Zr-2.5% Nb alloy used in CANDU nuclear reactors fuel channels. Thin film oxide specimens, grown in steam to ∼1 μm thickness, have been heated to 350 °C and exposed to deuterium gas at pressures ranging from 6×10−3 Pa to 101 kPa (1 atm) and times from 10 to 810 min. Some irreversible uptake can be measured for all exposures using secondary ion mass spectrometry. At low exposures, the shape of the deuterium concentration profile is can be fitted to a Fickian relationship. During longer exposures, the rate of deuterium ingress is sharply curtailed, presumably due to passivated outer oxide surface. Reactions between D2O vapor and the thin film oxide in the 10−3 Pa pressure region and above show a sharply higher uptake of deuterium than in the equivalent pressure of D2 gas. This is ascribed to a more efficient decomposition of D2O on the ZrO2 surface compared to D2.
Influence of the deposition gas mixture on the structure and failure modes of diamondlike carbon films
Authors: Seth Jayshree , Padiyath Raghunath , Babu Suryadevara V.
Published: July 2002

Diamondlike carbon films have been deposited from binary mixtures of 1,3 butadiene and hydrogen or argon in a radio-frequency parallel plate plasma reactor. An infrared spectroscopic analysis revealed some of the effects of the diluents (hydrogen and argon) on the bonding characteristics of the deposited films. The film properties are a strong function of the deposition gas mixture. Hydrogen and argon both increase the diamondlike behavior. However, there is a trade-off between enhanced diamondlike characteristics and a tendency to delaminate or crack due to excessive stress and poor adhesion. The failure modes and stress relief forms have been imaged by the Nomarski interference contrast technique. Two new stress relief forms have been observed.
Laser-assisted chemical vapor deposition of InN on Si(100)
Authors: Bu Y. , Ma L. , Lin M. C.
Published: July 2002

Laser-assisted chemical vapor deposition of InN on Si(100) using HN3 and trimethyl indium (TMIn) with and without 308-nm photon excitation has been studied with x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and scanning electron microscopy (SEM). Without 308-nm excimer laser irradiation, no InN film was built on the surface under the present low-pressure conditions. When the photon beam was introduced, InN films with In:N atomic ratio of 1.0±0.1 and a thickness of more than 20 Å (the limit of the electron escaping depth for the In 3d x-ray photoelectrons) were formed at temperatures of 300–700 K. The He ii UP spectra taken from these InN films agree well with the result of a pseudopotential calculation for the InN valence band. Our XPS measurements indicate a three-dimensional (3D) island growth of InN on Si(100) at 700 K, which is confirmed by the SEM images. Although the SEM images taken from the same samples with 2000 × magnification showed very smooth InN films, InN islands of about 100 nm in diameter could be clearly observed with a magnification of ≥20 000×. In contrast, the InN film grown at 300 K showed valleys of uncovered substrate instead of InN islands. These uncovered substrate areas, corresponding to about 5% of the surface exposed to the probing x-ray radiation, probably result from incomplete decomposition of In–C bonds and poor diffusion kinetics at this temperature. Above 800 K, dissociation and desorption of In- and N- containing species occurred and thus no InN film was formed on the surface.
Influence of single atomic height steps on F2 reactions with Si(100)-2×1
Authors: Carter Lawrence E. , Carter Emily A.
Published: July 2002

We have investigated the effect of single atomic height steps on the reactivity of F2 molecules with a clean Si(100)-2×1 reconstructed surface via molecular dynamics simulations using an ab initio derived Stillinger–Weber-type potential. Of the three types of single atomic height steps thought to commonly exist on Si(100) surfaces, the presence of the lower energy SA and SB rebonded steps had a negligible effect on reactivity compared to the perfect (100) surface while the higher energy SB′ nonbonded step slightly increased the adsorption probability. These results suggest that current discrepancies between experimental observations and theoretical predictions of the partitioning between reaction channels for F2 reacting with the Si(100) surface are not due to the presence of steps on the silicon surface in the laboratory.
Plasma-enhanced chemical vapor deposition of silicon, germanium, and tin nitride thin films from metalorganic precursors
Authors: Hoffman David M. , Prakash Rangarajan Sri , Athavale Satish D. , Economou Demetre J. , Liu Jia-Rui , Zheng Zongshuang , Chu Wei-Kan
Published: July 2002

Nearly stoichiometric silicon, germanium, and tin nitride thin films were deposited from the corresponding homoleptic dimethylamido complexes M (NMe2)4 (M=Si, Ge, Sn; Me=CH3), and an ammonia plasma at low substrate temperatures (<400 °C). Tin nitride films were also deposited from Sn (NMe2)4 and ammonia without plasma activation. The films showed little (<few at. %) or no carbon or oxygen contamination. The barrier properties of the silicon and germanium nitride films were evaluated by using backscattering spectrometry. Homoleptic dimethylamido silicon and germanium compounds are attractive alternatives to silane and germane for use in the plasma-enhanced chemical vapor deposition of nitride thin films.
Plasma deposition of low-stress electret films for electroacoustic and solar cell applications
Authors: Klemberg-Sapieha J. E. , Martinu L. , Wertheimer M. R. , Günther P. , Schellin R. , Thielemann C. , Sessler G. M.
Published: July 2002

We studied electric charge retention and internal stress in low-pressure plasma-deposited silicon-compound films (silicon nitride, oxide, and oxynitrides), prepared from SiH4/NH3/N2O mixtures in a dual-mode microwave/radio frequency (2.45 GHz/13.56 MHz) plasma at low (∼30 °C) substrate temperature. The internal stress is found to vary from tensile (∼+150 MPa) to compressive (∼−100 to −500 MPa) when the bombarding ion energy is increased. Minimum stress values occur for the substrate bias voltage of about −100 V, which also results in a high charge stability on the film surface. Further improvement of the electret properties is achieved by postdeposition annealing, by exposure to organosilicone vapors, and by using oxynitride layers. This is confirmed by the presence of deeper charge traps, as determined by the measurement of thermally stimulated discharge currents, and by chemical stabilization of the film surfaces, as revealed by x-ray photoelectron spectroscopy. The films are considered for novel miniaturized electret microphones and electret-enhanced solar cells.
Nanotribology on a polymer network film
Authors: Haugstad G. , Gladfelter W. L. , Jones R. R.
Published: July 2002

Scanning force microscopy (SFM) of topography, frictional force, and stiffness on thin gelatin films reveals an entire spectrum of tribological behavior. Images display two distinct phases of gelatin whose characteristics relate to the degree of crystallinity. Dissimilar regimes of velocity- and load-dependent friction and wear on each phase indicate glassy, rubbery, or melt behavior. Of fundamental importance is the finding that energy transferred to the film in the vicinity of the sliding SFM microasperity modifies film response. Moderate frictional heating melts the highly crystalline phase, but reversibly induces rubbery behavior on the partially amorphous phase. More extreme frictional heating melts the latter and allows the liberated molecules to reassociate irreversibly into the highly crystalline phase. This relatively slow process (minutes) is imaged in real time on the submicron scale. Relaxation from rubbery to glassy behavior upon termination of perturbative scanning is extremely slow (hours) and also is characterized in frictional images. However, in this case the imaging process itself hastens the relaxation, apparently by providing energy to activate some relaxational processes.
Studies of reactive sputtering of multi-phase chromium nitride
Authors: Nyberg T. , Skytt P. , Gålnander B. , Nender C. , Nordgren J. , Berg S.
Published: July 2002

We have presented a model for reactive sputter deposition of two-phase materials. This model has been applied to reactive sputtering of chromium nitride where it is assumed that either Cr2N or CrN is formed. In order to test the validity of the model, a number of deposition experiments has been performed where the film composition for different reactive gas supplies has been estimated by means of in situ soft x-ray emission spectroscopy. The results have been compared with predicted film compositions according to the model and the experimental findings agree qualitatively with the simulations.
Analytic representations of the dielectric functions of crystalline and amorphous Si and crystalline Ge for very large scale integrated device and structural modeling
Authors: Leng J. , Opsal J. , Chu H. , Senko M. , Aspnes D. E.
Published: July 2002

Various representations of the dielectric functions of semiconducting materials have been proposed. We compare five different models for representing the dielectric functions of crystalline (c-) Si, amorphous (a-) Si, and c-Ge from 1.5 to 6.0 eV. The four-oscillator critical point with parity plus one-dimensional tight-binding model (CPP-1D) best represents c-Si. Different models best represent a-Si and c-Ge. These representations provided a basis for modeling variations encountered in semiconductor manufacturing.
Enhanced secondary electron yield from oxidized regions on amorphous carbon films studied by x-ray spectromicroscopy
Authors: Díaz Javier , Anders Simone , Cossy-Favre Aline , Samant Mahesh , Stöhr Joachim
Published: July 2002

Photoemission electron spectromicroscopy with synchrotron radiation has been used to study the correlation between the chemical surface composition and secondary electron yield from the surface of amorphous carbon films. Regions of about 4 μm diam were found which exhibited up to ten times higher secondary electron emission than the rest of the film. Near edge x-ray absorption fine structure spectroscopy of these regions showed that they contained highly oxidized carbon in the form of carboxylic and carbonate groups. These observations might be linked to the field emission properties of these films.
Stress, microstructure, and stability of Mo/Si, W/Si, and Mo/C multilayer films
Authors: Windt David L.
Published: July 2002

The stresses in periodic Mo/Si, W/Si, and Mo/C multilayer films were determined from wafer-curvature measurements. The layer thickness of each material was varied systematically, and parametric stress contours were generated, showing contours of constant stress in the two-dimensional layer thickness parameter space. These results illustrate that the net stress in a periodic multilayer is not an intrinsic property of the film (for specific deposition conditions) but, rather, depends strongly on the individual layer thicknesses. X-ray diffraction measurements show (a) how the lattice spacing in the W and Mo crystallites varies with layer thickness, and (b) in the case of the W/Si films, how the phase composition of the polycrystalline W layers vary with W layer thickness. In the case of the W/Si and Mo/Si multilayers, irreversible stress changes were observed after the samples were stored in air at room temperature for a period of several months. Stress–temperature measurements made on the as-deposited W/Si and Mo/Si samples also reveal irreversible stress changes (both positive and negative, depending on the layer thicknesses) after thermal cycling to 300 °C; x-ray diffraction measurements were used to identify any associated changes in the W and Mo microstructure. We describe mechanisms that can explain the observed stress behavior, and also discuss the significance of these results, particularly with regard to the use of these films for high-performance multilayer x-ray optics.
Compositional heterogeneity in ceria-based mixed oxides observed by x-ray photoelectron spectroscopy
Authors: Graham G. W. , Roe C. L. , Haack L. P. , Straccia A. M.
Published: July 2002

It is argued that compositional heterogeneity in certain reducible mixed oxides, like Ce1−xZrxO2, can be inferred from a variation in the metals ratio, as measured by x-ray photoelectron spectroscopy, between fully oxidized and partially reduced states of the oxide, provided that the characteristic linear dimension of the heterogeneity is at least as large as the typical electron inelastic mean-free path. The argument is supported by experimental results from two examples involving mixed phases, one in which the length scale is 100 nm and the other in which the domains are too small for detection by standard x-ray diffraction.
Manganese and germanium redistribution in In0.53Ga0.47 As grown by molecular beam epitaxy
Authors: Silberg E. , Chang T. Y. , Caridi E. A. , Evans C. A. , Hitzman C. J.
Published: July 2002

The redistribution of Mn in MBE grown In0.53Ga0.47 As layers containing different combinations of Mn and Ge doping pulses and subjected to various annealing conditions has been studied by secondary ion mass spectrometry (SIMS). The results indicate that Ge has a negligible diffusivity for temperatures up to 700 °C while the diffusion coefficient of Mn is approximately inversely proportional to the local Mn concentration. Accumulation of Mn in amounts proportional to the local Ge concentration has also been observed, suggesting the formation of donor–acceptor pairs with a certain fraction of Ge in the crystal. For those Mn atoms not immobilized by pairing, the diffusion coefficient is found to be reduced by nearly two orders of magnitude by the presence of Ge in the layer with very little dependence on the spatial distribution of Ge.
Abrupt transitions in composition and doping profile in GaAs–Ga1−xAlxAs heterostructures by atmospheric pressure MOVPE
Authors: Maluenda J. , Frijlink P. M.
Published: July 2002

Ga1−xAlx As–GaAs quantum wells are grown by atmospheric pressure MOVPE. Wells as narrow as 25 Å are made. Interface quality in relation to alloy clustering and abruptness in change of Al content is characterized with the aid of luminescence spectrum measurements. A remarkable agreement is found between the experimental n=1 electron to heavy hole transition energies and those which are calculated with the simple rectangular well model. The results indicate that the Al content changes at the interfaces over less than one unit cell. Single and multiple period modulation-doped GaAs–Ga1−xAlxAs heterostructures have been grown. Single period structures exhibit electron mobilities of 6700, 80 000, and 90 000 cm2 V−1s−1 at 300, 77, and 4 K for sheet carrier concentrations of 7.4×1011, 8.3×1011, and 3.9×1011 cm−2, respectively. To our knowledge, these values represent the best mobilities reported in this structure grown by atmospheric pressure MOVPE. Preliminary results on field effect transistors show a threefold increase of transconductance as temperature decreases from ambient to 77 K. Furthermore, we report mobility enhancement in ‘‘inverted’’ structures in which the conducting accumulation layers are located at the interfaces formed by growth of GaAs on top of (Ga,Al)As.
Structure of the Al–GaP(110) and Al–InP(110) interfaces
Authors: Kahn A. , Bonapace C. R. , Duke C. B. , Paton A.
Published: July 2002

The Al–GaP(110) and Al–InP(110) interfaces are characterized with low energy electron diffraction and Auger electron spectroscopy. Both interfaces are reactive, i.e., the replacement of the cation by Al is thermodynamically favorable. However, Al evaporated on the room temperature substrates has a high surface mobility and forms metallic islands which leave the atomic structure of the uncovered semiconductor areas unperturbed. Limited Al–substrate reaction can be detected at room temperature. Moderate annealing triggers a large scale Al-cation replacement reaction and leads to the formation of AlP layers. The crystalline quality of the AlP layers is good for Al on GaP (0.01% lattice mismatch between AlP and InP) and poor for Al on InP (7% lattice mismatch between AlP and InP). The atomic geometry of AlP(110) is analyzed with multiple scattering LEED computation. A best fit structure is obtained which is consistent with the correlation recently obtained between atomic structure and atomic size on (110) semiconductor compound surfaces.
Room temperature exchange reaction at the Al–InP(110) interface: Soft x-ray photoemission studies
Authors: Kendelewicz T. , Petro W. G. , Babalola I. A. , Silberman J. A. , Lindau I. , Spicer W. E.
Published: July 2002

A room temperature exchange reaction between an Al adsorbate and In atoms from the InP(110) surface has been observed during the early stages (∼0.5 to 5 Å) of interface formation by means of soft x-ray photoemission spectroscopy of the Al 2p and In 4d core levels. As much as 8 Å of deposited Al was found to be required to slow down the transport of Al metal to the front of the reaction to the extent that an overlayer of nonreacted Al metal began to be observed on the surface. For all stages of barrier formation a segregation of In atoms, monitored by the chemical shift of the In 4d core lines, has been observed. A moderate heating (up to 200 °C) of a 12 Å deposition extends the exchange reaction deeper into the bulk. These results are discussed in the context of the widely studied Al–GaAs interface.
Tunneling and propagating transport in GaAs–Ga1−xAlxAs–GaAs(100) double heterojunctions
Authors: Mailhiot C. , McGill T. C. , Schulman J. N.
Published: July 2002

We present a study of the transport characteristics of electrons through abrupt GaAs–Ga1−xAlxAs–GaAs(100) double heterojunctions. The theoretical apparatus uses complex-k-band structures in the tight-binding approximation and transfer matrices. States on each side of the Ga1−xAlxAs central barrier are expanded in terms of a complex-k-bulk state basis so as to provide a description of the wave function at the GaAs–Ga1−xAlxAs(100) interface. We treat the case where the incoming state in GaAs is derived from near the conduction band Γ point. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating depending on the nature of the Bloch states available for strong coupling in the alloy. States derived from the same extremum of the conduction band appear to couple strongly to each other across the GaAs–Ga1−xAlxAs interface. Transport characteristics of incoming states derived from near the conduction band Γ point are examined as a function of the energy of the incoming state, thickness of the Ga1−xAlxAs barrier, and alloy composition x. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating, depending on the nature of the Bloch states available for strong coupling in the alloy.
Photoelectrochemical passivation of GaAs surfaces
Authors: Woodall J. M. , Oelhafen P. , Jackson T. N. , Freeouf J. L. , Pettit G. D.
Published: July 2002

A wet chemical technique is described for passivating air-exposed GaAs surfaces. The passivating layer is elemental arsenic which forms as a result of illuminating an n-type GaAs wafer immersed in a mixture of HCl acid and deionized 18 MΩ water with light from a mercury vapor lamp at intensities of 0.01–0.05 W-cm−2. Studies using XPS, LEED, and UPS show that the passivated surfaces have the following properties: (1) there is little or no Ga or Ga and As oxide species in the As film or at the film/GaAs interface; (2) a strong GaAs LEED pattern is observed after a 290 °C anneal following low energy ion beam bombardment. This suggests that the As/GaAs interface formed by photoetching is free of contaminates and that the GaAs surface is well ordered prior to ion bombardment or heat treatment. Thus, clean, well ordered surface of GaAs which have been previously air exposed can now be obtained at lower temperatures than previously. This creates new possibilities for surface studies, epitaxy, and metallization.
Ammonium fluoride deposition during plasma etching of silicon nitride
Authors: Brewer J. A. , Miller G. W.
Published: July 2002

During oxygen and carbon tetrafluoride plasma etching of silicon nitride, a light blue and water soluble film is deposited upon the surface of the silicon nitride layer. Depending upon the thickness, this film retards or completely inhibits the desired etching process. This film has been identified by infrared spectrophotometry as ammonium fluoride. The thickness of the ammonium fluoride layer has been determined to be a function of the ammonia to dichlorosilane mole ratio of the gas flow into the LPCVD reactor during deposition. For mole ratios greater then 4.0, the ammonium fluoride film thickness was observed to decrease to approximately one-third of the observed value at a mole ratio of 3.0. A possible mechanism for the formation of the ammonium fluoride layer is the reaction of ammonia molecules and hydrogen atoms (which have been occluded in the silicon nitride layer during deposition) with fluorine atoms from the plasma etching process. Increasing the mole ratio during deposition improves the stoichiometry of the silicon nitride layer and reduces the number of hydrogen atoms available for subsequent formation of ammonium fluoride during etching. The etching variations caused by ammonium fluoride deposition during plasma etching of silicon nitride can be minimized by optimizing the ammonia to dichlorosilane mole ratio during the deposition of the silicon nitride layer.
Electrical characterization of the GaAs/AlxGa1−xAs interface by conductance DLTS
Authors: Maracas G. N. , Laidig W. D. , Wittmann H. R.
Published: July 2002

Experimental data taken from MBE-grown GaAs/Al0.25 Ga0.75 As modulation doped structures are presented. Interface states are observed using backside modulated conductance deep level transient spectroscopy. This technique allows evaluation of states within the 2DEG as well as on either side of the interface. Energies of the subbands, Si donors in the AlGaAs, and the amount of band bending have been determined. The measurements agree closely with calculations of band energies in a triangular well with an interface electric field of ∼9×106 V/m.
Interactions in metallization systems for integrated circuits
Authors: Murarka S. P.
Published: July 2002

Conductive films are required to provide interconnection between contacts on the devices and between devices and outside world. Aluminum has been the most popular metal. Conducting polycrystalline silicon (polysilicon) film has been the conductor for gate and interconnection. PtSi has been used as a Schottky barrier contact and also simply as a contact for deep junctions. Refractory silicides are now used as gate and interconnection metallizations. Titanium/palladium/gold or titanium/platinum/gold beam lead technology was successful in providing high reliability connection to the outside world. Several similar schemes have been suggested or used in the integrated circuits. A considerable amount of work is carried out in adopting such a metallization scheme in integrated circuits. These include a study of metallurgical and chemical interactions between various materials and effect of such interactions on the properties of the materials and devices. In this paper a review of these studies will be presented.
Sputtering of refractory metal silicides from composite cathodes used in the Varian 3180/3190 sputtering system
Authors: Nichols Dennis R.
Published: July 2002

The techniques and procedures utilized to sputter the silicides of Mo, Ta, and Ti in a Varian 3180/3190TM system1 are presented. The electrical resistivity of a thin film is a sensitive indicator of film purity and/or uniformity.2,3 The affect of various system parameters on film resistivity is also presented. Variable parameters investigated included argon pressure, cathode power, sputtering rate, wafer temperature, and wafer bias.
Thin solid films to combat friction, wear, and corrosion
Authors: Hintermann H. E.
Published: July 2002

This paper deals with the relations and interactions of the substrate, the interface, and the functional hard overlay or diffusion coating deposited by chemical or physical vapor deposition, CVD or PVD, respectively, and how these structures influence the overall mechanical and physicochemical properties of the composite. Emphasis is given to the friction and wear behavior of the refractory carbides, nitrides, borides, and oxides, with and without lubrication, to the characterization of the mechanical strength of the interface as measured by the scratch test and thus, of the adhesion and cohesion properties, and to the corrosion behavior, mainly of TiC.
High-power sputter deposition of tantalum silicide films from a composite target
Authors: Sridhar C. G. , Chow R. , Powell R. A. , Stellrecht D. E.
Published: July 2002

Thin films of tantalum silicide were sputter deposited from a cold-pressed, vacuum-sintered target in a Varian 3180 system onto Si(100) wafers. Currently, the deposition of tantalum silicide from cold-pressed, vacuum-sintered targets is performed at relatively low powers of about 1 kW. Although the use of higher deposition power is of great practical interest to obtain increased deposition rates and wafer throughput, the effect on film properties must be determined. In this paper, films deposited at powers as high as ∼3 kW were characterized. The films were annealed in a Varian IA-200 rapid isothermal annealer. In many cases, analytical measurements such as stoichiometry, stress, microstructure, and morphology were performed before and after annealing. Small variations of film properties were observed when the deposition was done on a heated substrate or on a substrate with negative dc bias voltage applied. It will be shown here that low-resistivity (60–70 μΩ cm) film of tantalum silicide can be deposited from a cold-pressed, vacuum-sintered target at much higher than usual deposition power without affecting the film characteristics significantly.
Properties and structure of coevaporated NbSi2
Authors: Guoying Wu , Guobing Zhang , Yuan Wang Yang , Wei Xu , Hong Li Yong , Hopkins C. G. , Strathman M. D.
Published: July 2002

This paper will investigate the properties and structure of coevaporated NbSi2 under a variety of annealing times and temperatures. Data from transmission electron microscopy (TEM) in situ vacuum annealing, conventional furnace annealing, and infrared rapid thermal annealing will be presented. The temperatures in this study ranged from room temperature to 950 °C for these annealing techniques. The results obtained in this work will be contrasted to those obtained for other interconnect materials such as polysilicon and refractory metal silicides.
Application of the self-aligned titanium silicide process to very large-scale integrated n-metal-oxide-semiconductor and complementary metal-oxide-semiconductor technologies
Authors: Haken Roger A.
Published: July 2002

This paper reviews recent progress towards integrating the self-aligned titanium silicide process into VLSI NMOS and CMOS technologies, to simultaneously reduce the gate and junction sheet resistances to below 1 Ω/sq. In addition to reviewing the base line self-aligned TiSi2 process, the key issues that must be addressed if the process is going to be successfully integrated into a VLSI process flow, without having adverse effects on device parameters, will be discussed. Such issues are how the sheet resistance can be reduced to <1 Ω/sq without bridging between the gate and source/drain regions, the effect of silicide stress on gate oxide integrity, and how both P- and N-type junctions can be silicided without adversely affecting diode or transistor properties. Recent results on the hot electron hardness of silicided devices compared to unsilicided transistors will also be presented. The implementation of the self-aligned titanium silicide process using rapid thermal processing to simultaneously fabricate transistor gates and junctions with a sheet resistance of 1 Ω/sq will also be described. Using the self-aligned TiSi2 technology, fully functional VLSI CMOS and NMOS circuits of the 64K static random access memory class of complexity, with 1 μm gates, have been fabricated with yield that is similar to unsilicided parts.
Technique for measuring surface diffusion by laser-beam-localized surface photochemistry
Authors: Zeiger H. J. , Tsao J. Y. , Ehrlich D. J.
Published: July 2002

A technique is described for determining the surface diffusivity of a weakly bound adsorbate by measuring the kinetics of a spatially localized, laser-beam-driven surface photoreaction. The diffusivity is extracted from the experimental data by means of a Green’s function integral technique. The solution is numerically integrated in order to calculate the spatial and temporal evolution of the surface-number-density of parent and product molecules. The new technique has been applied to experiments with tetraethyl lead molecules adsorbed on sapphire.
The influence of oxidation and annealing on InP native chemical oxides
Authors: Korotchenkov G. S. , Mikhailov V. A. , Tsvitsinsky V. I.
Published: July 2002

Chemical oxidation of InP (100) was carried out in hot nitric acid. Composition of the oxides was determined by means of Auger electron spectroscopy employing layer by layer etching with Ar+ ions. It is shown that the composition of the chemical oxide is similar to that of anodic oxides. They are characterized by substantial compositional nonuniformity, that increases with increase of oxide thickness and decreases with annealing temperature. Annealing at T=280–400 °C results in improved compositional uniformity and a higher concentration of oxidized phosphorus in the oxide. Annealing at such temperatures, especially at T≥400 °C, is accompanied by broadening of the interface between the oxide and InP and a substantial concentration of unoxidized phosphorus near the interface. The interfacial broadening and concentration of unoxidized phosphorus are considered to be the result of reaction between P-oxide and InP.
Schottky barriers on atomically clean n-InP (110)
Authors: Kendelewicz T. , Newman N. , List R. S. , Lindau I. , Spicer W. E.
Published: July 2002

We report the results of a systematic study of the Schottky barrier heights on n-type InP (110). The measurements were performed on thick diodes and thin metal overlayers grown at room temperature under ultrahigh vacuum conditions on cleaved surfaces. A large number of metals, ranging from strongly reactive Ni, Al, Cr, Mn, and Pd to less reactive or nonreactive Ag, Au, Cu, Ga, and Sn have been used to correlate the barrier height with the interfacial chemistry. The barrier heights have been determined using the current-voltage characteristics of diodes and the band bending related shifts in the core level spectra for the thin overlayers. Soft x-ray photoemission spectroscopy has also been used to characterize the chemical reactions on a microscopic scale during the initial stages of the interface formation. Our results show several notable exceptions from the systematics relating the barrier heights with the interfacial chemistry. These results provide a critical test of currently considered models of Schottky barrier formation.
Anisotropic reactive ion etching technique of GaAs and AlGaAs materials for integrated optical device fabrication
Authors: Yamada Hirohito , Ito Hiromasa , Inaba Humio
Published: July 2002

This paper reports a reactive ion etching (RIE) technique using a Cl2–Ar gas mixture for anisotropic microprocessing of GaAs and AlGaAs materials and its fundamental characteristics aimed to applications to monolithic integration of optical devices. This technique allows one to realize very fine as well as deep processing perpendicular to the wafer surface with smooth side walls, independent of the crystallographic orientation of these semiconductor materials. The etching rate was found to be controllable over a wide range by suitably adjusting the gas composition and the total gas pressure in this gas mixture. We experimentally obtained the optimum condition for smooth and perpendicular etching for both the materials at the total gas pressure of 2 Pa (1.5×10−2 Torr) with the gas flow ratio of Cl2 : Ar=1 : 5. Under this condition the etching rate ratio of GaAs to SiO2 was demonstrated more than 70. The surface damage introduced by this RIE was confirmed to be comparable at least to the case of the wet chemical etching through the measurement of photoluminescence intensities from GaAs samples.