bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of hydrogen annealing on second-harmonic generation from SiO2/Si(111) interfaces
Authors: Hirayama Hiroyuki , Ito Fuminori , Watanabe Kohji
Published: July 2002

We studied the effect of hydrogen annealing on second-harmonic generation (SHG) from thermally grown SiO2/Si(111) interfaces. With s-polarized yttrium aluminum garnet (YAG) fundamental beam (1064 nm) excitation, p-polarized SHG showed a threefold symmetric intensity pattern in which weak and strong peaks appear alternately every 60°. After hydrogen annealing, the intensity of the strong peaks became weaker. This is mainly due to reduction of the nonlinear susceptibility tensor component χzxx. Because hydrogen annealing terminates dangling bonds at the interface, this result means that SHG is sensitive to interface disorder including dangling bonds. However, χzxx was not completely eliminated by hydrogen annealing. By comparing SHG from hydrogen-annealed thermal oxide and native oxide/Si(111) interfaces, we attribute the residual χzxx to interface bond stress.
Preparation and characterization of anisotropic chain structures in polyimide films
Authors: Wu Hai-Ming , Zhu Yang-Ming , Luo Qi , Yang Xiao-Ming , Lu Zu-Hong , Wei Yu
Published: July 2002

Polyimide (PI) films were prepared by the pulsed laser ablation, the rubbing of PI-coated substrates, the transfer of PI monolayers by vertical dipping method and the horizontal deposition of flowing water supported PI monolayers, and investigated by atomic force microscopy. A macroscopic anisotropy was measured in all these films. However, we found PI chain molecules were not uniformly oriented on a microscopic scale in the films prepared by the pulsed laser ablation and rubbing methods while a relatively perfect local and global orientation of PI chains existed in PI monolayer films.
Auger electron spectroscopy and x-ray photoelectron spectroscopy studies of adhesion failure of Ni/Au-plated contacts in ceramic electronic packages
Authors: Braski D. N. , Winters E. D.
Published: July 2002

Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) were used to study a problem of poor adhesion of plated Ni/Au contact layers in ceramic electronic packages. XPS surveys showed that the Ni/Au films failed at the Mo contact pad/Ni interface. When the films were stripped, in situ, AES revealed a contamination layer of carbonaceous material on both the contact pad and mating surface of the stripped film. The XPS C 1s peak obtained from the ≊20-nm-thick carbonaceous contamination layer on a freshly exposed pad surface matched that for the same peak taken from a special mounting wax used in a process step prior to plating. The surfaces of both the contamination and the wax exhibited a characteristic disappearance of the C=O band after ≊1 min of Ar-ion sputtering. Plating adhesion was restored after the cleaning solutions used prior to plating were changed more frequently to prevent wax buildup.
Quantitative surface composition analysis using very high intensity nonresonant multiphoton ionization
Authors: He Chun , Basler Julian , Paul Anumita , Becker Christopher H.
Published: July 2002

The subject of this article is quantitative surface and material analysis under high sensitivity conditions. Various gases and one solid sample were studied, using high intensity (1014–1015 W/cm2), nonresonant multiphoton postionization in tandem with time-of-flight mass spectrometry. These atomic and molecular gases (Ar, Kr, NO, Xe, N2 and O2) possess high ionization potentials, requiring high photon flux density for ionization saturation. The solid sample SiO2, studied using 5 keV Ar+ sputtering, places a stringent test on quantitative analysis. Si and O have exceedingly different ionization potentials that require four and six photons for ionization, respectively. The experimental results demonstrate that it is possible not only to saturate species with high ionization potentials, but also to perform quantitative analysis by establishing a well-defined ionization volume for all species evolved from the surface.
In situ boron doping of Si and Si1−xGex epitaxial layers by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition
Authors: Park Jin-Won , Hwang Ki-Hyun , Joo Sung-Jae , Yoon Euijoon , Hwang Seok-Hee , Whang Ki-Woong
Published: July 2002

We report on the growth of in situ boron doped Si and Si1−xGex epitaxial layers at 510 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition. Boron concentration increases with B2H6 partial pressure. The boron concentration decreases as microwave power increases in Si epilayers and as Ge fraction increases in Si1−xGex epilayers. Enhanced ion bombardment at these conditions promotes the desorption of boron hydride in the growth surface. No growth rate change is observed in the Si epilayer with B2H6 partial pressure. However, a significant growth rate decrease is observed for the Si1−xGex epilayer with B2H6 partial pressure.
Failure mechanisms of anodized aluminum parts used in chemical vapor deposition chambers
Authors: Ponnekanti Srihari , Murugesh Laxman , Hanson Eric
Published: July 2002

Anodized aluminum parts used in chemical vapor deposition (CVD) reactor chambers for TEOS (tetra ethyl ortho silicate), passivation, and tungsten process clean chemistries were analyzed using scanning electron microscopy and energy-dispersive spectroscopy x-ray maps. Examination reveals that the primary cause of failure for all anodized Al parts is the same while individual mechanisms vary depending on the process chemistry used. The fundamental reason for failure of anodized aluminum part in CVD reactors is the formation and growth of aluminum fluoride below the anodized film at point defect sites. These point defect sites are imperfections in the anodized layer caused by precipitate particles such as Fe and Si, voids, sharp corners, and cracks due to differential expansion. In the 6061 alloy, the point defect sites act as high energy sites for the plasma fluorine attack. However, such defect sites can be capped off by the formation of a layer of MgF2 below the anodized film. The formation of MgF2 is dependent upon the availability of elemental Mg to diffuse to these point defect sites and also the number of defect sites. Some of the Mg is typically tied up with precipitates like Fe and Si. When free Mg is unavailable to form a barrier layer, subsequent fluorination of the substrate causes formation of AlF3. This results in stresses in the anodized layer that can ultimately lead to delamination of the anodized layer and failure of the part. The 1100 alloy does not contain Mg and thus fluorination results in the direct formation of AlF3 at point defect sites with no protective MgF2 layer present. An enhanced performance of anodized Al parts can be achieved by using pure aluminum alloys with controlled quantities of Mg to form the MgF2 barrier layer.
Three-dimensional equipment modeling for chemical vapor deposition
Authors: Werner Christoph , Ilg Matthias , Uram Kevin
Published: July 2002

Three-dimensional (3D) numerical equipment modeling using the simulator PHOENICS-CVD was used to investigate a low pressure chemical vapor deposition process for boron and phosphorus doped silicon glass deposition from TEOS, PH3, O2, and TEB gas sources. The simulation allows the 3D visualization of gas flow, temperature, and chemical concentration profiles in the reactor, as well as the calculation of the deposition rate as a function of position. Mixing of gases from different inlets and deposition uniformity due to reactive gas depletion were studied as a function of pressure, gas flow velocity, and reactor geometry. Comparison with experimental deposition rate data shows that published chemical models can well describe the undoped deposition, while additional chemical reactions seem to become important when PH3 is introduced in the reactor for phosphorus doped glass deposition.
Evidence for a surface optical phonon mode on NaCl(001)
Authors: Benedek G. , Glebov A. , Silvestri W. , Skofronick J. G.
Published: July 2002

High-resolution inelastic He atom scattering experiments have been used to measure the transverse optical mode on an in situ cleaved NaCl(100) crystal surface at a crystal temperature of 100 K in the 〈110〉 direction. The bound states of NaCl(001) lead to many resonance features in the time-of-flight spectra which act to obscure the desired surface phonon information. However, since the bound state energies are known, the resonance features are identified and removed. A slab calculation using the breathing shell model and surface perturbations which fulfill translational and rotational invariance conditions are used to interpret the measured surface phonons.
Vibrational spectra of oxygen on LaB6(100), (110), and (111) surfaces: A comparative study using high resolution electron energy loss spectroscopy
Authors: Rokuta E. , Yamamoto N. , Hasegawa Y. , Nagao T. , Trenary M. , Oshima C. , Otani S.
Published: July 2002

The vibrational properties of the (100), (110), and (111) surfaces of LaB6 with adsorbed oxygen are compared using high resolution electron energy loss spectroscopy (HREELS). Each surface offers a distinctly different set of possible adsorption sites and at room temperature the adsorption of oxygen yields a distinctly different HREELS spectrum. However, annealing the oxygen covered surfaces to 700 °C produces strikingly similar results, indicating a common oxygen induced structure for the three surfaces.
Surface-immobilized plasma proteins and platelet activation in the non-self- recognition of foreign materials
Authors: Nygren Håkan , Tengvall Pentti , Lundström Ingemar
Published: July 2002

The immobilization of plasma proteins and activation of platelets were studied at surfaces of five different materials, i.e., titanium, gold, quartz, methylized quartz, and mercaptopropanediol monolayers on gold. Immobilization of plasma proteins was measured with ellipsometry using specific antibodies for detection of individual proteins adsorbed after exposure of materials to heparin plasma for 1 min. Activation of platelets was measured with immunofluorescence of platelet surface antigens and F-actin after exposure of materials to whole blood from 15 s to 4 min. The results show different profiles of surface-immobilized plasma proteins and differences between the material surfaces in the number of adhering cells, the degree of aggregation of the cells, the content of F-actin, and the number of extracellular microparticles adhering to the surface. Blood–titanium contact resulted in a characteristic, early and marked formation of F-actin in platelets.
Electronic structure of cubic gallium nitride films grown on GaAs
Authors: Ding S. A. , Neuhold G. , Weaver J. H. , Häberle P. , Horn K. , Brandt O. , Yang H. , Ploog K.
Published: July 2002

The composition, surface structure, and electronic structure of zinc blende–GaN films grown on GaAs (100) and (110) by plasma-assisted molecular beam epitaxy were investigated by means of core and valence level photoemission. Angle-resolved photoelectron spectra (photon energy 30–110 eV) exhibited emission from the Ga 3d and N 2s levels, as well as a clear peak structure in the valence band region. These peaks were found to shift with photon energy, indicative of direct transitions between occupied and unoccupied GaN bands. By using a free electron final band, we are able to derive the course of the bands along the Γ-X and Γ-K-X directions of the Brillouin zone and to determine the energy of critical points at the X point. The relative energies of the Ga 3d and nitrogen 2s bands were also studied, and a small amount of dispersion was detected in the latter. The resulting band structure is discussed in relation to existing band structure calculations.
Study of buried interfaces by soft x-ray fluorescence spectroscopy excited by synchrotron radiation
Authors: Ederer D. L. , Carlisle J. A. , Jimenez J. , Jia J. J. , Osborn K. , Callcott T. A. , Perera R. C. C. , Underwood J. H. , Terminello L. J. , Asfaw A. , Himpsel F. J.
Published: July 2002

This article is a summary of four different aspects of soft x-ray spectroscopy that are being used or developed by our group to probe the interface. The first is to study the change in valence band fluorescence emission by mimicking a high density of interface atoms through the use of a multilayer. The second method uses an intense localized excited state to characterize the buried interface. The third uses Raman scattering to probe changes in band structure produced by stoichiometric changes in the valence band density of states for atoms at the interface. Finally, a method to study interface atoms by using valence emission from interface atoms that are excited by x-ray standing waves is being developed.
Growth and characterization of silicon thin films employing supersonic jets
Authors: Pacheco K. A. , Ferguson B. A. , Mullins C. B.
Published: July 2002

Supersonic jets of Si2H6 have been employed to grow single crystalline silicon thin films on Si(100) and polysilicon surfaces at substrate temperatures of 500–650 °C. Films deposited on Si(100) employing high and low kinetic energy jets are epitaxial as determined by reflection high energy electron diffraction. The uniformity and growth of films deposited on polysilicon by high energy ∼2 eV (1% Si2H6 in hydrogen) and low energy ∼0.09 eV (pure Si2H6) Si2H6 jets are compared to silicon growth employing ultrahigh vacuum chemical vapor deposition (UHV-CVD). To ascertain the influence of high kinetic energy on the growth of silicon from disilane, the reaction probability is estimated from growth measurements for all techniques and compared. The high energy jet is found to have a substantially higher reaction probability compared to the low energy jet and UHV-CVD indicating that the growth is enhanced by the high energy disilane. The disilane flux distribution employing the high energy jet is sharply peaked along the centerline causing a peaked growth profile across the 4 in. wafer. The silicon growth profile obtained from the high energy jet broadens slightly as the substrate temperature decreases. The higher flux at the centerline results in a higher hydrogen coverage compared to the wafer edge which affects the reaction probability in the two locations relative to one another. As the substrate temperature decreases, the growth profile flattens since the lower hydrogen desorption rate, and resulting higher hydrogen coverage, reduces the disilane adsorption probability at the centerline more than at the wafer edge. The growth distribution from the high energy jet is found to become slightly less peaked when the carrier gas is changed from hydrogen to helium.
Fabrication and characterization of graded refractive index silicon oxynitride thin films
Authors: Callard S. , Gagnaire A. , Joseph J.
Published: July 2002

Oxynitride films with continuous variations of the optical index with thickness were grown by electron cyclotron resonance plasma-enhanced chemical vapor deposition using silane as a silicon precursor and oxygen and nitrogen as plasma gases. Specific linear and parabolic index profiles were fabricated by computerized-control gas flow. These gradient index layers were characterized by spectroscopic ellipsometry. The data reduction was performed by polynomial analysis. The validity of the ellipsometric results was also verified by performing an in-depth analysis via the chemical etching of the gradient index layers.
Particle contamination formation in magnetron sputtering processes
Authors: Selwyn Gary S. , Weiss Corey A. , Sequeda Federico , Huang Carrie
Published: July 2002

Defects caused by particulate contamination are an important concern in the fabrication of thin film products. Often, magnetron sputtering processes are used for this purpose. Particle contamination generated during thin film processing can be detected using laser light scattering, a powerful diagnostic technique which provides real-time, in situ imaging of particles >0.3 μm on the target, substrate, or in the plasma. Using this technique, we demonstrate that the mechanisms for particle generation, transport, and trapping during magnetron sputter deposition are different from the mechanisms reported in previously studied plasma etch processes, due to the inherent spatial nonuniformity of magnetically enhanced plasmas. During magnetron sputter deposition, one source of particle contamination is linked to portions of the sputtering target surface exposed to weaker plasma density. There, film redeposition induces filament or nodule growth. Sputter removal of these features is inhibited by the dependence of sputter yield on angle of incidence. These features enhance trapping of plasma particles, which then increases filament growth. Eventually the growths effectively “short-circuit” the sheath, causing high currents to flow through these features. This, in turn, causes mechanical failure of the growth resulting in fracture and ejection of the target contaminants into the plasma and onto the substrate. Evidence of this effect has been observed in semiconductor fabrication and storage disk manufacturing. Discovery of this mechanism in both technologies suggests it may be universal to many sputter processes.
In situ analysis of Si(100) surface damage induced by low-energy rare-gas ion bombardment using x-ray photoelectron spectroscopy
Authors: Ishii Masahiko , Hirose Yoshiharu , Sato Toshikazu , Ohwaki Takeshi , Taga Yasunori
Published: July 2002

The damage layer of a Si(100) surface induced by low-energy (300–600 eV) rare-gas (Ne, Ar, or Xe) ion bombardment was in situ analyzed by x-ray photoelectron spectroscopy (XPS). The XPS analysis showed that, irrespective of the ionic species, an amorphous Si (a-Si) layer with a thickness of 10–30 Å was formed and saturated by the dose of 1015 cm−2. It also showed that the thickness increased linearly with the ion energy and Ne ions formed the thickest a-Si layer. The saturated thickness measured with the XPS analysis has been confirmed by cross-sectional transmission electron microscopy. Formation process of the a-Si layer under small dose of ions can be explained in terms of the Poisson process. As a result, the size of an a-Si region formed by single ion bombardment was estimated. The region, which is supposed to have a cylindrical shape, has a radius of 2–4 Å and a height of 10–30 Å for each ionic species and energy. In situ XPS analysis for the Si surface bombarded with ion beams revealed the growth process of the a-Si layer in addition to the dependence of the thickness on the ionic species, energy, and dose.
Preparation of highly transparent and conducting Ga2O3–In2O3 films by direct current magnetron sputtering
Authors: Minami T. , Takeda Y. , Kakumu T. , Takata S. , Fukuda I.
Published: July 2002

Multicomponent Ga2O3–In2O3 films have been prepared by dc magnetron sputtering using targets with a Ga content [Ga/(In+Ga) atomic ratio] of 0–60 at. %. Transparent conducting thin films prepared with Ga contents up to about 40 at. % were identified as Ga-doped In2O3 (In2O3:Ga). A minimum resistivity of 5.8×10−4 Ω cm and a maximum carrier concentration of 5×1020 cm−3 were obtained in an In2O3:Ga film prepared at a substrate temperature of room temperature with a Ga content of 30 at. %. Transparent conducting thin films prepared with a Ga content of 45–50 at. % were identified as a ternary compound: gallium indium oxide, (Ga,In)2O3. The electrical properties exhibited by the (Ga,In)2O3 films were relatively independent of the substrate temperature from room temperature to 350 °C. A sheet resistance of 1–2 kΩ and an average transmittance above 95% were obtained in (Ga,In)2O3 films with a thickness of about 20 nm and prepared with a Ga content of 50 at. %.
Flexible fluorocarbon wire coatings by pulsed plasma enhanced chemical vapor deposition
Authors: Limb Scott J. , Gleason Karen K. , Edell David J. , Gleason Edward F.
Published: July 2002

A method to coat thin wires, 25 μm in diameter, with fluorocarbon material that is flexible and conformal has been achieved using pulsed plasma enhanced chemical vapor deposition (PECVD). This process enables the chemical composition of the films to be tailored in order to achieve similar stoichiometry and chemical composition to bulk polytetrafluoroethylene [PTFE, (CF2)n, Teflon™]. The deposited film had a F/C ratio of 1.9 and a CF2 fraction of 65%. In comparison, a film deposited under continuously applied power had a F/C ratio of only 1.6 and a CF2 fraction of 32% and was found to form brittle wire coatings. The flexibility of the pulsed PECVD film was consistent with its connectivity number of 2.1 corresponding to an underconstrained, flexible material. In addition, the connectivity number for the brittle film was 2.5, consistent with an overconstrained brittle network.
Tantalum metallization using an electron–cyclotron-resonance plasma source coupled with divided microwaves
Authors: Nishimura H. , Ono T. , Oda M. , Matsuo S.
Published: July 2002

Tantalum film deposition using an electron–cyclotron-resonance (ECR) plasma source coupled with divided microwaves has been investigated. In this technique, we can obtain high quality thin films because of the enhancement of the sputtering and film formation reaction achieved by highly ionized ECR plasma. Beta tantalum with high compressive stress and high resistivity (150 μΩ cm) was obtained by Ar plasma. By using Xe, however, α-Ta with a resistivity of 13 to 18 μΩ cm was obtained, at temperatures as low as 150 °C, by the moderate ion-bombardment effect of Xe. The compressive internal stress decreased with increasing temperature or film thickness. The stress change in air was less than 5 MPa for 0.6-μm-thick film even after 103 h exposure in air. Fine patterns with 0.12 μm width were etched into 0.4-μm-thick Ta by ECR etching. We can obtain low stress, low resistivity, and stable Ta films using ECR sputter deposition by controlling the ion bombardment effect. We demonstrated that ECR sputter deposition can be used for deposition of Ta film as absorbers of x-ray masks and as diffusion barriers in large scale integrated devices.
Real-time monitoring of scattered laser light by a single particle of several tens of nanometers in the etching chamber in relation to its status with the equipment
Authors: Uesugi Fumihiko , Ito Natsuko , Moriya Tsuyoshi , Doi Hiroshi , Sakamoto Shingo , Hayashi Yuji
Published: July 2002

In order to detect a single particle of several tens of nanometers and to clarify the relationship between particle outbreak and the workings of wafer processing equipment, a scattered laser light measurement system has been produced experimentally. The system is composed of a high frequency pulse-laser oscillator, a two-dimensional charge-coupled device image processor, and a status-signal processor connected to the wafer process equipment. By using this system, in situ monitoring of a single particle of several tens of nanometers that flakes off films deposited on the upper ground electrode of the plasma etching chamber, and observation of its trajectory are successfully demonstrated for real tungsten etchback processing. Moreover, data from the system show that, after processing several hundred wafers, the outbreak of particles in the etching chamber had a correlation with specific workings of the etching equipment, such as turning off the rf power and the injection of purge gas to the chamber. The scattered light measurement system has demonstrated its ability to monitor particle outbreak, transport, and behavior.
Properties of ZnO:In film prepared by sputtering of facing ZnO:In and Zn targets
Authors: Tominaga K. , Umezu N. , Mori I. , Ushiro T. , Moriga T. , Nakabayashi I.
Published: July 2002

ZnO:In films were prepared by a sputtering method with targets facing. The lowest resistivity film is obtained at a substrate temperature of 150 °C using a ZnO target doped with 3 wt % In2O3. At substrate temperatures above 300 °C the resistivity of the film increases as the carrier concentration decreases. This implies a significant decrease in the donor impurity, ascribed to evaporation of the indium during film growth. From experiments with an additional Zn supply during deposition, we found that all of the doped indium is ionized as donor in ZnO:In, and that evaporation of depositing indium atoms is enhanced above 250 °C.
Comparison of plasma chemistries for dry etching thin film electroluminescent display materials
Authors: Lee J. W. , Pathangey B. , Davidson M. R. , Holloway P. H. , Lambers E. S. , Davydov B. , Anderson T. J. , Pearton S. J.
Published: July 2002

Chlorine (Cl2 or BCl3, with additions of Ar or N2), fluorine (SF6/Ar) and methane/hydrogen (CH4/H2/Ar or CH4/H2/N2) based plasmas have been examined as a function of composition, source and sample chuck power, and pressure, for dry etching of the typical luminescent sulphide phosphors (ZnS, SrS), conductive electrode materials [indium tin oxide, (ITO) and TiW] and insulators (Al2O3, alumina/titania-ATO) used in thin film electroluminescent displays. It is necessary to have both a high ion flux and an ion energy above a particular threshold (typically ⩾125 eV) in order to achieve practical etch rates for the high bond strength materials such as Al2O3, alumina/titania and SrS. The fastest etch rates for ZnS, Al2O3 and aluminum tin oxide are obtained with Cl2/Ar for SrS with SF6/Ar and for ITO with CH4/H2/Ar.
Response surface study of inductively coupled plasma etching of GaAs/AlGaAs in BCl3/Cl2
Authors: Agarwala Sambhu , King Oliver , Horst Scott , Wilson Rick , Stone Dennis , Dagenais Mario , Chen Y. J.
Published: July 2002

A central composite design response surface study was used to determine the etching characteristics of GaAs/AlGaAs in high-density inductively coupled BCl3/Cl2-based plasmas as a function of process parameters including inductive power, substrate bias, and pressure. Equietch rates were obtained for GaAs and AlxGa1−xAs in the entire parameter space investigated and ranged from approximately 0.3 to 1.0 μm/min. The etch rate of GaAs/AlGaAs grew with an increase in all three parameters. Variations in inductive power had the maximum effect on the etch rate while the bias affected the etch rate the least. In contrast, bias played a significant role in the etch rate of photoresist indicating different mechanisms for resist etching. An ion energy threshold was observed for resist etching which was found to increase with decreasing inductive power. Anisotropic GaAs/AlGaAs etch profiles were obtained over a wide range of parameters including very low substrate bias. Extremely smooth etched surfaces were observed for most etch conditions.
Intelligent process control of indium tin oxide sputter deposition using optical emission spectroscopy
Authors: Eisgruber I. L. , Engel J. R. , Hollingsworth R. E. , Bhat P. K. , Wendt R.
Published: July 2002

The dc sputtering of indium tin oxide (ITO) is a high deposition rate process yielding a low-resistivity, high-transmission thin film that is useful to the display, photovoltaics, and optoelectronics industries. However, a number of deposition variables that are not typically controlled during sputtering, such as target age and history, and water partial pressure, can cause ITO film properties to deviate from their optimum values. Control of such deviations is necessary to maintain high yield and low costs in manufacturing. Optical emission spectroscopy (OES) can be used to monitor the deposition process and maintain optimum film properties. Basic relationships between the OES signals during deposition and the ITO film properties were established. Closed-loop control of the ITO deposition was implemented using OES. Improved yield—specifically, decreased resistivity, decreased variance in resistivity, and decreased variance in thickness—was demonstrated.
Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering
Authors: Wang Xin , Helmersson Ulf , Madsen Lynnette D. , Ivanov Ivan P. , Münger Peter , Rudner Staffan , Hjörvarsson B. , Sundgren Jan-Eric
Published: July 2002

Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O2 gas mixtures at substrate temperatures ranging from 650 to 850 °C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1Ti0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of ∼300 nm, the typical dielectric constants as measured at ∼77 K and 1 MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films.
Atomic force microscopy observation of human lymphoid cells chronically infected with the human immunodeficiency virus
Authors: Cricenti A. , Generosi R. , Girasole M. , Scarselli M. A. , Perfetti P. , Bach S. , Colizzi V.
Published: July 2002

The interaction between lymphocyte cell and human immunodeficiency virus (HIV) has been studied at membrane level by atomic force microscopy (AFM) in the repulsive regime of contact mode. Morphological characteristics of noninfected lymphoid cells and HIV infected cells were easily imaged from fixed and dried cell preparations. After HIV exposure we observed a decrease in surface protrusions (lost of microvilli) and the creation of many dips. Some particles, presumably of viral origin (120–130 nm size), were also observed in proximity of the cell surface. Similar changes have been observed by AFM on cells exposed to intense electromagnetic field thus indicating that such cells undergo modifications of their morphology upon suffering from an external agent.
Oxynitridation of cubic silicon carbide (100) surfaces
Authors: Amy F. , Douillard L. , Aristov V. Yu. , Soukiassian P.
Published: July 2002

The interaction of nitric oxide (NO) on Si-rich β-SiC(100) 3×2 surface reconstruction is investigated by photoemission spectroscopy using Al Kα (1486.6 eV) and Zr Mζ (151.4 eV) x-ray lines at Si 2p, C 1s, N 1s and O 1s core levels. NO exposures are performed at sample temperatures ranging from 25 to 1000 °C. The initial sticking coefficient of the NO molecules is found to be already significant at room temperature, with a dissociative adsorption resulting in Si oxynitride products as SiOxNy. The amount of oxynitride is significantly increased at surface temperatures of 500 °C and above. In addition, temperature is found to favor the formation nitrogen-rich SiOxNy oxynitride products. Thermal oxynitridation on the 3×2 reconstruction results in a SiOxNy/β-SiC(100) interface.
Thermal reaction of Pt film with 〈110〉 GaN epilayer
Authors: Gasser S. M. , Kolawa E. , Nicolet M.-A.
Published: July 2002

Backscattering spectrometry, x-ray diffractometry, and scanning electron microscopy have been used to study the reaction of a thin Pt film with an epilayer of 〈110〉 GaN on 〈110〉 sapphire upon annealing at 450, 550, 650, 750, and 800 °C for 30 min. A Ga concentration of 2 at. % is detected by MeV 4He++ backscattering spectrometry in the Pt layer at 550 °C. By x-ray diffraction, structural changes are observed already at 450 °C. At 650 °C, textured Ga2Pt appears as reaction product. The surface morphology exhibits instabilities by the formation of blisters at 650 °C and voids at 800 °C.
Investigation of 4% carbon in hydrogen electron cyclotron resonance microwave plasmas using ethane as the source gas
Authors: Webb S. F. , Gaddy G. A. , Blumenthal Rik
Published: July 2002

Supersonic pulse, plasma sampling mass spectrometry has been used to probe electron cyclotron resonance microwave plasmas consisting of 2% ethane in hydrogen and 2% ethane in deuterium. The overall hydrocarbon chemistry and interconversion of species within these plasmas were determined by comparing the composition of these two chemically equivalent plasmas. The ethane in hydrogen plasma is shown to consist of 58% unreacted ethane (C2H6), 16% ethylene (C2H4), 12% acetylene (C2H2), 9% methane (CH4), with the remaining 4% of the counts attributed to the ethylene radical species (C2H3) and the ethane radical species (C2H5). The mass spectrum of the analogous deuterium plasma reveals the ethane to remain entirely undeuterated, while the ethylene and acetylene exhibit significant deuteration. The observation of significantly deuterated ethylenes indicates a new reaction channel is available in these ethane-based plasmas, that is not available to hydrocarbon plasmas based on acetylene or ethylene. Specifically, the reaction of the ethane radical (C2H5) with a hydrogen atom results in the cleavage of the carbon–carbon bond forming two methyl radicals (CH3). Once formed, the methyl radicals may undergo repeated cycles of hydrogen (deuterium) atom additions and abstractions (analogous to those previously observed for acetylene) before recombining to yield the deuterated ethane radicals (C2DxH5−x) which then by abstraction of a hydrogen (or deuterium) forms the observed deuterated ethylenes. Overall, the chemistry of these hydrocarbon plasmas is shown to be completely consistent with the neutral molecule reactions previously observed in combustion chemistry literature.
Entrapment pump: Noble gas pump for use in combination with a getter pump
Authors: Watanabe Fumio , Kasai Akinari
Published: July 2002

A new type of minicapture pump which acts on noble gas species and operates in combination with a getter pump has been developed. We call it the “entrapment pump.” The pump is a single Penning cell (φ7×h5 mm anode) whose cathode can be heated during pumping to more than 1000 °C. After the getter pump is working, the pump cathode is activated by heating. Then, in a second step, the pump is operated by applying the high voltage and residual noble gas (argon) pumped by burial, not sputtering. Weakly buried noble gas within the pump cell is re-emitted by intentional heating. This is performed during every pumpdown following any exposure to atmospheric air and the surface of the cathode is thereby cleaned and renewed. As a result, noble gas atoms are buried in a pure metal surface when high voltage is applied and no burst of contamination species is generated from the cathode surface when the pump is initially started. The re-emission of previously pumped noble gas, acting as a gas source, is also minimized for low pressures. The pumping speed of the entrapment pump remains constant in the 10−8 Pa range. Therefore, the entrapment pump should be useful in attaining ultrahigh vacuum and extreme high vacuum in combination with getter pumps such as evaporable barium getters or nonevaporable getters.
Study on polymeric neutral species in high-density fluorocarbon plasmas
Authors: Teii Kungen , Hori Masaru , Ito Masafumi , Goto Toshio , Ishii Nobuo
Published: July 2002

Production and extinction processes of polymeric neutral species (CmFn;m⩾2) in electron cyclotron resonance C4F8 and CF4 plasmas have been studied by using a quadrupole mass spectrometer (QMS) employing low-energy electron attachment technique. This technique allows the detection of electronegative CmFn species as negative ions by scanning the attaching electron energy in the QMS typically in the range of 0–10 eV. In addition to the most abundant F− and CF3− signals resulting from dissociative attachment to various fluorocarbon species, pronounced attachment resonances of negative ions corresponding to the series of CmF2m±1− such as C3F7−, C4F9−, and C5F9− were primarily observed especially at low microwave powers and high pressures. The C4F8 plasma contained a large amount of polymeric species and a high fraction of reactive F-stripped species as compared to the CF4 plasma, providing evidence of a high potential of gas phase and surface polymerization in a low F/C ratio plasma. The amount and composition of polymeric species were examined by varying gas residence time and diluted hydrogen or argon concentration. At 20 mTorr, the overall amount of polymeric species was suppressed by enhanced gas flow with decreasing residence time, while a fraction of F-stripped species was increased. The amount of polymeric species was also suppressed with increasing diluted hydrogen, and the different behavior in the two plasmas was interpreted as the result of interactions between H atoms and polymeric species. The results provide insights into the kinetics and chemical activity of polymeric species in a high-density plasma as a practical etching source.
Ultrafast silicon based photodetectors
Authors: Buchal Ch. , Löken M. , Lipinsky Th. , Kappius L. , Mantl S.
Published: July 2002

We have fabricated different metal-silicon-metal photodetectors and characterized these devices for visible and near-infrared (IR) response. For wavelengths shorter than 1.1 μm, electron-hole pairs are generated in the Si. They are accelerated to saturation velocity and move towards the metal electrodes. For longer wavelengths, Si itself becomes transparent, but carriers are emitted from the internal semiconductor–metal interfaces. This so-called “internal photoeffect” is governed by different carrier dynamics, because “hot” electrons or holes are injected into the Si. Their significant excess energy leads to extremely fast electrical pulses. The resulting temporal response was measured with a new setup, using a Ti:sapphire laser and an optical parametric oscillator, which generates ultrafast optical pulses (170 fs) at IR wavelengths. Schottky-barrier emission from CoSi2, Cr, Ti, and Pt was investigated. A photodetector from Ti–Si–CoSi2 was excited with optical pulses of 1250 nm and showed an electrical pulse response of 3.2 ps full width at half maximum at 4 V bias. This is a record value. We can demonstrate, that under certain conditions an even faster response becomes possible.
Consistent, combined quantitative Auger electron spectroscopy and x-ray photoelectron spectroscopy digital databases: Convergence of theory and experiment
Authors: Seah M. P. , Gilmore I. S. , Spencer S. J.
Published: July 2002

Auger Electron Spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) have many aspects in common. Therefore, tests of aspects for one spectroscopy, applicable to the other, should be validated for both. Digital databases of elemental spectra for both AES and XPS have thus been measured using an electron spectrometer that has been fully calibrated for its intensity and energy axes. These databases of true spectra give absolute Auger electron yields and relative photoelectron yields. The AES data are measured for both 5 and 10 keV electron beam energies, whereas the XPS data are measured for both Al and Mg unmonochromated x rays at the magic angle. In addition to these we have measured reflected electron energy loss spectroscopy (REELS) data to provide a third database. The combination of these databases allows a refinement of the theories to obtain an overall convergence between theory and experiment. Improvements to the theory have been obtained by identifying three classes of parameter, those (i) for both AES and XPS, such as electron transport, the methodology of evaluation of peak areas, and the spectrometer response function, (ii) for AES only, such as the electron ionization cross section, backscattering, and specific electron backgrounds, and (iii) for XPS only, such as the photon-ionization cross section. Additionally, the use of REELS data for background subtraction seems significantly better than the use of any one single Tougaard universal cross section in the determination of the AES and XPS intensities in the databases. The formalism for quantitative analysis in AES and XPS, using relative sensitivity factors, has been revised to develop an accurate matrix-less formalism that is very simple for use by the analyst. This formalism, involving “average matrix sensitivity factors” rather than “pure element sensitivity factors,” has the same accuracy as the matrix formalism but its simplicity permits ready extension to systems beyond binary.
Adhesion effect of polyimide passivation layer on lead-on-chip die attachment
Authors: Jiang T. Tom , Bradbury Cynthia A. , Canavan Michael
Published: July 2002

Adequate die-to-lead frame adhesion is necessary for lead-on-chip (LOC) package integrity during and after the manufacturing process. Inadequate adhesion may result in a variety of defects such as die adhesion failure, marginal wire bond, broken wire, and bent leads, which ultimately lead to electrical failure [Mallik, US Patent No. 4,835,120 (May 1989); M. Amagai and E. Kawasaki, Mater. Res. Symp. Proc. 338, 185 (1994)]. Adhesion between the LOC tape and the polyimide passivation is affected by the surface properties of both materials. Understanding the relationships between these properties helps engineers eliminate inadequate adhesion at die attach and continuously improve the manufacturing process. To this end, die that exhibit inadequate adhesion at die attach are analyzed and compared with die that exhibit adequate adhesion characteristics. To focus on the surface chemistry and physical properties of the passivation layer, x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy (AFM), and surface energy are used. Molecular concentrations and orientations are investigated and related to inadequate adhesion at die attach.
Selective area growth of GaN on Si(111) by chemical beam epitaxy
Authors: Kim Esther , Tempez A. , Medelci N. , Berishev I. , Bensaoula A.
Published: July 2002

We demonstrate the selective area growth of GaN on SiO2-masked AlN/Si(111) and GaN/AlN/Si(111) wafers by chemical beam epitaxy (CBE) using triethyl gallium and ammonia. We investigated the selective nucleation process on Si wafers with oxide and nitride masks. The selectivity of the nucleation process was monitored in real time using time-of-flight mass spectroscopy of recoiled ions (TOF-MSRI). Our results show that TOF-MSRI peaks from mask-corresponding elements (Si and O or N) remain unchanged during GaN regrowth on continuous SiO2 layers or nitridated Si(111) within the condition range we explored. The selective growth was confirmed by ex situ scanning electron microscopy analysis. We also found that, depending on the growth conditions, CBE can be used for selective growth of both microcolumnar and planar GaN films. Room temperature photoluminescence studies revealed that both types of films are optically active, which could potentially lead to novel device concepts and applications.
Scanning tunneling microscopy study of surface morphology of Si(111) after synchrotron radiation stimulated desorption of SiO2
Authors: Gao Y. , Mekaru H. , Miyamae T. , Urisu T.
Published: July 2002

The surface morphology of Si(111) was investigated using scanning tunneling microscopy after desorption of surface SiO2 by synchrotron radiation illumination. The surface shows large regions of an atomically flat Si(111)-7×7 structure, and is characterized by the formation of single bilayer steps nicely registered to the crystal structure. This is in sharp contrast to Si(111) surfaces after thermal desorption of SiO2 at temperatures of 880 °C and above, where the surface steps are much more irregular. X-ray photoemission spectroscopy is also used to investigate the process of synchrotron radiation stimulated desorption.
Reactive ion etch of 150 nm Al lines for interconnections in dynamic random access memory
Authors: Stojakovic G. , Ning X. J.
Published: July 2002

Three different aluminum reactive ion etch (RIE) processes have been developed for manufacturing 175 and 150 nm line/space wiring patterns in multilevel interconnection. The three approaches vary in complexity: (1) Conventional organic antireflective coating (ARC) with a photoresist etch mask, (2) inorganic silicon oxynitride dielectric ARC with a photoresist etch mask, and (3) a physical vapor deposition tungsten cap layer used as a hardmask. The reliability performance for the 150 nm Al RIE lines scales with previous technologies at larger groundrules. The process windows for each key parameters are evaluated. It is also shown that the metal etch processes can be extended to even smaller ground rules with a line or space width to height aspect ratio as high as 5 without requiring a new tool set.
Characterization of process-induced charging damage in scaled-down devices and reliability improvement using time-modulated plasma
Authors: Noguchi Ko , Samukawa Seiji , Ohtake Hiroto , Mukai Tomonori
Published: July 2002

The charging damage from metal etching and dielectric etching was studied using metal–oxide–semiconductor devices with an oxide thickness of 1.9–6.0 nm, and the impact of the charging on reliability of scaled-down devices, as well as damage monitoring methods appropriate for each plasma process and oxide thickness, were investigated. For metal etching, in which the electron shading effect is a major cause of charging, hot carrier degradation dominated oxide degradation for oxides of 3.5–6.0 nm. For thinner oxides (<3.0 nm), however, a gate leakage failure dominated, but the failure rate decreased with gate oxide thinning below 3.0 nm and became negligibly small below 2.2 nm. For dielectric etching, the gate leakage current was an effective damage monitor. To detect the latent damage accurately, use of a high oxide electric field of 5–9 MV/cm was effective. Like the metal etching damage, the failure rate was lower for a thinner oxide of <3.0 nm. The hot carrier degradation was less sensitive to the dielectric etching damage. To realize a plasma process with low damage and thus to improve the device reliability, time-modulated (TM) plasmas were applied to the electron cyclotron resonance (ECR) metal etcher, the ultrahigh frequency (UHF) dielectric etcher, and the inductively coupled plasma (ICP) polysilicon etcher. These etchers all showed reduced charging damage compared to the conventional continuous-wave plasma. The estimated amount of charges that passed through the gate oxide was reduced to about 1/4 in the ECR metal etcher. The oxide yield improved by about two times in the UHF dielectric etcher. The density of oxide traps decreased in the ICP polysilicon etcher. Thus, an application of the TM plasma for etching is practical and effective for fabricating large scale integrated circuits with high yield and reliability.
Cesium-induced structural transformation from the Si(113)3×2 to the 3×1 surface
Authors: Hwang C. C. , An K. S. , Kim S. H. , Kim Y. K. , Park C. Y. , Kwon S. N. , Song H. S. , Jung K. H. , Kinoshita T. , Kakizaki A. , Kang T.-H. , Kim B.
Published: July 2002

Cesium-induced structural transformation from the Si(113)3×2 to the 3×1 surface has been investigated by using low energy electron diffraction and synchrotron radiation photoemission spectroscopy. We measured the change of work-function, core level (Si 2p,Cs 4d), and valence band spectra with increasing cesium deposition time. As previously reported, cesium induced the structural transformation from the Si(113)3×2 to the 3×1 surface at the initial stage of adsorption. Two shoulders (S1,S2) in Si 2p core level and one (SS1) of dangling bond surface states (SS1, SS2) in valence band spectrum from the 3×2 surface disappeared with the structural transformation to the 3×1. These results show that surface atoms in sp2- and s2p3-like configurations on the 3×2 surface are changed to sp3-like ones during the structural transformation. Therefore, the cesium-induced structural transformation seems to be related to the reduction of elastic energy by the donation of valence electrons from cesiums.