bluuebunny/crossref_metadata_2025 huggingface dataset:
A Totally Wet Etch Fabrication Technology for Amorphous Silicon Thin Film Transistors
Authors: Miri Amir Masoud , Chamberlain Savvas G.
Published: April 2011

We developed a totally wet etch processing technology for the fabrication of inverted staggered amorphous silicon thin-film transistors (TFTs) and circuits. In this technology we take advantage of highly etch selective KOH and HF base solutions for amorphous silicon and silicon nitride layers. Our technology is simple, reproducible, fully compatible with positive photo-resist lithography techniques, and suitable for mass production of amorphous silicon TFT based circuits. Using this process, we fabricated thin film transistors which have an effective mobility of 0.83 cm2 V−1 s−1, threeshold voltage of 2V and on/off current ratio of 107. In this paper we discuss the details of our fabrication process and report on the chemical conditions of the etching and deposition processes.
Excimer Laser Annealed Poly-Si TFT Technologies
Authors: Okumura Fujio , Sera Kenji , Tanabe Hiroshi , Yuda Katsuhisa , Okumura Hiroshi
Published: April 2011

This paper describes the excimer laser annealed (ELA) poly-Si TFT technologies in terms of excimer laser annealing of Si films, the leakage current, and the TFT stability. A laser energy density and a shot dependencies of TFT characteristics was analyzed by TEM, SEM, and Raman. The mobility increases with increasing not only the energy density but also the shot density. The mobility increase with the energy density is due to the grain size enlargement. On the other hand, the mobility increase up to 10 to 20 shots is due to a decrease of defects, including small grains, grain boundaries and defects inside grains. The contribution of grain-growth is small. The ELA TFT has a micro-offset structure to reduce the leakage current. Moreover, we have proposed a dynamic leakage current reduction structure. The combination of these technologies provides a sufficiently small leakage current for AMLCDs. The stability of the gate insulator was analyzed. The TFT shows negative threshold voltage shift under gate bias stress. This is due to water penetration and the subsequent field activated chemical reaction in the gate insulator. The dissociation of Si-OH bonds with hydrogen-bonded water was a fundamental contributor. The shift was suppressed sufficiently by hydrogen passivation. Obtained ELA TFTs;s have mobilities of over 100 cm2/Vsec, threshold voltages of less than 3 V, effective leakage currents of less than 10−13 A, and are stable more than 10 years.
Defect-Engineered Graded GexSi1-x Buffers on Si (001) with Extreme Low Threading Dislocation Density
Authors: Kissinger G. , Morgenstern T. , Morgenstern G. , Erzgräber H. B. , Richter H.
Published: April 2011

Stepwise equilibrated graded GexSii-x (x≤0.2) buffers with threading dislocation densities between 102 and 103 cm−2 on the whole area of 4 inch silicon wafers were grown and studied by transmission electron microscopy, defect etching, atomic force microscopy and photoluminescence spectroscopy.
A Study of Gettering Efficiency and Stability in Czochralski Silicon
Authors: McHugo Scott A. , Weber E. R. , Mizuno M. , Kirscht F. G.
Published: April 2011

Gettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.
Hydrogen Passivation of Shallow Dopants in InP Studied by Photoluminescence Spectroscopy
Authors: Balasubramanian Sathya , Kumar Vikram
Published: April 2011

The effect of hydrogenation on the photoluminescence (PL) of InP : Mg, InP : Zn and undoped n-InP is presented. An increase in the near band edge pl intensity due to passivation of non-radiative centers was observed in all the samples. A donor - acceptor pair transition was observed before hydrogenation in the InP : Mg sample and after hydrogenation in the InP : Zn sample due to the acceptor deactivation. In n-InP the enhancement of donor bound exciton after hydrogenation points to the absence of donor passivation.
Atomic Hydrogen in GaN
Authors: Neugebauer Jürg , Van de Walle Chris G.
Published: April 2011

Based on extensive first-principles total-energy calculations we study the electronic structure, atomic geometry and energetics of atomic hydrogen in cubic GaN. All charge states of hydrogen (H+, H0, H-) are examined. For H- the gallium tetrahedral interstitial site is energetically most stable. All other sites are much higher in energy, indicating a high diffusion barrier for H- in GaN. H+ favors positions on a sphere with a radius of ≈ 1 Å and a nitrogen atom in the center. Among these positions the nitrogen antibonding site is energetically most stable. An unexpectedly large negative-U effect (U = —2.5eV) indicates that H0 is unstable.
Inversion of Conductivity in p-Si after Ion Treatment
Authors: Buzynin Alexander N. , Luk–yanov Albert E. , Osiko Vyacheslav V. , Voronkov Vladimir V.
Published: April 2011

The results of electric parameters studies of silicon samples with unusual p-n junctions are presented. The junctions appeared after the treatment of homogeneous p-Si wafers by 1–5 keV energy argon ion irradiation at the temperature below 100°C and without doping by any n-type impurities. The model of this phenomena is discussed.
Probing Metal Defects in CCD Image Sensors
Authors: McColgin William C. , Lavine J. P. , Stancampiano C. V.
Published: April 2011

We have investigated the role of heavy metals in causing visible pixel defects in Charge Coupled Device (CCD) image sensors. Using a technique we call dark current spectroscopy, we can probe for deep-level traps in the active areas of completed image sensors with a sensitivity of 1 × 109 traps/cm3 or better. Analysis of histograms of dark current images from these sensors shows that the presence of traps causes quantization in the dark current. Different metal traps have characteristic dark current generation rates that can identify the contaminant trap. By examining the temperature dependence of the dark current generation, we have calculated the energy levels and generation cross sections for gold, iron, nickel, and cobalt. Our results show the relationship of these traps to the “white spot” defects reported for image sensors.
Electronic Properties of Ideal and Interface-Modified Metal-Semiconductor Contacts
Authors: Mönch Winfried
Published: April 2011

Barrier heights in metal-semiconductor contacts may be modified by interlayers. The effects of atomic interlayers are due to interface dipoles. With the restriction to nearest-neighbor interactions and monovalent interlayer atoms, they may be described as interface molecules which consist of an interlayer and a substrate atom. If the interlayers are thicker than a few atomic layers their two interfaces with the metal and with the semiconductor will be non-interacting. Both types of interfaces are described by the model that interface-induced gap states determine the alignment of the bands and the electronegativity difference describes the charge transfer across the interface. The present paper discusses and analyzes experimental data for H-modified diamond and silicon, Al/Si/GalnP, and metal/ Si3N4/Si Schottky contacts.
High Temperature I-V and C-V Characteristics of a Al/n-GaAs/In Schottky Barrier Type Device
Authors: Singh A. , Marcano N.
Published: April 2011

Al/n-GaAs Schottky barrier type diode was fabricated by thermal deposition of Al on chemically etched polished surface of (100) n-GaAs at a pressure of 4×10−6 Torr. Back ohmic contact to n-GaAs was prepared by thermal deposition of In, followed by a 90 min. anneal in Ar atmosphere at 390° C. The C−2 vs V characteristics were quite linear for reverse bias voltages in the range 0-4 V. Over the temperature range 300–360 K, the values of the barrier height and the net carrier density (Nd-Na), obtained from the C−2-V data, were in the range 1.33–1.26 V and 4.3×l0−16-5.0×l0−16 cm−3, respectively. The forward I-V data over the temperature range 300–400 K, indicated that the electrical current across the Al/n-GaAs Schottky junction was transported by the mechanisms of generation-combination (GR) in the space charge, thermionic emission (TE) and ohmic leak current. A value of (1.20±0.04) V for the zero bias barrier height was deduced from the temperature dependence of the TE reverse saturation current. The barrier height deduced from the I-V data was practically independent of temperature. The 20% change in Nd-Na with temperature, obtained from the C-V data, and important contributions of the GR and leak currents to the total forward current, suggested the presence of defect levels in the surface space charge layer in n-GaAs, which may be responsible for the discrepancy in the values of the barrier height obtained from the I-V and C-V data.
Reversible and Irreversible Light-Induced Change of Photoluminescence in Porous Silicon
Authors: Choi Suk-Ho , Mun Byoung-Hun
Published: April 2011

We have investigated the light-induced change of photoluminescence(PL) and its recovery in porous silicon. The exposure of the porous silicon to continuous laser light in vacuum results in the quenching of the PL intensity, which is almost fully recovered by simply keeping the samples in vacuum or in air at room temperature for a few days. When the light exposure is done in air, the PL spectra of the samples with initial PL peak at 800 nm are blue-shifted to the peak position at 740 nm and the samples with the initial PL spectrum peaked at 740 nm shows only a rise of PL intensity without any change of its peak position. Fourier transform infrared(FTIR) studies suggest that the light-induced change of PL in air is a irreversible process and occurs as a result of optically induced replacement of some of the Si-H bonds with O-Si-H bonds or adsorption of oxygen with hydrogen loss.
Bls Studies of Exchange Coupling in The Iron Whisker/Cr/Fe System
Authors: Cochran J.F. , Totland K. , Heinrich B. , Venus D. , Govorkov S.
Published: April 2011

Brillouin light scattering (BLS) and magneto-optic Kerr effect have been carried out on a series of specimens consisting of a Fe(001) whisker substrate upon which thin Cr(001) and Fe(001) layers have been deposited by means of molecular beam epitaxy in ultrahigh vacuum. The Fe film was 20 monolayers (ML) thick, and the Cr(001) films were grown having various thicknesses. It is demonstrated that BLS thin film frequencies measured in the saturated magnetic state with the thin film magnetization parallel with the applied magnetic field can be used to obtain the exchange coupling strength between the thin film and whisker magnetizations both for antiferromagnetic coupling and for ferromagnetic coupling, provided that the ferromagnetic coupling is not too strong. It is also shown that the coupling strength is extremely sensitive to the quality of the chromium growth: a small deterioration in the growth conditions has been found to reduce the exchange coupling by nearly a factor of two.
First Principles Calculation of Electrical Conductivity and Giant Magnetoresistance of ColCu Multilayers
Authors: Butler W. H. , Zhang X.-G. , Nicholson D. M. C. , Maclaren J. M.
Published: April 2011

We show that the Kubo formula can be used to calculate the non-local electrical conductivity of layered systems from first principles. We use the Layer Korringa Kohn Rostoker method to calculate the electronic structure and the Green function of Co/Cu/Co trilayers within the local density approximation to density functional theory. This Green function is used to calculate the conductivity through the Kubo formula for both majority and minority spins and for alignment and anti-alignment of the Co moments on either side of the Cu spacer layer. This allows us to determine the giant magnetoresistance from first principles. We investigate three possibilities for the scattering in Co/Cu/Co: (1) equal electron lifetimes for Cu, majority spin Co, and minority spin Co, (2) equal electron lifetimes for majority and minority Co, weaker scattering in Cu and spin dependent interfacial scattering, (3) electron lifetimes for majority and minority spin cobalt proportional to their Fermi energy densities of states and spin dependent interfacial scattering.
Calculation of Electrical Conductivity and Giant Magnetoresistance within the Free Electron Model
Authors: Zhang X.-G. , Butler W. H.
Published: April 2011

We use the model of free electrons with random point scatterers (FERPS) to calculate the electrical conductivity and giant magnetoresistance (GMR) for FeCr multilayer systems and compare our results with the experimental values. Our analysis suggests that the primary cause of the GMR in FeCr systems is regions of interdiffusion near the interfaces. We find that in the samples analyzed, these regions of interdiffusion occupy about 8.5Å of the magnetic layer near each interface.
Colossal Magnetoresistance in Thick La0.7Ca0.3MnO3 Films
Authors: Treece Randolph E. , Dorsey P. , Rubinstein M. , Byers J. M. , Horwitz J. S. , Donovan E. , Chrisey D. B.
Published: April 2011

Thick films (0.6 and 2.0 μm) of the colossal magnetoresistance (CMR) material, La0.7Ca0.3MnO3 (LCMO), have been grown by pulsed laser deposition (PLD). The films were grown from single-phase LCMO targets in 100 mTorr 02 pressures and the material deposited on (100) LaAlO3 substrates at deposition temperatures of 800°C. The deposited films were characterized by X-ray diffraction (XRD), magnetic field-dependent resistivity, and Rutherford backscattering spectroscopy (RBS). The LCMO films were shown by XRD to adopt an orthorhombic structure. Brief post-deposition annealing led to ~50,000% and ~12,000% MR effect in the 0.6 μm and 2.0 μm films, respectively.
A New Magnetooptical Effect Discovered on Magnetic Multilayers: The Magnetorefractive Effect
Authors: Jacquet J. C. , Valet T.
Published: April 2011

We show theoretically that the change in the magnetization structure of magnetic metallic multilayers under the application of a magnetic field shall be generally associated with a significant change of the refractive index. This constitutes a new magnetooptical effect: the magnetorefractive effect.

Optical transmission measurements under an applied magnetic field through [Ni80Fe20/Cu/Co/Cu] multilayers, in the light wavelength region between 2 μm and 20 μm, clearly demonstrate the existence of the predicted effect and are found in reasonnable agreement with the theoretical calculations.
Evolution of Nanoscale Ferromagnetic Particles in Co-Cr and Cr-Fe Alloys Observed by Atom Probe Field Ion Microscopy
Authors: Hono K. , Okano R. , Takanashi K. , Fujimori H. , Maeda Y. , Sakurai T.
Published: April 2011

With appropriate processing conditions, nanoscale ferromagnetic particles precipitate from nonmagnetic matrix phase in the Co-Cr and Cr-Fe systems. In these heterogeneous alloys, unique magnetic properties are observed. In order to correlate such magnetic properties with the microstructures, we have employed an atom probe field ion microscope (APFIM) and a three dimensional atom probe (3DAP). In the Co-22Cr thin film sputter-deposited at elevated temperatures (~500 K), both APFIM and 3DAP data convincingly showed that the film was composed of lamellae-like ferromagnetic and paramagnetic phases of approximately 8 nm in thickness. On the other hand, it was shown that the films sputter-deposited at ambient temperature was composed of s-Co single phase without significant compositional heterogeneity. Based on these observations, we conclude that phase separation progresses during the growth of the film on a heated substrate. In the Cr-Fe alloy, large negative MR was observed in the as-quenched alloy at liquid helium temperature. However, the MR behavior changes as the phase decomposition progresses by annealing. The change in the MR behavior observed in this alloy with various heat treatment conditions will be discussed based on the microstructural characterization results by APFIM and 3DAP.
Magnetic Properties of Embedded Rh Clusters in Ni Matrix
Authors: Li Zhi-Qiang , Hashi Yuichi , Yu Jing-Zhi , Ohno Kaoru , Kawazoe Yoshiyuki
Published: April 2011

The electronic structure and magnetic properties of rhodium clusters with sizes of 1 - 43 atoms embedded in the nickel host are studied by the first-principles spin-polarized calculations within the local density functional formalism. Single Rh atom in Ni matrix is found to have magnetic moment of 0.45μB. Rh13 and Rhl 9 clusters in Ni matrix have lower magnetic moments compared with the free ones. The most interesting finding is tha.t Rh43 cluster, which is bulk-like nonmagnetic in vacuum, becomes ferromagnetic when embedded in the nickel host.
Removal of Poly(Dimethylsiloxane) Contamination from Silicon Surfaces with UV/Ozone Treatment
Authors: Egitto F. D. , Matienzo L. J. , Spalik J. , Fuerniss S. J.
Published: April 2011

UV/ozone cleaning is known to be effective for removing thin organic contaminants, but removal of silicon containing contaminants is questionable. Organo-silicon contaminants, e.g., silicones, can result from a variety of integrated circuit chip and electronic packaging fabrication processes. In this investigation, films of poly(dimethylsiloxane) (PDMS) on silicon substrates, with and without a gold coating, have been used to simulate such contamination up to a thickness of 50 nm. Although treatment consistently reduced the advancing DI water contact angle, in some cases from a value greater than 100° to a value less than 5°, the hydrophilic nature of the treated surfaces was not due to complete contaminant removal, i.e., a significant amount of modified contaminant remained on the surface. High resolution x-ray photoelectron spectroscopy (XPS) in the Si 2p region suggest that O-Si-C bonds in the siloxane, observed prior to treatment, are converted to SiOx, where x is between 1.6 and 2. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. Deflection testing was used to evaluate the adhesion of an epoxybased adhesive to intentionally-contaminated silicon chips, before and after UV/ozone treatment. Although PDMS contamination induced loss of adhesion between the chip and the adhesive, complete conversion to silicon oxides by UV/ozone treatment of contaminants having a thickness of 5.0 nm has been demonstrated to restore adhesion to a value equivalent to that of uncontaminated silicon chip surfaces.
Nondestructive Characterization of Fiber-Matrix Adhesion in Composites by Vibration Damping
Authors: Gu Weiqun , Lu Guo-Quan , Wu H. Felix , Kampe Stephen L. , Lichtenstein P. Ross , Dwight David W.
Published: April 2011

Adhesion at fiber-matrix interface in fiber-reinforced composites plays an important role in controlling the mechanical properties and overall performance of composites. Among the many available tests applicable to the composite interfaces, vibration damping technique has the advantages of being nondestructive as well as highly sensitive. We set up an optical system to measure the damping tangent delta of a cantilever beam, and correlated the damping data in glass-fiber reinforced epoxy-resin composites with transverse tensile strength which is also a qualitative measurement of adhesion at fiber-matrix interface. Four different composite systems containing three different glass-fiber surface treatments were tested and compared. Our experimental results showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength.
Deposition of Ca+, Na+, Al+, K+ on Single-Crystal Si From DIH20: NH40H: H202 and DIH20: HCL: H202 as Analyzed by ToF-SIMS and SPV
Authors: Debusk Damon , Lowell John , Reich Fraser
Published: April 2011

The solutions DIH20: NH40H: H202 and DIH20: HCL: H202 have been used extensively in the semiconductor industry for the removal of transition and alkali metals from wafer surfaces. The former, when used in a ratio of approximately 5:1: 1 effects the wet oxidation removal of organic surface films and trace metals (Cu, Au, Ag, Ni, etc.) while the latter, in an approximate 6:1:1 ratio dissolves alkali ions and hydroxides of Al+3, Fe+3, and Mg+2 desorbing by complexing residual metals. Of concern is that these mixtures are known to plate out charged ionic species, particularly Fe, which remains on the Si surface after exposure to these solution. This effect adds an enhanced surface potential barrier which can be negative or positive depending on the concentrations of species deposited.

While the effects of Fe as deposited by the NH40H solution is well-known, we are concerned in this study with the deposition of Ca, K, and the lighter ions, Na and Al. Conventional analytical methods such as ICP-MS or AAS or TXRF have been used to detect these ions but are problematic since each has a limited range of detectable species or is destructive to the surface when used with VPD to increase resolution. In this study, we have verified the deposition of these species by a ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) analysis since it has the ability to detect the complete range of the desired ions. In addition, we have applied high-injection surface photovoltage (SPV) to obtain an average surface charge on each sample. To illustrate the use of these methods, we have applied them to the analysis of various closed acid processing systems. Our interest here is the amount of these selected ions being deposited from these solutions and the influence of using a standard canister or bulk acid supply system. Comparisons were also made to standard and megasonic RCA cleans and hot phosphoric nitride strips. We will discuss ToF-SIMS and how it was applied to analyze the addition of these charged trace ions. This work suggests that the problem of trace ion detection on Si must include the entire range of transition and alkali metals, and that ToF-SIMS is a promising analytical tool for this purpose.
Extremely Low Temperature Silicon Liquid Phase Epitaxy
Authors: Konuma M. , Silier I. , Gutjahr A. , Bauser E. , Banhart F. , Frey H. , Nagel N.
Published: April 2011

By liquid phase epitaxy (LPE) we have grown silicon layers on silicon and partially masked silicon at temperatures below 450 °C from Ga and Ga-In solutions. Oxidation of the cleaned silicon substrate surfaces before epitaxial growth has been prevented by a buffered hydrofluoric acid treatment. The epitaxial layers reached a thickness of 7 jim and were free of extended defects.

Low growth temperatures make it possible to grow silicon layers also on pre-treated glass substrates. The amorphous glass is first coated with a thin nano-crystalline silicon layer which is deposited by plasma processes from a mixture of SiH4/H2 gas. The grains in the silicon layers grown from Ga solution on glass have reached sizes up to 100 μm.
Computational Fluid Dynamic Modeling and Flow Visualization of an Enclosed Wet Processing System
Authors: Bay Steven T. , McConnell Christopher F. , Thomas Huw K. , Izenson Michael G. , Murthi Jayathi
Published: April 2011

With the goal of optimizing point-to-point etch uniformity in a continuous flow wet processing system, a comprehensive fluid dynamics study was undertaken. Aspects of this work included developing a computational, finite-element, fluid dynamic model; performing a series of empirical studies based on dye-injection with photo detection and video analysis; and observing platinumwire bubble generation with transparent wafers.

Various flow modification designs were tested including the base case of no inserted device, a stationary “spinner” insert, and a stationary “showerhead” insert. Unsteady, non-uniform, flow distribution and zones of substantial flow recirculation were observed in the case of using no flow modification device. These observations were confirmed with the computational fluid dynamic model.

Used in conjunction with the two different types of flow inserts, a new supplementary Teflon screen was designed and tested. The combined optimum configuration using this screen with an insert was then identified. Significantly enhanced point-to-point etch uniformity, with minimal recirculation and prompt fluid displacement, resulted from this design.
Monitoring Of HF/H2O Treated Silicon Surfaces Using Noncontact Surface Charge Measurements
Authors: Roman P. , Hwang D. , Torek K. , Ruzyllo J. , Kamieniecki E.
Published: April 2011

In this work, a new commercial system allowing non-contact measurement of the surface charge is used to monitor the condition of the silicon surface following HF/water etch. Results obtained demonstrate that by monitoring changes of surface charge using this system, a truly non-invasive, instant and easy to carry out characterization of Si surfaces after HF/water etch can be accomplished. The results show that HF/water exposure adds positive charge to the silicon surface. Change in the surface charge, considered to be indicative of the change in the electro-chemical condition of the surface, appears to precede initiation of the oxide etching process, and is proposed to be a factor in initiating etching reactions that involve mainly negatively charged species.
Electrochemical Aspects of Etching and Passivation of Silicon in Alkaline Solutions
Authors: Jeon Joong S. , Raghavan Srini
Published: April 2011

Electrochemical polarization experiments were performed on Si wafers in ammoniacal solutions maintained at a pH in the range of 9.5 to 11.5. Anodic polarization of silicon yielded curves which are typical for materials that undergo passivation. The values of open circuit potential and passivation potential for p-type Si wafers were more anodic than for the n-type Si wafers. Corrosion current density of p-type Si wafers of low resistivity was lower than that of wafers of high resistivity. Corrosion current densities correlated well with surface roughness induced in alkaline solutions. Addition of surfactant or H2O2 to alkaline solutions reduced critical current density for passivation and corrosion current density.
Advanced Properties of Silicon Oxynitride (SiOxNy) Thin Films Prepared by Pulsed Laser Deposition
Authors: Xiao R.-F. , Ng L.C. , Liao H.B.
Published: April 2011

A pulsed laser deposition technique has been used to grow silicon oxynitride (SiOxNy) thin films at low deposition temperatures (25°C - 300°C). the thin films were found to be quite smooth in surface morphology, extremely inert in chemical solution and highly transparent in the optical range of 0.3 μm to 5 μm. the refractive index was tunable between 1.4 - 2.1 by the addition of oxygen in substitution of nitrogen in the film, and the dielectric constant is much larger than the similar films grown by conventional chemical vapor deposition. the high quality of the SiOxNy films deposited at such low temperatures was resulted from the large kinetic energy carried by the impinging particles created by the ablation of a high-power pulsed excimer laser. the kinetic energy of the impinged particles on the substrate provides thermal energy for surface diffusion and relaxation.
Mechanism of ArF Laser induced Photolytic Deposition of W From WF6 on Etched Si and Unetched Si
Authors: Zhang Xiafang , Leary Herbert J. , Allen Susan D.
Published: April 2011

ArF excimer laser-induced photolytic chemical vapor deposition of W on etched Si substrates using tungsten hexafluoride has been studied. Our experimental results show that tungsten film thickness is proportional to the laser irradiation time and fluence, and that the deposition rate initially increases, then decreases with increasing WF6 pressure. the activation energy obtained from an arrhenius plot is much less than that for conventional CVD. a deposition mechanism has been proposed which yields results in good agreement with the experimental dat A. the absorption cross section of WF6 is determined to be 2.75xl0-18 cm2/molecule.
Solid Phase Epitaxy of Implanted Si-Ge-C Alloys
Authors: Lu Xiang , Cheung Nathan W.
Published: April 2011

Si1-x-yGexCy/Si heterostuctures were formed on Si (100) surface by Ge and C implantation with a high dose rate MEtal - Vapor Vacuum arc (MEVVA) ion source and subsequent Solid Phase Epitaxy (SPE). after thermal annealing in the temperature range from 600 °C to 1200 °C, the implanted layer was studied using Rutherford Back-scattering Spectrometry (RBS), cross-sectional High Resolution Transmission Electron Microscopy (HRTEM) and fourbounce X-ray Diffraction (XRD) measurement. Due to the small lattice constant and wide bandgap of SiC, the incorporation of C into Si-Ge can provide a complementary material to Si-Ge for bandgap engineering of Si-based heterojunction structure. Polycrystals are formed at temperature at and below 1000 °C thermal growth, while single crystal epitaxial layer is formed at 1100 °C and beyond. XRD measurements near Si (004) peak confirm the compensation of the Si1-x Gex lattice mismatch strain by substitutional C. C implantation is also found to suppress the End of Range (EOR) defect growth.
The Role of Ions for the Deposition of Hydrocarbon Films, investigated by In-Situ Ellipsometry
Authors: Von Keudell A.
Published: April 2011

The growth mechanisms for the deposition of hydrocarbon films (C:H-films) from a methane electron cyclotron resonance (ECR) plasma are investigated by means of in-situ ellipsometry. Ion bombardment during plasma-enhanced chemical vapor deposition of hydrocarbon films mainly governs the properties of the films and the total growth rate. the role of ions for the growth rate and the film properties is discussed in this paper. Films were deposited with varying RF-bias, resulting in a DC self-bias ranging from floating potential up to 100 V. the ion-induced modification of the film properties was investigated by a new technique using a double layer consisting of a polymer-like film with low optical absorption and a hard carbon film with high absorption on top. the interface between these layers was analysed after deposition by a layer-by-layer etching in an oxygen plasma at floating potential. From these data it is possible to determine with high accuracy the range of the ion-induced modification of the optical properties in the underlying polymer-like film. the thickness of this modified layer ranges from 6 Å at 30 V self-bias to 40 Å at 100 V self-bias, which is consistent with the range of hydrogen ions in polymerlike films as calculated by the computer code TRIM.SP.

Based on the presented results, the growth of C:H-films and the resulting film properties can be modelled by the growth at activated sites at the film surface. these activated sites are represented by dangling bonds, induced by the ion bombardment. they also show up in the ellipsometric results during the deposition of C:H-films by a change of the optical response of the film surface.
AFM Study of Surface Morphology of Aluminum Nitride Thin Films
Authors: Watanabe Yoshihisa , Nakamura Yoshikazu , Hirayama Shigekazu , Naota Yuusaku
Published: April 2011

Aluminum nitride (AlN) thin films have been synthesized by ion-beam assisted deposition method. Film deposition has been performed on the substrates of silicon single crystal, soda-lime glass and alumin A. the influence of the substrate roughness on the film roughness is studied. the substrate temperature has been kept at room temperature and 473K and the kinetic energy of the incident nitrogen ion beam and the deposition rate have been fixed to 0.5 keV and 0.07 nm/s, respectively. the microstructure of the synthesized films has been examined by X-ray diffraction (XRD) and the surface morphology has been observed by atomic force microscopy(AFM). IN the XRD patterns of films synthesized at both room temperature and 473K, the diffraction line indicating the alN (10*0) can be discerned and the broad peak composed of two lines indicating the a1N (00*2) and a1N (10*1) planes is also observed. aFM observations for 100 nm films reveal that (1) the surface of the films synthesized on the silicon single crystal and soda-lime glass substrates is uniform and smooth on the nanometer scale, (2) the average roughness of the films synthesized on the alumina substrate is similar to that of the substrate, suggesting the evaluation of the average roughness of the film itself is difficult in the case of the rough substrate, and (3) the average roughness increases with increasing the substrate temperature.
Mechanical Behaviour of Two Sorts of MCM Structures
Authors: Pozza G. , Parat G. , Ignat M. , Dupeux M. , Terriez J. M.
Published: April 2011

We analysed the mechanical response of samples, representing Flip-Chip bonded type structures. Two sort of distributions of the PbSn solder bumps, interconecting a chip to a substrate were investigated. The mechanical response was established from macroscopic shear and tensile tests. The microstructural evolution to complete mechanical failure, was observed during similar tests, but performed in a Scanning Electron Microscope. These in-situ tests revealed a preferential crack nucleation site in the samples, specific to one of the interfaces. A complementary numerical analysis was developed, for trying to explain the preferential crack opening site.
Failure Analysis of Aluminum Wire Bonds in High Power Igbt Modules
Authors: Dittmer Klaus J. , Poech Max H. , Wulff Frank W. , Krumm Martin
Published: April 2011

The reliability of high power Insulated Gate Bipolar Transistor (IGBT) modules is mainly limited by the aluminum wire bonds. Bond failure occurs due to fatigue fracture close to the welded interface inside the large bonding wire caused by thermal cycling at extreme operating conditions. This paper presents the results of the metallographic and electron microscopic examinations of the welded interface as well as fracture morphology investigations of failed parts after power cycling. Infrared thermal imaging and investigations of the stress/strain relationship analyze the differential expansion caused by temperature distribution and thermal expansion mismatch between large bonding wire and semiconductor.
Design of Epoxy Encapsulating Compounds for Highly Reliable Surface Mounting Semiconductor Devices
Authors: Ishii Toshiaki , Moteki R. , Nagai A. , Eguchi S. , Ogata M.
Published: April 2011

One of the most important subjects for semiconductor packages is preventing cracks which occur when the entire package is exposed to a soldering temperature of 215 to 260°C in the surface mounting technology. Cracking, as seen during temperature cycling tests is also a problem to be addressed. This paper reports the design of epoxy encapsulating compounds for highly reliable semiconductor devices which require the following properties: (1) toughness of matrix resin, (2) low moisture absorption, (3) high adhesion to insertions, and (4) reduction of thermal stress. The moisture absorption was lowered and the toughness was improved by using hydrophobic epoxy resins and high filler loading. The latter reduced the thermal stress, and it was effective for lowering the moisture absorption and increasing the fracture toughness of molding compounds. The reliability tests results were also considered in terms of physical properties of molding compounds.
Two-Dimensional Silicon/Ferroelectric Liquid Crystal Spatial Light Modulators
Authors: Drabik Timothy J.
Published: April 2011

Spatial light modulator (SLM) technology based on commodity silicon fabrication processes and employing a thin, ferroelectric liquid crystal light modulating layer at the chip's surface, has advanced to the point of producing high-performance, practically useful devices. Electrically addressed display devices with 256 × 256 resolution, 100: 1 contrast, and 10 kHz frame rate, as well as optically addressed, “smart” SLMs that perform spatio-temporal filtering on images, have resulted in the course of the author's involvement with Displaytech, Inc.

The silicon technology infrastructure is a juggernaut that produces regular and significant advances in capability. An optoelectronics technology based on foundry silicon can exploit these advances directly and realize rapid improvements. The gains in the density, speed, and optical performance of the Si/FLC devices presented here, illustrate this perspective.

The favorable speed-power performance of these devices is due to an excellent match in the “terminal characteristics” of FLC materials with those of fine-line MOSFETs. The impact of these characteristics on overall device performance is discussed in some depth.
The Growth of Optical Quality LiNbo3 Thin Films On Sapphire and LiTao3 Substrates Using Solid-Source Mocvd
Authors: Lee S. Y. , Route R. K. , Feigelson R. S.
Published: April 2011

High quality lithium niobate (LiNbO3) epitaxial thin films have been grown on c-plane sapphire and LiTaO3 substrates by solid-source MOCVD using the tetramethyl-heptanedionate sources, Li(thd) and Nb(thd)4. Phase content was controllable, and stoichiometric films were reproducibly deposited over a broad temperature range from a Li(thd)-rich source. Using sapphire substrates, with which the occurrence of multiple in-plane orientations is typically a problem, LiNbO3 films with only one in-plane orientation could be prepared within a narrow range of growth conditions. XRD rocking curve FWHM values as low as 0.04°, and optical waveguiding losses near 2dB/cm (1200Å thick film, TMo mode, 632.8nm) were obtained. However, film thicknesses on sapphire were limited to 2000Å because of cracking caused by the large thermal expansion mismatch, and in such thin films, optical confinement is poor.

In contrast, LiTaO3 has almost same lattice constants and thermal expansion coefficients as LiNbO3, making it a potentially superior substrate material. Lithium niobate films up to 6000Å were successfully deposited on LiTaO3 substrates without cracking. Film quality was greatly improved, with FWHM values as low as 0.01°, and rms surface roughness less than 10 Å. Preliminary optical waveguiding losses less than 6 dB/cm for the TEo mode have been achieved.
The Effect of Co-Dopants on the Photoluminescence of Er3+ in Silicon
Authors: Pradissitto J. J. , Federighi M. , Pitt C. W. , Gillin W. P. , James A. G. , Wilson R. J.
Published: April 2011

This paper presents the results of our investigation into the possibility of increasing both the radiative cross-section and the electrical activation efficiency in erbium (Er3+) doped silicon (Si). The energy levels of the isolated Er3+ have been theoretically predicted, employing the Thomas-Fermi method. The behaviour of these levels in Si was then investigated using a Kronig-Penney approach. Initial theoretical results imply that fluorine (F), in addition to Er3+ in Si, increases the radiative cross-section of Er3+ by at least an order of magnitude, and that co-doping appears to enhance the mixing of the 4f and 5d levels and causes the Er3+ energy levels to overlap with those of the host. Photoluminescence spectra of Er3+ in Si co-doped with F also indicate an interaction with the host lattice which appears to be dependent on its electrical characteristics.
Cationic Gelatin as a Gene Carrier
Authors: Brown K. E. , Bathon J. , Huang C. H. , Dalai R. , Leong K. W.
Published: April 2011

Cationic gelatin was evaluated as a non-viral vector for cell transfection. We hypothesized that cationic gelatin would be a nontoxic alternative to already existing viral and non-viral cationic vectors. Cationic gelatin was synthesized by modifying gelatin with hexanediamine. Complexation of cationic gelatin with psv-β-gal plasmid caused an electrophoretic mobility shift of the plasmid. Cationic gelatin/DNA complexes were optimized in terms of transfection efficiency in CHODUK XB1 and COS 7 cell lines. Maximal gene expression for both cell types occurred in serum free medium with chloroquine (100 μM) at cationic gelatin/DNA ratios of approximately 2 and 7. In comparison with DEAE dextran, polylysine and Lipofectamine, cationic gelatin was the most efficient in transfecting COS 7 cells, with up to 18% cells transfected. In a dye reduction cytotoxicity assay, cationic gelatin caused < 5% of cells to become nonviable at a concentration of 100 μg/ml, while the other transfection reagents tested at the same concentration caused 25–100% of cell death. These results suggest that cationic gelatin holds promise as an effective vehicle for gene delivery to mammalian cells.
Gallium Incorporation Kinetics During GSMBE of GaN
Authors: Jones Charles R. , Lei Ting , Kaspi Ron , Evans Keith R.
Published: April 2011

The kinetics of Ga incorporation during gas-source molecular beam epitaxy of GaN are investigated for varying substrate temperature and incident ammonia flux. Incident Ga atoms eventually either: 1) react with NH3 to form GaN, 2) accumulate on the film surface, or 3) desorb. Low substrate temperatures lead to significant Ga surface accumulation due to the temperature-dependent reactivity of NH3 towards Ga. High substrate temperatures give rise to significant Ga desorption. Increasing NH3 flux retards both Ga surface accumulation and Ga desorption. The GaN formation rate variation with substrate temperature peaks near 750°C and increases with NH3 flux. The observation of two distinct and very low activation energies for Ga desorption suggests a relatively complex surface chemistry and a strong likelihood that hydrogen is playing an important role.
Plasma-Assisted MBE of GaN and AlGaN on 6H SiC(0001)
Authors: Sinharoy S. , Agarwal A. K. , Augustine G. , Rowland L. B. , Messham R. L. , Driver M. C. , Hopkins R. H.
Published: April 2011

The growth of undoped and doped GaN and AlGaN films on off-axis 6H SiC substrates was investigated using plasma-assisted molecular beam epitaxy (MBE). Smooth and crack-free GaN and AlGaN films were obtained; the best results occurred at the highest growth temperature studied (800°C) and with a 40 to 50 nm A1N buffer layer grown at the same temperature. Carrier concentrations of up to n = 4 × 1020 cm−3 were accomplished with silicon, with a 40 to 50% activation rate as determined by secondary ion mass spectrometry (SIMS). Unintentionally doped AlxGa,.xN (x≈0.1) was n-type with a carrier concentration of 7 × 1018 cm−3. N-type AlGaN (x≈0.1)/p-type 6H SiC (0001) heterostructures showed excellent junction characteristics with leakage currents of less than 0.1 nA at 5 V reverse bias at room temperature and 0.5 nA at 200°C operating temperature.
Optoelectronic and Structural Properties of High-Quality GaN Grown by Hydride Vapor Phase Epitaxy
Authors: Molnar R.J. , Aggarwal R. , Liau Z.L. , Brown E.R. , Melngailis I. , Götz W. , Romano L.T. , Johnson N.M.
Published: April 2011

Gallium nitride (GaN) films have been grown by hydride vapor phase epitaxy (HVPE) in a vertical reactor design. We report on GaN growth directly on sapphire using a GaCl surface pretreatment. The electrical properties of these films compare favorably with the highest values reported in the literature for GaN. Specifically, a room temperature Hall mobility as high as 540 cm2 /V-s, with a corresponding carrier concentration of 2×1017 cm−3, have been attained. Additionally, the vesical reactor design has assisted in reducing nonuniformities in both film thickness as well as in transport properties due to depletion effects, as compared with horizontal designs. The dislocation density in these films has been determined by plan-view transmission electron microscopy to be ∼3×l08 cm−2 .

Photoluminescence spectra obtained at 2 K show intense, sharp, near-bandedge emission with minimal deep level emissions. Stimulated emission has been observed in these films, utilizing a nitrogen laser pump source (λ=337.1 nm) with a threshold pump power of ∼0.5 MW/cm2 . These results suggest that HVPE is viable for the growth of high-quality nitride films, particularly for the subsequent homoepitaxial overgrowth of device structures by other growth methods such as OMVPE and MBE.
An Atomic Force Microscopy Study of the Initial Nucleation of GaN on Sapphire
Authors: Richards-Babb M. , Buczkowski S. L. , Yu Zhonghai , Myers T. H.
Published: April 2011

Preliminary results of a study of GaN nucleation and growth by molecular beam epitaxy using a nitrogen rf plasma source are presented. Nucleation layers and 3000 Å thick layers were investigated by atomic force microscopy and x-ray diffraction. Growth under gallium-rich conditions both increased nucleation island size and promoted two-dimensional growth.
Low Temperature Growth of Oriented Gallium Nitride using Pulsed Laser Deposition
Authors: Leuchtner Robert , Brock W. , Li Y. , Hristakos L.
Published: April 2011

Oriented GaN has been successfully grown at low substrate temperatures (∼480°C) on a- and r-planes of sapphire, using the pulsed laser deposition process. We have examined the effects of several deposition parameters on film growth, including substrate temperature (∼50–500°C), ambient pressure (1×10−3 – 10 torr of NH3), and target material (Ga or GaN). The film deposition rate was typically ∼3–4 μm/hr. Film characterization was performed using x-ray diffraction (XRD), optical microscopy, x-ray photoelectron spectrometry (XPS), and atomic force microscopy (AFM). In the case of the Ga metal target, a plasma (∼500V) between the target and substrate was necessary to promote formation of the GaN phase. The ammonia ambient enhanced the nitrogen content in the films compared to vacuum deposition. In general, the GaN target yielded better quality films (smaller rocking curve widths and smoother film morphology) compared to the Ga metal target. These results suggest that pulsed laser deposition is a promising approach to fabricating high quality films of this potentially important semiconducting material.
Electronic Structures of Wide Band-Gap (AlN)m(GaN)n[001] Superlattices
Authors: Tian Z.-J. , Dharma-Wardana M.W.C. , Lewis L.J.
Published: April 2011

Wide bandgap III-V nitrides, such as GaN and AlN, have become topical in the near-term technology of blue lasers. We report detailed electronic band-structure calculations for (AlN)m(GaN)n [001] zinc-blende superlattices (SL), with m + n ≤ 12, using the all-electron full-potential linear-muffin-tin-orbital method. For n ≥ 3, the SL are found to have a direct band gap. For n ≤ 2 and m ≥ 3, all the band gaps are indirect. In ultrathin SL, m ≤ 3 and n ≤ 2, only (m, n)= (3,1) is found to have an indirect gap. The band offsets are estimated by calculating the core-level shifts of nitrogen atoms in the central planes of the GaN and A1N layers. The calculated densities of states, electron- and hole- effective masses (m), etc., as a function of m and n, are reported; a remarkable dependence of m on the number of layers is revealed.
ScAlMgO4: An Oxide Substrate for GaN Epitaxy
Authors: Hellman E. S. , Brandle C. D. , Schneemeyer L. F. , Wiesmann D. , Brener I. , Siegrist T. , Berkstresser G. W. , Buchanan D. N. E. , Hartford E. H.
Published: April 2011

We report the use of ScAlMgO4 as a substrate for the epitaxial growth of wurzitic GaN. The low misfit (+1.8%) allows coherent epitaxy of GaN, as observed by RHEED. The congruent melting of ScAlMgO4 makes Czochralski growth possible, suggesting that large, high quality substrates can be realized. Boules about 17mm in diameter are reported. We have used nitrogen-plasma molecular beam epitaxy to grow GaN epitaxial films onto ScAlMgO4 substrates. Band-gap photoluminescence has been observed from some of these films, depending primarily on the deposition conditions. A 3×3 superstructure has been observed by RHEED on the GaN surfaces. Structural analysis by x-ray diffraction indicates very good in-plane alignment of the GaN films. We also report thermal expansion measurements for ScAlMgO4.