bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled Nitrogen-Atom Incorporation At Si-SiO2 Interfaces in Mis Devices
Authors: Lee David R. , Parker Christopher G. , Hauser John R. , Lucovsky Gerald
Published: April 2011

We have developed a new pre-deposition, remote N2O plasma oxidation treatment for forming nitrided SiO2 films and report here the quality and reliability of devices fabricated with these films. The Si-dielectric heterostructure process has been separated into three independently-controlled steps: i) final Si surface cleaning, and Si – SiO2 interface formation by plasma-assisted oxidation/nitridation at 300 °C; ii) remote plasma-enhanced chemical vapor deposition of nitrided dielectrics, also at 300 °C; and iii) optional post-deposition rapid thermal annealing. This paper focuses on the first step in which the oxidation has been performed with O2, N2O or N2O / O2 mixtures to control the amount of N-atoms at the interface, Nint. We show that the incorporation of up to ∼ 1015 N-atoms/cm2 at the Si-SiO2 interface by this process has no effect on threshold voltage, Vt, or peak channel transconductance, gm,max, but does improve high-field gm and transistor drive current. Improved resistance to Vt and gm,max degradation during hot-carrier stressing of sub-micron devices is also discussed.
Advanced Technology Processing and State-of-the-art Solutions to Cleaning, Contamination Control, and Integration Problems
Authors: Abadeer W. W. , LeBlanc A. , Kluwe A. , Schulz P. , Vollertsen R. , Penka V. , Nadahara S. , Antreasyan A. , Cote D. , Cote W. , Levy M. , Akatsu H. , Ludeke R.
Published: April 2011

Ultraclean semiconductor processes were developed for ULSI technologies to significantly reduce metallics, foreign materials, and to preserve silicon surface morphology. State-of-the-art detection techniques (Elymat, TXRF, VPD, and SPV) were implemented in all critical process sectors. Acceptable levels of metallic contamination were derived from previous experience and from published work on this subject relating metallic contamination levels to gate oxide reliability and retention time.

A comprehensive diagnostic/characterization system was utilized in evaluating a wide variety of test structures emulating key device process interactions. Advanced techniques were employed for measurement of reliability and surface morphology. Also root causes for all integration problems are identified.
Wafer Cleaning Influence on the Roughness of the Si/SiO2 Interface
Authors: Munkholm A. , Brennan S. , Goodbread Jon P.
Published: April 2011

The roughness of the Si/SiO2 interface has a great impact on the electrical properties of the gate-oxide in integrated circuits and consequently it is a large concern for the semiconductor industry. As the thickness of the oxide is decreased, the role of the roughness becomes more critical for the device. The nature of a buried interface prohibits the use of commonly used surface techniques. By the use of crystal truncation rod (CTR) x-ray scattering, it is possible to get information on the termination of the bulk silicon in a nondestructive fashion. The authors have investigated the influence of different cleanings on interfacial roughness using synchrotron radiation-based CTR-scattering. In particular, we looked at silicon(001) wafers both before and after the growth of a 1000Å thermal oxide. The results show that the use of HF during cleaning results in a smoother interface between silicon and its native oxide. Due to smoothing of the interface during the oxidation process, the difference between the various cleaning methods becomes less significant for these thick oxides.
Mechanisms of Excimer Laser induced Positive Ion Emission From Ionic Crystals
Authors: Dickinson J. T. , Shin J-J. , Langford S. C.
Published: April 2011

The energy distributions of positive ions produced by exposing single-crystal MgO to pulsed 248 nm excimer laser light at fluences of 200-1200 mJ/cm2 were determined by combined quadrupole mass spectrometry and time-of-flight techniques. the dominant ionic species is Mg+, although small amounts of Mg2+, MgO+, and Mg2O+ are also observed. IN particular, the

Mg+ and Mg2+ energy distributions each show two broad peaks, with the energies of the Mg2+ peaks at significantly higher energies. Ion trajectory simulations (accounting for Coulomb forces only and assuming no surface relaxation) suggest that Mg2+ adsorbed at sites directly atop surface F-centers (oxygen vacancies with two trapped electrons) would be ejected upon photo-ionization of the F-center. the experimentally observed Mg2+ kinetic energies agree well with the energies predicted by the simulation.
Ion-Assisted Pulsed Laser Deposition of BN Films
Authors: Doll G. L. , Chance D. C. , Salamanca-Riba L.
Published: April 2011

Boron nitride films grown by ion-assisted pulsed laser deposition have been characterized by infrared absorption, auger electron pectroscopy, and transmission electron microscopy. Elemental bonding and the crystallinity of BN films grown in three nitrogen ion energy regimes:high (2500 eV), low (700 eV), and without ions (0 eV) are examined, and the results interpreted within the framework of a compressive stress mechanism for cBN film growth.
Carbon Nitride Films Using a Filtered Cathodic ARC
Authors: Camphausen Scott.M. , Tucker D.A. , Bruley J. , Cuomo J.J.
Published: April 2011

Carbon nitride films were deposited on sapphire, silicon, molybdenum and quartz substrates using a filtered cathodic arc with a radio frequency (rf) inductively coupled plasma, Previous researchers have used the cathodic arc but obtained low concentrations of nitrogen in their films. the addition of the rf coils was used to enhance dissociation of molecular nitrogen in the vicinity of the substrate. the resultant films were analyzed for chemical bonding and composition by several methods including Electron Energy Loss Spectroscopy (EELS), augei Electron Spectroscopy (AES), and infrared spectroscopy (IR). EELS and IR provided bonding information and showed that the films were largely composed of sp2 bonding and contained carbon-nitrogen double bonds, respectively. also, chemical composition of the films was determined using aES, IR and EELS.
High-Rate Deposition of Thin Films by High-Intensity Pulsed Ion Beam Evaporation
Authors: Zakoutayev A.N. , Remnev G.E. , Ivanov Yu.F. , Arteyev M.S. , Matvienko V.M. , Potyomkin A.V.
Published: April 2011

A high-intensity ion beam (500 keV, current density 60 - 200 a/cm2, power density (0.25 - 1) • 108 W/cm2, pulse duration 60 ns, pulse repetition rate 4-6 mur-1) was used to deposit thin metal and carbon films by evaporation of respective targets. the instantaneous deposition rate was 0.6 - 5 mm/s. the films were examined using transmission electron microscopy and transmission electron diffraction. the metal films had a poly-crystalline structure with the grains measuring from 20 to 100 nm, the lower the melting point the greater the grain size. the carbon films contained 25 - 125 nm diamonds. the ablation plasma was studied employing methods of pulsed spectroscopy.
Chemical Effects of substrate Temperature and Feed Gas Composition on Ion Beam Deposited AlN and AlN:H
Authors: Huang L. , Wang X. D. , Hipps K. W. , Mazur U. , Dickinson J. T. , Heffron R.
Published: April 2011

Direct ion beam sputter deposition of alN is studied using both pure nitrogen and a 75% N2/25% H2 mixture as the feed gas for the ion gun. the chemical characteristics of these films are probed using infrared spectroscopy and chemical etching. the presence of al-N2 species is associated with reactive and highly defective films. the presence of NHX species increases by several orders of magnitude the rate at which alN film are etched by base. However, stoichiometric and low defect alN films prepared by depositing alN:H onto substrates heated to 200 °C have reactivities similar to the best alN films produced in the absence of hydrogen.
Conductance Measurements of Thermally Annealed, Si-Implanted Quartz
Authors: R.Hodges Alex , Farlow Gary C.
Published: April 2011

Preliminary conductance measurements of Si implanted, α-Quartz which had been annealed in ar to 1000• C have been made using a bridge method. the quartz was implanted to a dose expected to yield Si precipitates inside the quartz upon annealing. the measured conductivity, based on a geometry deduced from TRIM calculations and several trans-conductance measurements, is ~ 2 х 10-4(Ω m)-1. This is consistent with large islands of Si in series with an insulating matrix.
Thin Film Polymer Stress Measurement Using Piezoresistive Anisotropically Etched Pressure Sensors
Authors: Monk David J. , Shah Mahesh
Published: April 2011

Stresses in thin polymer films have been studied for some time by using wafer bowing, bending beams, microstructure release, and laser holographic techniques. An alternative technique for measuring stresses in thin films is discussed in the following paper. Piezoresistive anisotropically etched single crystal silicon pressure sensors are sensitive not only to applied pressure, but also to applied package stress. Deposited passivation materials, like silicone gels and polyimides, have been observed to change the sensitivity of the pressure sensor. In the current work, a thin, conformal polymeric coating (parylene C) is being developed for these pressure sensors. This thin film has been observed to reduce the sensitivity of the device as a function of the film thickness and modulus and the silicon thickness and modulus. The parylene C thin films exhibit a consistent change in film stress during annealing indicating a modification to polymer crystallinity and a corresponding change in material properties. Qualitatively, the electrical output on the pressure sensor compares favorably with measurements taken using wafer bowing. Experimental DMA and TMA work has been performed to determine the modulus (7.84 × 105 psi) and CTE (39 ppm/°C at 25 °C) of the material. However, literature values of modulus (4.1 × 105 psi) have been used with finite element analysis to model the stress effect more accurately for the thin conformal coating on the pressure sensor device. These results indicate that the sensitivity of the pressure sensor will be reduced approximately quadratically as a function of the polymer coating thickness. An empirical function has been derived to estimate sensitivity loss as a function of substrate (i.e., initial diaphragm material) modulus and thickness and coating modulus and thickness.
Characterization of Films Formed during the Corrosion of Copper in Dilute Solutions of Cupric Chloride
Authors: Walsh L. H. , Feilchenfeld N. B.
Published: April 2011

Microstructural differences in copper deposited by four techniques commonly used in the microelectronics industry were previously reported. Grain size, preferred orientation, and near surface chemistry were considered. [1] Prediction of the reaction rates were made based on these differences and then correlated with actual measurements. [2] In aerobic conditions the grain size dictated the reaction rate, the smaller the size the faster the rate.[3] The composition of the surface film formed during etching was examined. The trends in chemical concentrations on the surface film vary for each sample, but the relative constituent amounts correlate to the grain size of the original copper samples. Thus, there is further evidence that during exposure to aqueous solutions of cupric chloride, copper corrosion, in terms of both etch rate and film composition, is dictated by grain size of the original copper and not other microstructural factors.
High Thermal Conductivity Graphite Copper Composites with Diamond Coatings for Thermal Management Packaging Applications
Authors: Stoessel Chris H. , Pan C. , Withers J. C. , Wallace D. , Loutfy R. O.
Published: April 2011

High thermal conductivity heat sinks for thermal management in electronic packaging is enabling to a variety of advanced electronic applications. Heat sinks in industrial semiconductor application have thermal conductivities generally less than 180 W/mK, and frequently have large expansion mismatch with chips such as silicon and gallium arsenide. A unique technology of producing graphite fiber reinforced copper (Cf/Cu) composite has been developed that produced thermal conductivities up to 454 W/mK utilizing a K=640 W/mK fiber reinforcement (with a potential for 800 W/mK when utilizing a K = 1100 W/mK P130 fiber) and thermal expansion that can be matched to chip materials. The process consists of utilizing a hollow cathode sputtering process to deposit a bonding layer followed by copper on spread graphite fibers, which are then consolidated into composites with architectures to achieve desired thermal conductivity and thermal expansion. The copper thickness determines graphite fiber loading up to 80 %. In heat sink applications, where the electrical conductivity of the graphite fiber reinforced copper composite is a problem, processing has been developed for applying electrically insulating diamond film, which has high thermal conductivity and acts as a heat spreader.
Wetting Behaviors of Sn-Based Solders on Cu and Pd Surfaces
Authors: Kim H. K. , Wang Y. , Maheshwari A. , Tu K. N.
Published: April 2011

We have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and pure Sn on Cu and Pd surfaces. In the case of Pd, the reactions were so fast that no quasi-equilibrium wetting angle could be measured. The compound formation has changed not only the interfaces but also the surfaces. Due to the formation of a reaction band outside the solder cap, the SnPb solder is no longer wetting the Cu surface but rather the Cu-Sn compound surface. In the wetting interface between eutectic SnPb and Cu, the morphology of the scallop-like Cu-Sn compound grains shows that we may not apply the classical model of layered compound growth to analyze the rate of soldering reactions.
The Use of Secondary Ion Mass Spectrometry to Investigate Wire Bonding Yield Problems on Gold Contacts
Authors: Mount G. R. , Walzak T. L. , Koo Y. C. , McClure D.
Published: April 2011

With ongoing demand for high density wiring and high I/O on VLSI chips, the requirement of high wire bond yield is a challenge to achieve low cost, high performance and reliable products. Secondary Ion Mass Spectrometry (SIMS) was used to investigate the metallurgical contaminants on the gold wire bond pads and their impact on wire bond yields. SIMS depth profile studies showed that copper and nickel in concentrations greater than 1 wt% caused poor wire bondability, while copper concentration at less than 0.1 wt% resulted in good bondability of Al ultrasonic wire bonded to the gold pads.
Fabrication of Er Doped Glass Films as Used in Planar Optical Waveguides
Authors: Gates J. V. , Bruce A. J. , Shmulovich J. , Wong Y. H. , Nykolak G. , Barros M. R. X. , Ghosh R.
Published: April 2011

Silica integrated optical circuits are expanding in functionality to include optically active waveguides. Traditionally, the planar optical waveguide structures include silica based glass films such as thermal oxides, phosphorous, and boron-phosphorous doped glasses. Various efforts have successfully doped conventional waveguides with Er, typically by solution doping. Material issues such as rare earth solubility and glass structure dictate that efficient optical amplifiers based on such waveguides have path lengths in excess of 10–15 cm. We have developed an alternative strategy using Er-doped soda-lime silicate glass films on silicon. The waveguide processing utilizes methods of deposition similar to those used in silicon IC technology, with modificatons in the compositions and thicknesses. In these glasses the effective solubility limits are relaxed and we have successfully fabricated short path length devices which demonstrate net gain of more than 4 dB/cm. Short path length devices offer a potential advantage in highly integrated multi-channel devices and offer an additional building block in system architectures.
Characterization of Magneto-Optical Rare Earth-Doped Ingaasp Thin Films on InP
Authors: Stadler B. J. , Vaccaro K. , Davis A. , Martin E. A. , Ramseyer G. O. , Lorenzo J. P.
Published: April 2011

We have investigated the properties of rare earth-doped InGaAsP thin films with special interest in magneto-optical device applications. Magneto-optical properties have been used in optical systems as isolators, waveguides, and switches. These materials and devices can be used to expand the functionality of InP opto-electronic integrated circuits (OEICs). Thin films of InP, InGaAs, and InGaAsP, grown by liquid phase epitaxy, were lattice matched to the (100) InP substrates. The films were n-type, with the carrier concentration decreasing by an order of magnitude in the doped films due to gettering by the rare earth elements. The doped films contained 2.6×1018 - 1.5×1020 cm−3 rare earth elements, which were observed to segregate toward the film/melt interface in the more highly doped films. A broad photoluminescence was observed at 1.52 μm in the Er-doped films. The Verdet constant was measured through the sample thickness, and the substrate signal dominated the measurements. However, the measured values were in agreement with published values for InP, which gives an indication of the films' host value. The Verdet constants increased from 4 to 7 deg/T/mm as the wavelength decreased toward the band edge. The band edges of our samples were 0.93, 1.62, and 1.30 μm, respectively. Rare earth dopants were observed to raise the refractive index of the InP films, and waveguiding at 1.3 μm was achieved in the rare earth-doped InP films and in the InGaAsP films.
In-Vivo Degradation of a Poly(Propylene-Fumarate) Biodegradable, Particulate Composite Bone Cement
Authors: Frazier Daveed D. , Lathi Vijay K. , Gerhart Tobin N. , Altobelli David E. , Hayes Wilson C.
Published: April 2011

We have developed a biodegradable particulate composite bone cement consisting of a poly(propylene glycol-fumarate)-(methylmethacrylate) matrix mixed with calcium carbonate and tricalcium phosphate particulates. Previous ex-vivo studies suggest that this system provides sufficient strength for a number of potential clinical applications including structural reinforcement of osseous defects, supplementation of internal fixation of age-related fractures, and delivery of antibiotics to treat osteomyelitis. Ex-vivo degradation assays have also shown that the cement approximates physiologic conditions of bone remodeling as it degrades. In order to evaluate the in-vivo responses to this material, we implanted cement specimens subcutaneously in rats for up to 84 days. Compressive strength of the subcutaneous implants increased linearly through day 21 to 4.91 MPa, then decreased linearly by day 84 to less than 1 MPa. We conclude that this PPFMMA system is biocompatible and biodegradable, and has the potential for use as an orthopedic bone cement. Future studies will be directed toward characterizing the intraosseous histological response and at coordinating the rate of cement degradation with bony ingrowth.
Wear Evaluation of Ultra High Molecular Weight Polyethylene Using Pin-On-Flat and Hip Simulation Techniques
Authors: Schroeder David W. , Higgins Joel C.
Published: April 2011

Reduction of wear and wear debris is one of the most important areas of research presently in the field of orthopedic devices. It is speculated that wear debris is one of the contributing factors in the cascade of events that lead to osteolysis. In this regard it is very important to be able to evaluate in vitro the wear of UHMWPE produced by various manufacturing methods. Presently the three most common methods of wear testing are: pin-on-flat, pin-on-disk, and hip simulator.

Wear evaluation was performed on gamma irradiated UHMWPE that was manufactured by three different processes: extrusion, direct compression molding, and isostatic compression molding. The wear evaluation consisted of pin-on-flat and hip simulator testing.

omparison of the results from these two different types of tests show that the two tests would rank the wear resistance of the UHMWPE in the same order. However, there is a variation in the difference of the wear rates between the two tests. The pin-on-flat results show that the direct and isostatic compression molded material had approximately 50% less wear than the extruded material whereas the hip simulator results show that the isostatic compression molded material had 16% less wear than the extruded material. The difference in the results of these two tests are the effects of a combination of factors including the mechanical and material properties of the UHN4WPE, modes of wear that are active, the state of stress (constant vs. cyclic) in the specimens, third body contamination of the lubricant, bacterial degradation of the bovine serum lubricant, etc. Both tests are very important and necessary in the evaluation of wear of orthopedic materials.
Bioactive Molecules Delivered by Ceramic Nanoparticles Coated with a Film of Polyhydroxyl Oligomers
Authors: Kossovsky Nir
Published: April 2011

The structural denaturation of polypeptides and other macromolecular pharmaceuticals upon surface adsorption from an aqueous environment is almost inevitable. Molecular denaturation, coupled with a net increase in entropy, accounts for the net negative ΔG and frequent irreversible nature of surface adsorption. The consequence of this interaction is that surface immobilized drugs lose their dynamic freedom and thus, all too often, their biological activity.

This phenomenon has complicated the development of drug delivery vehicles. In this communication, a drug delivery system based on a novel surface modification process to help reverse the constraining activity of surfaces is described. Beginning with preformed carbon ceramic nanoparticles and self-assembled calcium-phosphate dihydrate particles (colloidal precipitation) to which glassy carbohydrates are then allowed to adsorb as a nanometer thick surface coating, a molecular carrier is formed. The carbohydrate coating functions as a dehydroprotectant and stabilizes subsequently non-covalently bound immobilized members of biochemically reactive surface members such as pharmaceuticals.

Many of the physical properties of this enabling system have been characterized in vitro and in animal models. Antigen delivery, drug delivery, and enzyme stabilization experiments are described.
Growth Kinetics and Structural Quality in GaN Epitaxy by Low Pressure MOVPE
Authors: Briot O. , Alexis J.P. , Gil B. , Aulombard R.L.
Published: April 2011

GaN epilayers have been grown using low pressure MOVPE (76 Torr) onto (0001) sapphire substrates. Triethylgallium (TEGa) and Ammonia (NH3) were used as precursors. The growth rate has been determined versus growth parameters. The growth rate versus NH3 flow displays a rather unusual behavior, in particular at low growth temperature (buffer layer), where the growth rate decreases strongly when the NH3 flow increases. A growth mechanism involving a competitive adsorption step onto the surface is proposed, and results in a strong dependence of the growth rate on the V/III ratio.

The structural quality of the layers has been assessed by X-ray diffraction versus the growth parameters, and will be reported here. A substrate nitridation step, prior to buffer layer deposition has been introduced in our growth process. The effect of substrate nitridation on the structural and optical properties of the epilayers is studied and we propose an optimized pre-treatment for the MOVPE growth of GaN onto (0001) sapphire substrates.
A Study of the Effect of Growth Rate and Annealing on GaN Buffer Layers on Sapphire
Authors: Ramer J.C. , Zheng K. , Kranenberg C.F. , Banas M. , Hersee S.D
Published: April 2011

Using atomic force microscopy (AFM) and X-ray diffraction (XRD) we have determined that on [0001] oriented sapphire, the GaN buffer layer shows a degree of crystallinity that is dependent on growth rate. Annealing studies show evolution of the crystallinity and the emergence of a preferred orientation. Also, substrate orientation is found to influence the buffer layer crystallinity. Based on this work and previous results, we propose that the GaN buffer layer growth can be described by the Stranski-Krastanov growth process.
AlN Films Deposited by LP-MOCVD Atomic Layer Deposition at Lower Temperatures Using DMEAA and Ammonia
Authors: Kidder J.N. , Kuo J. S. , Pearsall T.P. , Rogers J.W.
Published: April 2011

We have investigated the deposition of AlN thin films on Si(100), Al2O3(0001), and Al2O3(0112) substrates at lower temperatures (523–723 K) using a novel aluminum source, dimethylethylamine:alane (DMEAA), with ammonia as a nitrogen source in a low-pressure MOCVD atomic layer growth process. At reactor pressures of 25 and 50 Torr a four-step sequence of reactant flow steps separated by flush steps was cycled. We observed a tendency toward a self-limiting growth rate as the DMEAA step flow time was increased. The deposition uniformity was observed to be dependent on temperature and non-uniform deposition occurred at higher temperatures. The microstructure and crystalline orientation were examined using x-ray diffraction and crystalline A1N films were deposited at temperatures as low as 573 K. Crystallite size decreased with substrate temperature and at 523 K. amorphous films were deposited. At T > 650 K preferentially oriented crystalline films were deposited with orientations of Si(100)//AIN(0001), Al2O3(0001)//AIN(0001), Al2O3(0112)//AIN(1120).
Facets Formation Mechanism of GaN Hexagonal Pyramids on Dot-Patterns via Selective MOVPE
Authors: Hiramatsu Kazumasa , Kitamura Shota , Sawaki Nobuhiko
Published: April 2011

Three-dimensional GaN pyramids have been successfully obtained on dot-patterned GaN(0001)/sapphire substrates by using the selective MOVPE technique. The dot-pattern is a hexagon arranged with a 5μm width and a 10μm spacing. The GaN structure comprises a hexagonal pyramid covered with six {11ȃ01} pyramidal facets on the side or a frustum of a hexagonal pyramid having a (0001) facet on the top. The facet formation mechanism has been investigated by observing the facet structure with the growth time. The {11ȃ01} facets are very stable during the growth. The (0001) facet growth is dominant at the initial growth but almost stops at a certain growth time and then the facet structure is maintained. The appearance of the self-limited (0001) facet is attributed to the balance of flux between incoming Ga atoms from the vapor phase to the (0001) surface and outgoing Ga atoms from the (0001) surface to the {11ȃ01} surface via migration. The longer the diffusion length of the Ga atoms on the (0001) surface is, the more the surface migration is enhanced, resulting in the appearance of the wider (0001) facet on the top.
New Buffer Layers for GaN on Sapphire by Atomic Layer and Molecular Stream Epitaxy
Authors: Piner E.L. , He Y.W. , Boutros K.S. , Mcintosh F.G. , Roberts J.C. , Bedair S.M. , El-Masry N.A.
Published: April 2011

The current approach of depositing a low temperature then annealed AlN or GaN buffer for the growth of GaN on sapphire results in a high dislocation density. These dislocations thread through the GaN layer to the surface. Reducing their density either by growing thicker films or using a strained layer superlattice is ineffective. Two new approaches for AlN/GaN buffer layer growth for GaN on sapphire have been employed: Atomic Layer Epitaxy (ALE) and Molecular Stream Epitaxy (MSE). ALE is distinguished by organo-metallic/ammonia separation while MSE is distinguished by cyclic annealing of the growing film. Both ALE and MSE enhance two dimensional growth of single crystal GaN on sapphire. The structural quality of epitaxial GaN grown on these buffer layers was studied by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The initial result for the ALE buffer shows an improved quality GaN film with lower defect densities. The MSE grown buffer layer closely resembles that of conventionally grown MOCVD buffer layers observed by others, with dislocations threading through the GaN epilayer. The effects of these buffer layers on the structural and optical properties of GaN grown on sapphire will be presented.
Epitaxial Growth of AlN Thin Films on Silicon and Sapphire by Pulsed Laser Deposition
Authors: Vispute R.D. , Wu H. , Jagannadham K. , Narayan J.
Published: April 2011

AIN thin films have been grown epitaxially on Si(111) and Al2O3(0001) substrates by pulsed laser deposition. These films were characterized by FTIR and UV-Visible, x-ray diffraction, high resolution transmission electron and scanning electron microscopy, and electrical resistivity. The films deposited on silicon and sapphire at 750-800°C and laser energy density of ∼ 2 to 3J/cm2 are epitaxial with an orientational relationship of AIN[0001]║ Si[111], AIN[2 110]║Si[011] and AlN[0001]║Al2O3[0001], AIN[1 2 1 0]║ Al2O3[0110] and AIN[1010] ║ Al2O3[2110]. The both AIN/Si and AIN/Al2O3 interfaces were found to be quite sharp without any indication of interfacial reactions. The absorption edge measured by UV-Visible spectroscopy for the epitaxial AIN film grown on sapphire was sharp and the band gap was found to be 6.1eV. The electrical resistivity of the films was about 5-6×l013Ω-cm with a breakdown field of 5×106V/cm. We also found that the films deposited at higher laser energy densities ≥10J/cm2 and lower temperatures ≤650°C were nitrogen deficient and containing free metallic aluminum which degrade the microstructural, electrical and optical properties of the AIN films
Hydrogen, Acceptors, and H-Acceptor Complexes in GaN
Authors: Bosin Andrea , Fiorentini Vincenzo , Vanderbilt David
Published: April 2011

We present ab-initio calculations on energetics and geometries of atomic hydrogen, of several candidate acceptors, and of H-acceptor complexes in wurtzite GaN For the H-Mg complex in Mg-doped GaN, we calculate the vibrational frequencies of H. Hydrogen is found to be a negative-U center. H-acceptor complex formation is always exothermic. Substitutional Be has a low formation energy and a shallow impurity level, which makes it a good candidate for p-doping in MBE growth. CN appears not to be shallow. Atomic hydrogen incorporation in undoped GaN is disfavored in an H2 atmosphere; it becomes favorable in p and n-type conditions in atomic H environments.
Properties of GaN Epitaxial Layer Grown by MOVPE on MgAl2O4 Substrate
Authors: Kuramata A. , Horino K. , Domen K. , Soejima R. , Sudo H. , Tanahashi T.
Published: April 2011

We propose a MgAl2O4 substrate for GaN-based laser diodes. We grew GaN epitaxial layers using metal-organic vapor phase epitaxy on a MgAl2O4 substrate. The GaN on the MgAl2O4 showed a narrow X-ray diffraction peak of 310 arcsec, a photoluminescence dominated by the band-edge emission, and good electronic properties. The optical cavity was fabricated by cleaving the GaN on the MgAl2O4, and the stimulated emission from the cavity using optical pumping was observed. We also fabricated a light emitting diode (LED) with a AlGaN/InGaN double-heterostructure. The electroluminescence was dominated by the band-edge emission of InGaN with a narrow FWHM of 13.5 nm. The characteristics of LED on the MgAl2O4 were comparable to that on a A12O3 substrate. MgAl2O4 is feasible as a substrate for laser applications.
Theory of Point Defects and Complexes in GaN
Authors: Neugebauer Jörg , Van de Walle Chris G.
Published: April 2011

We have studied the electronic and energetic properties of native defects, impurities and complexes in GaN applying state-of-the-art first-principles calculations. An analysis of the numerical results gives direct insight into defect concentrations and impurity solubility with respect to growth parameters (temperature, chemical potentials) and into the mechanisms limiting the doping levels in GaN. We show how compensation and passivation by native defects or impurities, solubility issues, and incorporation of dopants on other sites influence the acceptor doping levels. The role of hydrogen in enhancing the p-type doping is explained in detail. We also discuss the mechanisms responsible for the experimentally observed limitation of the free-carrier concentration in p-type GaN.
Electron cyclotron resonance etching characteristics of GaN in plasmas with and without hydrogen
Authors: Zhang L. , Ramer J. , Brown J. , Zheng K. , Lester L.F. , Hersee S.D.
Published: April 2011

Electron cyclotron resonance (ECR) plasma etching characteristics of gallium nitride (GaN) are investigated using low pressure (4-10 mTorr) SiCl4/Ar and Cl2/H2/Ar ECR discharges. The purpose of this effort is to develop a dry etching process for making laser mirrors on GaN and to examine dry etching processes of GaN that do not require hydrogen, which is known to cause carrier compensation in GaN. The etch rate is found to increase near-linearly with increasing DC bias, and a minimum DC bias of 100V is required to initiate etching in SiCl4/Ar. We have also found that the material quality significantly affects the etch rate. The latter decreases with x-ray rocking curve half-width and increases with defect density. A reasonable etch rate of 660Ǻ/min and good surface morphologies obtained in SiCl/Ar ECR etching make this process suitable for gate recess of an FET. An etch rate of 5270Ǻ/min has been achieved in Cl2/H2/Ar plasmas. This is the highest reported etch rate of GaN so far. The smooth and vertical etch sidewalls (etch to mask selectivity of 16 is obtained) make this process promising for dry-etched laser mirrors on GaN.
Properties of Zn Implanted GaN
Authors: Strite S. , Epperlein P. W. , Dommann A. , Rockett A. , Broom R. F.
Published: April 2011

We report the optical and structural properties of ion implanted GaN:Zn. Post-implant annealing up to 1100 °C was performed under flowing N2 in both a tube furnace and a rapid thermal annealing (RTA) system, with and without SiNx encapsulation layers. The implantation damage is quantified by transmission electron microscopy (TEM). Secondary ion mass spectroscopy (SIMS) detects significant rearrangement of implanted Zn only at the highest temperatures and doses investigated. Strain reduction, observed in GaN:Zn annealed at or above 975 °C by high-resolution x-ray diffractometry (HRXRD), indicates successful damage removal. The optical activation of annealed GaN:Zn is measured by photoluminescence (PL). The room temperature (RT) Zn acceptor transition at ∼430 nm is consistently observed in annealed GaN:Zn, but at low efficiency. We conclude that residual implantation damage and/or N loss during annealing limits the optical quality of implanted GaN:Zn.
Interfacial Reactions Between Metal Thin Films and p-GaN
Authors: Trexler J.T. , Miller S.J. , Holloway P.H. , Khan M.A.
Published: April 2011

The reactions between Au, Au/Ni and Au/C/Ni thin films on p-GaN have been studied using current-voltage (I-V) measurements, Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). The metallization schemes consisted of ≈2000Ǻ sputtered Au, 1000Ǻ Au/500Ǻ Ni, and 1000Ǻ Au/100Ǻ C/500Ǻ Ni electron beam evaporated. The Au/Ni metallization scheme is of particular interest since it is the basis for the most commonly used ohmic p-type contacts for blue GaN LED’s. Au does not decompose the GaN matrix, while Ni has been shown to react with GaN above a temperature of 400° C for times longer than 5 minutes. Upon decomposition of the GaN by Ni, incorporation of C at the metal/GaN interface occurred. It is believed that a regrowth of GaN occurred, with the surface region being doped with C. Attempts at increasing this doping concentration by introducing an interfacial C layer were not successful.
Metallurgical Study of Contacts to Gallium Nitride
Authors: Mohney S.E. , Luther B.P. , Jackson T.N. , Khan M.A.
Published: April 2011

Thermally stable contacts to GaN that also have desirable electrical characteristics are required for the further development of optoelectronic and high temperature devices based on GaN. To make improvements on existing contacts or to develop new ones, information on the metallurgy of potential contact systems is needed. In this work, the Metal-Ga-N ternary phase equilibria and the contact metallurgy are examined for Ti, Re, and Ni. Annealed contacts of these metals have been examined with x-ray diffraction and/or x-ray photoelectron spectroscopy, and the observed metallurgical reactions are discussed in light of estimated or experimentally determined Metal-Ga-N phase diagrams. Particular attention is paid to the gas phase equilibria and the role of the annealing environment on the metallurgical reactions. Finally, the consequences of this work for the design of thermally stable contacts are considered.
Pulsed Laser Deposition of ZnO: Energetic Rydberg State Atoms and Their Impact on Film Growth
Authors: Leuchtner Robert E.
Published: April 2011

A detailed comparison of the ZnO film microstructure prepared with both targets at two deposition pressures (0.01 and 0.1 torr) and a variety of substrate temperatures from 50-500°C was performed. The crystallographic and morphological results suggest that the condensation of highly electronically excited state particles, both ions and long-lived excited state neutrals likely affects film growth, and can enhance desirable surface processes, such as athermal recrystallizalion and surface mobility, that favor oriented crystal growth at lower substrate temperatures.
Excimer Laser Applications in Integrated Circuit Packaging
Authors: Lu Y. F. , Hong M. H. , Chan D. S. H. , Low T. S.
Published: April 2011

Excimer laser ablation is applied in the deflashing and demarking of IC packages. It is found that mold flash filled in the interface holes of IC leadframe can be removed completely by the laser deflashing in a short period of time. With appropriate selection of laser parameters, deflashing quality and efficiency can be greatly improved. The laser deflashing is more efficient for higher pin count packages. It is a superior alternative in future applications. In laser demarking, ink marks on package surfaces can also be removed completely in a short time. The surface after the processing has good conditions for remarking. The package remarking shows good permanency. The lifetime for good marking is much longer for IC packages after the laser demarking than those after hydrogen flame-off. Laser processing can be used to replace hydrogen flame-off in the ink printing of IC packages for high efficiency and safety.
On The Origin of Laser-Induced Surface Activation of Ceramics
Authors: Pedraza A.J. , Park J.W. , Lowndes D.H. , Cao S. , Allen W.R.
Published: April 2011

The surfaces of Al2O3and AlN are modified by pulsed-laser irradiation This modification promotes the deposition of copper when the irradiated substrates are immersed in an electroless bath. In this paper the nature of the surface modification is analyzed using results from Auger Emission Spectroscopy (AES) and Cross Sectional Transmission Electron Microscopy (XTEM). During irradiation AlN thermally decomposes leaving a discontinuous metallic film on the surface. A film of Al2O3is detected at the surface of the irradiated AlN substrate, much thicker when the irradiation is performed in an oxidizing atmosphere than when done in a reducing one. Nanoparticles of metallic aluminum are generated during laser irradiation of Al2O3in a reducing atmosphere. When the irradiation of Al2O3is performed in an oxidizing atmosphere, regions containing aluminum or substoichiometric alumina are detected by AES. It is concluded that the presence of metallic aluminum is the main reason why electroless deposition can occur in both AlN and Al2O3. Deposition kinetics are completely consistent with this conclusion. It is very likely that also substoichiometric alumina helps to catalyze the electroless deposition.
Excimer Laser Processing of Tool Steel: Tribological Effects of Multiple Pulse Processing and Ti Alloying
Authors: Jervis T. R. , Nastasi M. , Griffin A. J. , Zocco T. G. , Taylor T. N. , Foltyn S. R.
Published: April 2011

Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1,000 cycles, indicating wear-through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
Optimization of Bulk Hgcdte Growth in a Directional Solidification Furnace by Numerical Simulation
Authors: Bune A.V. , Gillies D.C. , Lehoczky S.L.
Published: April 2011

A numerical model of heat transfer by combined conduction, radiation and convection was developed using the FIDAP finite element code for NASA's Advanced Automated Directional Solidification Furnace (AADSF). The prediction of the temperature gradient in an ampoule with HgCdTe is a necessity for the evaluation of whether or not the temperature set points for furnace heaters and the details of cartridge design ensure optimal crystal growth conditions for this material and size of crystal. A prediction of crystal/melt interface shape and the flow patterns in HgCdTe are available using a separate complementary model.
Kinetics and Thermodynamics of the Formation of Thin Film Titanium Diselicide
Authors: Kasica R.J. , Cotts E.J. , Ahrens R.G.
Published: April 2011

Multilayered difiiision couples consisting of alternating layers of titanium (Ti) and amorphous silicon (a-Si) have been fabricated using sputter deposition with a range of modulation lengths corresponding to an average composition of Ti33 Si67. We have used differential scanning calorimetry to measure the enthalpy evolved during the solid state reaction a-Si + Ti → C49-TiSi2 and have characterized the phases formed using x-ray diffraction analysis. An average measured enthalpy of formation, ΔΗ was found to be ΔΗ = -58 + 9 kJ/g atom for thin film samples. Using scanning and isothermal calorimetry measurements, we have also characterized the kinetics involved during the initial intermixing stage.
Alloying in an Immiscible Cu-Nb System upon Solid-State Reaction
Authors: Pan F. , Ling Z.F. , Gao K.Y. , Liu B.X.
Published: April 2011

In an immiscible Cu-Nb system, an amorphous alloy and two metastable crystalline phases were obtained by solid-state reaction of Cu-Nb multilayered films, and the formation of the alloy phases was found to be quite sensitive to the average composition of the films. At Nb concentration of 75at%, amorphization was achieved by 250°C annealing for 50 min, while in the films with compositions of 70 and 80 at% Nb, a simple cubic (a=0.405±0.005nm) and an orthorhombic phase (a=0.421, b=0.334, c=0.291±0.005nm) were observed, respectively. Thermodynamic calculation was conducted for the Nb-Cu alloy phases and the energetic state of the multilayers, which consisted of 9 Cu/Nb bilayers. It turned out that the excess free energy originating from the interfacial atoms could raise the multilayers to an energy level being higher than that of the amorphous or/and metastable crystalline phases both with a convex shape, and thus provided a major driving force for alloy phase formation in such immiscible system.
Hydrogen Release and Si-N Bond-Healing Infrared Study of Rapid Thermal Annealed Amorphous Silicon Nitride Thin Films
Authors: Santos-Filho P. , Stevens G. , Lu Z. , Koh K. , Lucovsky G.
Published: April 2011

We address aspects of hydrogen bonding and its thermal evolution in amorphous Silicon nitride films grown by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD) from SiH4 and NH3 (or ND3) source gases. Rapid Thermal Annealing (RTA) decreases the Si-H(D) and SiN-H(D) bond populations. The hydrogen bonds break, and H2 (HD, D2) forms and evolves from the film with the heat treatment. This molecular hydrogen release is accompanied by Si- and N- bond healing as detected by a SiN infra red stretch mode signal gain. The ex-situ RTA experiment temperatures ranged from 400 °C to 1200 °C, in 100 °C steps and the film structural changes were monitored by Fourier Transform Infrared spectroscopy (FTIR) after each incremental anneal. Gas flow ratios R=NH3/SiH4 > 2 produced films in which SiN-H(D) bonds dissociated, and a gas desorption rate equation estimated an activation energy barrier of Ea = 0.3 eV. The release of hydrogen from the films in the form of H2 (D2) and ammonia radicals was detected by mass spectrometry and is shown here. The re-bonding of nitrogen to silicon upon thermal dissociation of hydrogen's is consistent with the improvement of the electrical properties of a-SiN:H films following RTA treatment.
In Situ Study of the Temperature Dependence of Irradiation-Induced Amorphization in A-Sic
Authors: Weber W. J. , Wang L. M. , Yu N. , Hess N. J.
Published: April 2011

Ion-beam-induced amorphization in single crystal α-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar+ ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe+ irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.
The Crystal-Melt Interface in Si or Ge
Authors: Spaepen Frans , Shao Yan
Published: April 2011

From the nucleation data on undercooling of liquid Si or Ge, crystal-melt interfacial tensions are calculated. Only a temperature-dependent tension can account simultaneously for the results of experiments on bulk and thin film Si. The observed temperature dependence can be accounted for by reasonable values of the interfacial entropy and enthalpy. The analysis is used to determine the temperature-dependent interfacial tension for Ge. A comparison of results for Ge and Si indicates that homogeneous nucleation has not been achieved in the undercooling of bulk liquid Si.