bluuebunny/crossref_metadata_2025 huggingface dataset:
Material and Reliability Considerations for Anisotropically Conductive Adhesive Based Interconnects
Authors: Dion J. , Borgesen P. , Yost B. , Lilienfeld D. A. , Li C.-Y.
Published: March 2011

An adhesive based interconnect design in which the contact force between a bumped die and substrate is maintained by the shrinkage stress of the adhesive was investigated for use in high performance applications. In general, heating will reduce the contact force because of the differential thermal expansions and load relaxation in the adhesive. Special experimental techniques have been developed to measure the relevant materials properties. The potential for optimization in terms of materials selection is discussed.
High Temperature Polyimide Nanofoams
Authors: Charlier Y. , Russell T. P. , Hedrick J. L.
Published: March 2011

A means of generating high temperature polymer foams which leads to pore size in the nanometer regime has been developed. Nanofoams were prepared by casting block copolymers comprised of a thermally stable block and a thermally labile material, where the thermally stable material forms the matrix in which thermally labile material is dispersed. Triblock copolymers comprised of high Tg, amorphous polyimide matrices with poly(propylene oxide), as the thermally decomposable coblock, were prepared. The copolymer synthesis was carried out through either the poly(amic alkyl ester) or poly(amic acid) precursor and subsequent cyclodehydration to the polyimide by either thermal or chemical means, respectively. Microphase separated morphologies were observed for all copolymers, irrespective of the block lengths surveyed, by dynamic mechanical analysis. Upon heating, the poly(propylene oxide) underwent thermolysis leaving pores where the size and shape of the pores were dictated by the initial copolymer morphology. A 5 to 15% reduction in density was observed consistent with the generation of a foam.
Electrical Characterization of Low Dielectric Constant LCP Composite Films
Authors: Walpita L. M. , Lundberg G. , Stamatoff J.
Published: March 2011

A variety of low dielectric constant composites have been made into films and characterized. These composites were blends of liquid crystalline polymers (LCPs), hollow glass spheres (HGS) and polytetrafluoroethylene (PTFE). By adjusting the percentage compositions of the various components of the composites, the dielectric constant could be adjusted in the range 2.4 to 3.4. Measurement of the dielectric constant by Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR) are discussed. Dielectric anisotropy is also discussed. The experimentally observed results are compared with those derived theoretically.
Moisture Absorption and its Effects on the Performance of Printed Circuit Materials
Authors: Liu P. C. , Wang D. W. , Fuerniss S. J. , Poliks M. D. , Obrzut J. , Siperko L. M. , Chen W. T. , Havens R. D. , Murcko R. M.
Published: March 2011

Polymers have found wide usage in microelectronics industry. Their moisture absorption properties cause the concern of reliability without hermeticity (RwoH). For printed circuit packages, the lamination process, the components assembly, and the field performance of final product are strongly influenced by the presence of high level moisture content. For instance, moisture is an important factor in the development of internal shorts through metal migration when printed circuit package is in service. Moisture can also cause dimensional changes in printed circuit cores and delamination during the soldering processes in components assembly, resulting in manufacturing yield loss and defects. Understanding moisture properties of resins and the resin glass composites are therefore important in developing a strategy to control the moisture content of final products. This paper will discuss the moisture fundamental properties of two resins and their resin glass systems. These properties will be related to their assembly and reliability performance.
Factors Affecting Metal/Polymer Interface Durability in Microelectronics Packaging: Chemistry and Water Uptake
Authors: Clearfleld H. M. , Furman B. K. , Callegari A. , Graham T. , Purushothaman S.
Published: March 2011

Durability of metal/polymer interfaces is essential for the long-term reliability of high performance microelectronics packages. Such interfaces undergo stresses during production and in service. In this work, we report on the durability of interfaces formed between reactive metals and polyimides (PI) that have been subjected to stresses simulating both types of environment. The P1 surfaces were treated by Ar RF plasmas prior to metal deposition, and durability was determined by measuring the 90 degree peel strength as a function of environmental exposure. The durability of Cr and Ti/PMDA-ODA interfaces through processing stresses (i.e., large thermal excursions) depends on the PI surface modification and the metal reactivity. For both, we observed interfacial degradation due to oxidation of the metal–the cause is water absorbed by the polyimide. These studies, coupled with water transport measurements, suggest that the physical structure of the interface is the dominant factor. To determine the durability under service environmental stresses (e.g., temperature/humidity), we correlated peel strengths with interfacial chemistry and water uptake. In this case, Ar and O2plasmas were used. For Ta/BPDA-PDA, the durability depends on the type of plasma treatment. Ar-treated specimens maintain strength through 500 hours T/H stressing whereas those treated by O2plasma alone fail at 165 hours. The differences here can be explained by the interfacial chemistry–Ta/Ar-etched surfaces form a stable TaG-like structure whereas the Ta/O2-etched surfaces form a metastable, sub-oxide structure that transforms to Ta2O5during stressing. Ta/PMDA-ODA interfaces fail readily under these conditions due to the increased water uptake of the PI.
Investigations of Curing Chemistry and Hydrolytic Stability of Polyimide - on - Metal Interfaces
Authors: Cumpston B. H. , Nagarkar P. V. , Cornella G. , Volfson D. , Trusell F. , Jensen K. F. , Senturia S. D.
Published: March 2011

Polyimide-on-metal interfaces relevant to electronics packaging applications have been studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Two polyimides with different backbone structures were considered: (i) biphenyltetracarboxylic dianhydride (BPDA) - p-phenylene diamine (PDA) and (ii) 4,4′-(hexafluroisopropylidene)-bis(phthalic anhydride) (6FDA) - 4,4′-bis(4-aminophenoxy) biphenyl (APBP). Thin polymer films (10–100 nm) were cured on Al, Cr and Cu surfaces at different temperatures to allow probing of chemical interactions by surface spectroscopies. Anhydride intermediates were detected on all three substrates for both polyimides. Carboxylate intermediates were detected in BPDA-PDA films on Cr and Cu and resulted in increased adhesion at these interfaces. XPS data revealed a nitrogen deficiency at the BPDAPDA/Cr interface. A mechanism explaining the formation of this intermediate and the deficiency of nitrogen is proposed. Hydrolytic stability of the interface was investigated using ex situ total internal reflection FTIR spectroscopy and XPS. The results show that the fluorinated polyimide, 6FDA-APBP, is more stable than BPDA-PDA when treated at 85 °C and 85% relative humidity for 100 hours.
Theoretical Modelling of Polymer Metallization: an Assessment of Bonding Mechanisms that Effect the Formation of Stable Metal Overlayers
Authors: Jansen S. , Palmieri M. , Grabania S. , Whitwell G.
Published: March 2011

In this work, we present a systematic approach to the problems in polymer metallization. There are three main components to our study which include: assessment of the limits of metal polymer interaction, consideration of metal-metal interaction or aggregration at the interface limit, and modification of the copper surfaces to increase reactivity. All of these phenomena are assessed through application of semi-empirical electronic structure calculations with the ultimate objective being to effect a strategy for better metal deposition with the primary metal being copper. Polymer models include polyimide, epoxy resins, polyolefin ketones, and nitrile functionalized polymers. In the first component study, orbital interactions which affect adhesion are compared for a variety of polymer models and transition metals. This initial study is then extended to consider the potential for metallization by consideration of competition of metal-polymer interactions and metal-metal interactions as a metal lattice “grows” at the metal/polymer interface. Finally modification of the metal/polymer interface is assessed by considering the effect of oxidation or codeposition of dissimilar metals to augment the electronic properties and thus affinity of copper for the polymer. The general trends produced in this work are consistent with experimental measurements of adhesion and have been validated by spectral measurements. This work clearly shows the molecular level limitations of polymer-metal interactions for a series of important systems.
An Adhesion Study of Copper and Chromium Films to Polyimide
Authors: Chung T. G. , Yu Jin , Kim Y.-H. , Ahn E. C. , Park I. S.
Published: March 2011

Adhesion of Cu and Cr to polyimide was studied by 90° peel test, AES, and X-ray diffraction. The two necessary conditions of the high adhesion strength were the presence of Cr interlayer and the preactivation of the polymer surface by RF plasma treatment. The Cr is thought to react with activated polyimide to form carbide-like bonds which enhance the adhesion strength drastically. Correlations between the peel strength and C260/Cr527 Auger PHR from the peeled metal strip were good. Qualitatively, the peel strength is related to the amount of plastic deformation done on the metal strip during peeling.
Micromechanical Testing of Electronic Packaging Components and Materials
Authors: Li C.-Y. , Yost B. , Korhonen M. A. , Dion J.
Published: March 2011

Mechanical modelling of microelectronic packages for design optimization requires the quantitative knowledge of a large number of physical parameters. Because of the composite nature of many components, and because relevant materials properties in the microscale often deviate from the bulk values, there is therefore a need for a variety of micromechanical testing techniques. These techniques include tension, compression, shear, bending, and fatigue testing of samples with sizes in the 10 micron range. A novel technique has been developed for the testing the z-direction properties of thin films with displacements in the sub-micron range. Mechanical properties of thin films and surface regions may advantageously be probed by a continuous microindentation tester. All elastic properties of both isotropic and anisotropic packaging materials and components may be evaluated directly by the above methods, and the inelastic deformation behavior determined over many orders of magnitude of strain rate by load relaxation measurements. The above techniques and examples of their application will be discussed.
Mechanical and Accelerated Testing of Flip Chip Interconnect Systems
Authors: Subrahmanyan Ravi
Published: March 2011

Flip chip interconnect systems are becoming increasingly popular in the electronics industry due to their low profile and high densities. During temperature cycles, the differential expansions between various assembly members of a flip chip interconnect system produce mechanical stresses that are the driving force for failures. Such failures can be a significant reliability concern.

Accelerated test methodologies for flip chip interconnect systems assess the reliability of existing interconnects and identify potential reliability concerns in future interconnect designs. Traditionally, such methodologies have relied on test methods such as temperature cycling to determine the mechanical integrity of the flip chip interconnect. However, application of such methods to new interconnect materials, geometry and processes requires characterization of basicmechanical behavior of the interconnect system.

In this work, the feasibility of using a micromechanical test methodology for flip chip applications is examined. 90PbSn solders is used as an example. The data obtained from such flip chip solder interconnects is validated using a damage integral methodology. The measured data is shown to adequately describe published thermal stress profiles and thermal fatigue life data measured using solder joints of the same composition. Finally, some considerations in the application of micromechanical measurements to determination of acceleration factors and development of accelerated test methods are discussed.
Characterization of Mems Actuators Via Nanoindentation
Authors: Glumac D. E. , Rizq R. N. , Robbins W. P. , Polla D. L. , Nelson J. C.
Published: March 2011

Nanoindentation has been used to characterize polycrystalline silicon serpentine structures which will become the “framework” for piezoelectric meander line microactuators. These structures are fabricated using silicon wafer surface micromachining processing techniques, and they are suspended about 1 micron above the wafer surface. Normally, nanoindentation equipment is used for materials scratch-testing; however, this equipment was modified so that a probe tip could make contact to the sides of the meander lines, thus enabling known forces to be applied parallel to the wafer surface. For one type of device, the nanoindentaion technique yielded a spring constant of 400 N/m, while simple beam theory gave 1300 N/m and the finite element analysis software ANSYS gave 1200 N/m. This measurement technique holds the promise of being able to apply a known force and then countering that force with piezoelectric actuation to determine the forces that future piezoelectric microactuators will be able to provide.
Determination of Shear Stress at a Solder Paste/Stencil Interface
Authors: Head Linda M. , Rogers Vincent , Sahay Chitteranjan , Constable James
Published: March 2011

To create a model for the release process of solder paste during stencil printing for surface mount applications it is necessary to determine the shear stress developed at the interface between the solder paste and stencil sidewall. An experiment has been developed to determine the value of the shear stress for solder paste samples. For the purpose of this experiment a Micro-mechanical tester has been adapted and programmed to provide both a shear thinning cycle and a pull-off cycle that simulate aperture fill and stencil lift-off. The shear stress developed at the solder/stencil-sidewall interface is estimated from the data obtained during the pull-off portion of the Micro-mechanical test procedure. The micro-mechanical tester is fitted with a set of parallel plates that can be adjusted for plate separation and surface roughness.

The experiment consists of two parts: (1) the shear thinning cycle and (2) the horizontal pull-off. After application of the solder paste and adjustment of plate separation, a back and forth movement of the upper plate provides shear thinning of the paste. This step is necessary to simulate the shear thinning that occurs from the application of squeege pressure during aperture fill. The horizontal pull-off then simulates the lift-off step of the stencil printing procedure. During the horizontal pull-off data is. taken which allows calculation of the force developed as the upper plate is pulled away from the lower. Results from this experiment show the values of shear stress that develop during pull-off with a variation of surface treatments and plate separations.

This paper will present the experimental set-up, a description of the relationship between this experiment and the actual stencil lift-off process, and shear stress data that has been acquired for a variety of solder pastes and plate separations.
The Use of Gravure Offset Printing in the Realisation of Fine Line Thick Film Conductors
Authors: LeppÄvuori S. , VÄÄnÄnen J. , Lahti M. , Kukkola K. , UusimÄki A.
Published: March 2011

The use of gravure offset printing to transfer film patterns from an inked plate to the substrate by a silicone rubber pad has been shown to have promising advantages in fine line and multilayer production. The technology is now moving into the field of electronics manufacturing. By optimising the printing parameters and ink characteristics in the gravure offset technique, lines and spaces as narrow as 50 μtm were achieved and even finer lines are possible. Commercially available fine line thick film Au and Ag pastes were modified for this purpose. The thickness of sintered conductors ranged from about 2 to 11 μtm depending on ink viscosity, control of printing equipment and repetition of prints. When compared with films deposited by conventional thick film technology, the conductivity and adhesion on alumina were similr. The small interconnections between conductors through the insulator layer necessary in multilayer techniques were realised using gravure offset printing to coat excimer laser drilled vias. Interconnection diameters of less than 100 μtm were achieved.
In situ and Ex situ Applications of Spectroscopic Ellipsometry
Authors: Woollam John A. , Johs Blaine , McGahan William A. , Snyder Paul G. , Hale Jeffrey , Yao Huade Walter
Published: March 2011

We briefly review the optics of ellipsometry, followed by discussions of a series of example applications of the technique including single films on a substrate; multilayer stacks common to silicon integrated circuit fabrication; flat panel display materials, and in situ semiconductor growth and deposition control.
In-Situ Diagnostics of Plasma-Induced Damage on GaAs by Photoreflectance Spectroscopy
Authors: Nakanishi Hideo , Wada Kazumi
Published: March 2011

Photoreflectance spectroscopy (PR) is used to make in-situ diagnostics of subsurface damage behavior during Ar-plasma etching of n-type GaAs. The diagnostics in-situ PR first unveil anomalous damage behavior at an early stage of plasma etch- ing: Franz-Kerdysh oscillation shows an abrupt decrease in the surface electric-field strength from 130 to 30 kV/cm within 10 sec. This indicates that acceptor-like defects with a concentration of more than 1 × 1017cm−3 are created at the very beginning of the plasma etching. The δR/R abruptly decreased to 4% in intensity upon within 5 sec. of plasma etching and subsequently recovered. This indicates that recombination centers are quickly introduced, then further plasma etching gradually removes such centers, possibly by etching the damaged layer. Photoluminescence (PL) intensity decreases to 72% but does not show any recovery, indicating that PL is dominated by recombination centers in a deeper region. Thus, in-situ PR diagnostics is the first method to provide detailed findings on new damage behavior during Ar-lasma etching.
Layered Semiconductor Photoreflectance Diagnostics
Authors: Boltar Konstantin.O. , Fedirko Valery.A.
Published: March 2011

We have investigated IR reflectance spectra of semiconductor structures consisting of up to 5 epitaxial GaAs/GaAlAs layers on GaAs wafer, diffused and implanted profiles in Si wafers to find the semiconductor structures parameters.
Characterization of Pseudomorphic Hemt Structures by Modulation Spectroscopy
Authors: Dimoulas A. , Zekentes K. , Androulidaki M.
Published: March 2011

Phototransmittance has been used to investigate several pseudomorphic Al0.32Ga0.68As/In0.15Ga0.85As/GaAs high electron mobility transistor structures, with different values of the electron density ns. A lineshape analysis of the ground state transition made it possible to estimate ns, at room temperature. A signal from the Fermi-edge singularity (a manybody effect), was observed at low temperatures and the dependence of its intensity on temperature and electron density was examined.
Optical Characterization of AlInP/GaAs Heterostructures
Authors: Johnson F.G. , Kohnke G.E. , Wicks G.W.
Published: March 2011

A 45 period GaAs/A10.54In0.46P superlattice was grown by molecular beam epitaxy using valved solid-sources to supply both the arsenic (As4) and the phosphorus (P2) group V fluxes. The room temperature optical transmission spectrum shows evidence of ground state excitons. Higher energy confined states are exhibited in photovoltage and photoreflectance spectra. Doublets corresponding to the m≈1 through m≈7 folded longitudinal-acoustic phonon modes are observed in the Raman spectrum. Analysis of these phonon doublets enables the structure of the superlattice to be determined. The interface roughness was found to be approximately 2 monolayers, and the layer thicknesses were determined to be 82 Å GaAs and 48 Å A10.54In0.46P.
In-Process Diagnostic System for Semiconductor Materials Using UHV Wafer Transfer Chamber
Authors: Uchida F. , Matsui M. , Kakibayashi H. , Kouguchi M. , Mutoh A. , Nagano H.
Published: March 2011

We have developed a novel stand-alone diagnostic system that can analyze a semiconductor wafer surface in each process without introducing contamination. This allows us to analyze the relationship between chemical conditions and device properties.

A UHV (Ultra High Vacuum) wafer transfer chamber is used between the measuring apparatus and the semiconductor processes. The chamber vacuum system, which consists of a battery driven ion pump and a liquid N2 shroud, achieves a pressure of 2 × 10−8 Pa (corresponding to about 100 min. until one monolayer of contamination has been adsorbed).

Wafer transfer lines have been constructed between semiconductor vacuum processes, CVD (Chemical Vapor Deposition) and measuring instruments, ESCA (Electron Spectroscopy for Chemical Analysis) and TEM (Transmission Electron Microscope). Our results from ESCA and TEM showed measurements that carbon contamination and oxidation was suppressed.
Simultaneous Real Time Spectroscopic Ellipsometry and Reflectance for Monitoring Semiconductor and Thin Film Preparation
Authors: An Ilsin , Nguyen Hien V. , Heyd A. R. , Collins R. W.
Published: March 2011

This paper describes an expansion of the capabilities of real time spectroscopic ellipsometry (SE) that results from simultaneous measurement of a reflectance spectrum RA along with the two spectra in the ellipsometric angles (Ψ,δ). RA provides information complementary to (Ψ,δ), but until now has not been exploited in real time spectroscopic applications. Earlier, we have developed a novel rotating-polarizer multichannel ellipsometer for real time studies of thin film growth that utilizes a photodiode array (PDA) detector for highspeed acquisition of (Ψ,δ) spectra. Employing this instrument with a 12.5 Hz polarizer rotation rate, three-parameter (3-p) data sets {Ψ(hv,t), δ(hv,t), RA(hv,t); 1.4≤hv≤4.5 eV} can now be obtained with a time resolution as short as 40 ms during film growth. A resilient new analysis approach based on mathematical inversion and least-squares fitting is described to interpret the 3-p data set. The 3-p approach has been successful in characterizing plasmaenhanced chemical vapor deposition (PECVD) of amorphous semiconductors, and provides the film dielectric functions and thicknesses independently at each time during film growth. RA(hV) exhibits deviations from the spectrum predicted in successful modeling of (Ψ,δ) spectra alone. These deviations result from diffuse light scattering by particulates in the plasma. We show how additional information can be extracted from the spectral dependence of the scattering loss.
Single Photon Laser Ionization as an In-Situ Diagnostic for MBE Growth
Authors: Alstrin April L. , Kunz Adina K. , Strupp Paul G. , Leone Stephen R.
Published: March 2011

Single photon laser ionization time-of-flight mass spectroscopy (SPI-TOFMS) is used to monitor the gaseous fluxes of Ga and Asn, during molecular beam epitaxy of GaAs. This noninvasive and real-time probe measures densities, and hence fluxes, of multiple chemical species impinging on or scattered from a substrate during conventional MBE. With single photon ionization at 118 nm (10.5 eV, ninth harmonic of Nd:YAG laser), the photon energy is large enough to ionize the species, but insufficient to both ionize and fragment. The lack of molecular dissociation of As2 and As4 greatly simplifies the interpretation of mass spectra. Additionally, the geometry of the single photon ionization TOFMS permits simultaneous film growth monitoring using RHEED. Results will be presented on the probing of scattering and desorption of III-V MBE species during GaAs growth. This technique promises to be a valuable in-situ diagnostic for III-V and II-VI MBE.
Deep–Level Transient Spectroscopy Studies of Czochralski–Grown N–Type Silicon
Authors: Tokuda Yutaka , Katoh Isao , Katayama Masayuki , Hattori Tadasi
Published: March 2011

Electron traps in Czochralski–grown n-type (100) silicon with and without donor annihilation annealing have been studied by deep–level transient spectroscopy. A total of eight electron traps are observed in the concentration range 1010 –1011 cm −3. It is thought that these are grown–in defects during crystal growth cooling period including donor annihilation annealing. It is suggested that two electron traps labelled A2 (Ec–0.34 eV) and A3 (Ec–0.38 eV) of these traps are correlated with oxygen–related defects. It is shown that traps A2 and A3 are formed around 400 ° C and disappear around 500–600 ° C.
Study of Silicon Surface Roughness by Atomic Force Microscopy
Authors: Gilicinski Andrew G. , Rynders Rebecca M. , Beck Scotjt E. , Strausser Yale E. , Stets James R. , Felker Brian S. , Bohling David A.
Published: March 2011

Progress is reported in developing reliable methodology for imaging silicon surfaces with the atomic force microscope (AFM). A new form of AFM, known as tapping mode AFM, has been found to provide the best quality data for surface roughness determinations. Commercially available colloidal gold spheres have been used to fabricate tip characterization standards and are used to report tip size with roughness data. Power spectral density calculations are shown to provide a useful roughness calculation based on lateral wavelength.
The Effect of Polysilicon Deposition and Doping Processes on Double-Poly Capacitors - Electrical and AFM Evaluation
Authors: Paulson W. M. , Breaux L. H. , Hegde R. I. , Tobin P. J.
Published: March 2011

We have characterized the surface topography of silicon films from different deposition and doping process sequences using AFM and optical reflectivity. The resulting surface structures after deposition, doping, oxide growth, and oxide removal correlate with the electrical leakage currents and breakdown voltages of double polysilicon capacitors. As-deposited amorphous films had smoother surfaces than those deposited in the crystalline state. Gas-phase diffusion doping increases the surface roughness. Only the amorphous in situ doped films retained a smooth surface following oxidation, yielding low leakage capacitors with breakdown fields above 8 MV/cm. Surprisingly, implanted amorphous films exhibited the roughest interfaces, resulting in lower breakdown fields. This study has shown that AFM provides an effective, quick, non-destructive diagnostic technique for semiconductor processing.
The Performance Study of Ion Implanter Based Medium Energy Ion Spectroscopy with Solid State Detector
Authors: Radzimski Z. J. , Yokoyama S. , Ishibashi K. , Hirose M.
Published: March 2011

Medium-energy ion spectroscopy using a conventional ion implanter has been developed to study the properties of semiconductor subsurface regions. The system is equipped with solid state detector and operaties with He+ ion energy up to 200 keV. We have tested the system performance for various applications, such as, silicon diffusion through a thin Au layer, a low dose, low energy As implantion and damage of silicon surface caused by plasma treatment.
Semi-Insulating Behavior of Undoped Inp
Authors: Kainosho K. , Oda O. , Hirt G. , MÜller G.
Published: March 2011

Recently, it was found that semi-insulating behavior of undoped InP can be realized by high pressure annealing of undoped high purity InP. In the present work, studies related with the achievement of the semi-insulating state are reviewed. Purification of raw materials, effect of native defects, effect of high pressure annealing, contamination of Fe are discussed. The semi-insulation mechanism is explained by the Shockley diagram. The semi-insulating state is supposed to be achieved by the annihilation of shallow donors (presumably phosphorus vacancies) and the compensation of the residual donors with a small amount of Fe deep acceptor.
Strong Visible Photoluminescence in Silicon Nitride thin Films Deposited at High Rates
Authors: Deshpande Sadanand V. , Gulari Erdogan , Brown Steven W. , Rand S.C.
Published: March 2011

Amorphous silicon nitrogen alloy (a-Si:Nx) thin films have been deposited using a novel hot filament chemical vapor deposition (HFCVD) technique. In this method, a hot tungsten filament is used to decompose ammonia to obtain highly reactive nitrogen precursor species which further react with disilane to form silicon nitride thin films. This allows for very high deposition rates ranging from 600 Å/min to 2500 Å/min at low substrate temperatures. These films deposited at high rates show strong photoluminescence (PL) at room temperature in the visible region when excited with the 457 nm line of Ar+ ion laser. Intrinsic defects introduced into the amorphous silicon nitride matrix due to the rapid deposition rates seem to give rise to the visible PL. The PL intensity is at least 8-10 times stronger than silicon nitride films deposited by conventional plasma enhanced CVD. PL peak position of this broad luminescence was varied in the visible region by changing the film stoichiometry (Si/N ratio). The PL peak energy also scales predictably with the refractive index and optical band gap of the films. These samples showed reversible PL fatigue and also have band edge tail states characteristic of amorphous materials.
Effect of Pressure on Arsenic Diffusion in Germanium
Authors: Mitha S. , Theiss S. D. , Aziz M. J. , Schiferl D. , Poker D. B.
Published: March 2011

We report preliminary results of a study of the activation volume for diffusion of arsenic in germanium. High-temperature high-pressure anneals were performed in a liquid argon pressure medium in a diamond anvil cell capable of reaching 5 GPa and 7500 C, which is externally heated for uniform and repeatable temperature profiles. The broadening of an ion-implanted arsenic profile was measured by Secondary Ion Mass Spectrometry. Hydrostatic pressure retards the diffusivity at 575°C, characterized by an activation volume that is +15% of the atomic volume of Ge. Implications for diffusion mechanisms are discussed.
Recent Developments in Doping Techniques for Compound Semiconductors
Authors: Cunningham J. E. , Tsang W. T.
Published: March 2011

We report new methods to dope compound semiconductors. First, we demonstrate the concept of doping engineering whereby it becomes possible to tailor the activation energy of the dopant in a host semiconductor for the first time. In this application, the band offset of a thin, sacrificial semiconductor is used to lower the activation energy of the dopant below its value in the host semiconductor. This allows the freedom to control dopant activity in ways not accessible to a uniformly placed dopant. We chose δ-Be-AlGaAs/GaAs as a model example and show the hole binding energy is reduced by a factor of five. Secondly, we demonstrate overcoming the p-type solubility limit in GaAs by use of monolayer δ-Be in a GaAs base of an HBT. Here, an effective hole concentration of > 1021cm−3 is measured in real devices. We present a qualatative view of doping solubility limitations that are controlled by surface processes.
Annealing Effect on Photoluminescence Properties of Be-Doped MBE GaAs
Authors: Shibata Hajime , Makita Yunosuke , Yamada Akimasa
Published: March 2011

Low temperature (2° K) photoluminescence (PL) measurements were performed for the wavelength (λ) region from 800 to 1600 nm on Be–doped GaAs grown by molecular beam epitaxy (MBE) for wide range of net hole concentration at room temperature (p) up to 2 x 1020 cm−3 after annealing at 850 °C for 20 minutes. The annealing procedure formed several new PL emission bands associated with deep levels appeared between 0.4 and 1.4 eV. The most intensive new PL band appeared at around 1.2 eV with a band width of about 0.2 eV for all samples investigated. Its peak position and band width were observed to shift slightly toward lower energy side and increase, respectively with increasing p. An additional two sharp bands appeared overlapping the main band at around 1.31 and 1.35 eV for p less than 1 x 1018 cm−3. New broad band formation was also observed at around 1.0 eV in the same samples. In addition, a new prominent PL band was found at about 1.35 eV in the as-grown samples with p = 5 ∼ 6 x 1017 cm−3, which disappeared entirely after annealing. The formation and annihilation mechanism of these deep levels after annealing can be presumably attributed to Be redistribution from Ga sites to As sites and interstitial sites to Ga or As sites, driven by the formation of As vacancies (V As) due to As evaporation from samples during annealing.
Oxygen Doping of GaAs During Omvpe Controlled Introduction of Impurity Complexes
Authors: Park Y. , Skowronski M. , Rosseel T.S. , Manasreh M.O.
Published: March 2011

GaAs epilayers have been grown by Organo-Metallic Vapor Phase Epitaxy using dimethylaluminum methoxide as a dopant source. This compound contains a strong aluminumoxygen bond which is thought to remain intact during low temperature deposition and result in the incorporation of Al-O as a complex. Incorporation of aluminum and oxygen was investigated by Secondary Ion Mass Spectroscopy as a function of growth conditions: growth temperature, growth rate, V/III ratio, reactor pressure and dopant mole fraction. High doping levels up to 1020 cm−3 (for both oxygen and aluminum) were achieved without degradation of surface morphology andlor precipitation of a second phase. Oxygen concentration is lower than that of aluminum for all investigated growth conditions but at low deposition temperatures oxygen/aluminum ratios approach 1, indicating that Al-O is incorporated as a pair. Infrared absorption measurements in the 600-1200 cm−1 range did not detect well known isolated oxygen localized vibrational modes (LVM). Also in layers grown at low temperatures the intensity of isolated aluminum LVM at 362 cm−1 is much smaller than the concentration obtained by SIMS. Both observations prove that oxygen not only is incorporated as an Al-O pair but remains bonded in the bulk of the layer. Low temperature photoluminescence measurements indicate that the A1-O complex is electrically active in GaAs, forms a deep level within the GaAs band gap, and serves as an efficient non-radiative recombination center. Near band edge luminescence intensity correlates well incorporation of oxygen. The Al-O pairs act as deep acceptors in GaAs and cause the compensation of shallow tellurium donors.
Identification of Diffusion Associated Defects at III-V Semiconductor Heterostructures
Authors: Viturro R. Enrique , Wicks Gary W.
Published: March 2011

Cathodoluminescence spectroscopy is used to identify diffusion-associated III-V semiconductor defects and establish their role in AlGaAs/GaAs intrinsic and n-type impurity induced interdiffusion (Si, Ge, S, and Se) for various ambient conditions, As- and Ga-rich. These identifications involves the study of the temperature and composition dependence of these deep levels and their correlation with theoretical calculations. Our results reveal Column III vacancies and their complexes as the sole mediators of diffusion.
Proton Irradiation Damage in Zn and Cd Doped InP
Authors: Rybicki George C. , Williams Wendell S.
Published: March 2011

Deep Level Transient Spectroscopy (DLTS) was used to study the defects introduced in Zn and Cd doped Schottky barrier diodes by 2 MeV proton irradiation. The defects H3, H4 and H5 were observed in lightly Zn doped InP, while only the defects H3 and H5 were observed in more heavily Zn doped and Cd doped InP. The defect activation energies and capture cross sections did not vary between the Zn and Cd doped InP.

The concentration of the radiation induced defects was also measured. The introduction rate of the defect H4 in the lightly Zn doped InP and the introduction rate of the defect H3 in the heavily Zn and Cd doped InP were about equal, but the introduction rate of the defect H5 varied strongly among the three types of material. The introduction rate of H5 was highest in the heavily Zn doped InP but the lowest in the heavily Cd doped InP, even though they were doped comparably. As a result, the total defect introduction rate was lowest in the highly Cd doped InP.

The results can be interpreted in terms of the models for the formation and annealing of defects, and by the different diffusion rates of Zn and Cd in InP.
Vacancy Injection Enhanced Al-Ga Inter-diffusion in Si FIB Implanted Superlattice
Authors: Chen P. , Steckl A.J.
Published: March 2011

The Al-Ga inter-diffusion induced by Si FIB implantation and subsequent RTA were investigated in an Al0.3Ga0.7As/GaAs superlattice with equal 3.5 nm barrier and well widths. Si++ was accelerated to 50 kV as well as 100kV and implanted parallel to sample normal at doses ranging from 1013 to 1015/cm2. The effect of rapid thermal anneal of 10s at 950°C was characterized by SIMS technique. In the implanted region, the inter-diffusion as well as compositional mixing were significantly enhanced. An ion dose as low as 1×1014/cm2 results in a two-order of magnitude increase in the inter-diffusion coefficient, to a value of 4.5×10-14 cm2/sec, in contrast to 1.3×10-16 cm2/sec from RTA-only. This produces a mixing parameter of σ90%. A strong depth dependence of the mixing process was observed at implantation energy of 100keV with a pinch-off region being formed at certain depth. It is noticed that the depth where this enhancement occurred is not associated with either the maximum concentration of Si ions or of vacancies. Instead, it represents the positive maximum of the second derivative of the vacancy profile, which in turn represents the vacancy injection generated by presence of a transient vacancy concentration gradient. Based on this, a theoretical model was developed using vacancy injection as responsible for mixing.
Improvement of the Structural Quality of GaAs Layers Grown on Si with LT-GaAs Intermediate Layer
Authors: Weber Zuzanna Liliental , Fujioka H. , Sohn H. , Weber E.R.
Published: March 2011

Superior electrical and optical quality of GaAs grown on Si with an inserted low-temperature (LT)-GaAs buffer-layer was demonstrated. Photoluminescence intensity was increasing and leakage current of Schottky diodes build on such a structure was decreasing by few orders of magnitude. These observations were correlated with structural studies employing classical and high-resolution transmission electron microscopy (TEM). Bending of the threading dislocations and their interaction was observed at the interface between a cap GaAs layer and the LT-GaAs layer. This dislocation interaction results in the reduction of dislocation density by at least one order of magnitude or more compared for the GaAs layers with the same thickness grown on Si. The surface morphology of the cap GaAs layer is improving as well.
Compositional Modulations and Vertical Two-Dimensional Arsenic-Precipitate Arrays and in Low Temperature Grown Al0.3GA0.7AS
Authors: Hsieh K.Y. , Hwang Y.L. , Zhang T. , Kolbas R.M.
Published: March 2011

Compositional modulations and arsenic precipitates in annealed A10.3Ga0.7As layers which were grown at a low substrate temperature (200° C) by molecular beam epitaxy (MBE) were studied by transmission electron microscopy (TEM). These layers were used as surface layer which were applied on metal-insulator-semiconductor (MIS) diode. The planar and cross sectional TEM micrographs reveal that compositional modulations occurred when the thickness of LT AIGaAs was over 1500Å. The wavelength of the modulations varies between 100-200 Å and the direction of the modulation is along \011]. The arsenic precipitates were formed after annealed and the distribution of them followed the compositional modulation. Vertical two dimensional arsenic-precipitates arrays were arranged in the low aluminum constitute region. These novel microstructures result from the strain-induced spinodal decomposition and the arsenic precipitates redistribution process.
Properties of an Array of Dislocations in a Strained Epitaxial Layer
Authors: Zhang Tong-Yi
Published: March 2011

The energy of a general array of dislocations in an epitaxial layer is formulated and expressed in terms of per unit area of interface. Several limiting cases are used to verify the solution and the results are compared to other independent treatments. The critical thickness required for the generation of an isolated dislocation is found by solving for the layer thickness which corresponds to a zero value of the formation energy. The critical dislocation density at a given thickness is also determined. An additional work required for sequential generation of dislocations in an epitaxial layer arises from dislocation-dislocation interaction and has to be expressed in terms of per unit length of dislocation line. The work hardening effect is found to increase sharply with decreasing distance between the fresh and the pre-existing dislocations once the distance falls below approximately twenty times the layer thickness. The additional work achieves the level of the self energy of an isolated dislocation when the distance between the fresh and the nearest pre-existing dislocation is comparable to twice the layer thickness.
Defect Reduction by Thermal Cyclic Growth in GaAs Grown on Si by Movpe
Authors: KÜrner W. , Dieter R. , Zieger K. , Goroncy F. , DÖrnen A. , Scholz F.
Published: March 2011

The growth of GaAs epilayers on Si should combine the advantages of both materials. The lattice mismatch and the difference in thermal expansion coefficients, however, result in the yet unsolved problems of high dislocation density and thermal stress in the GaAs layer. Recently, considerable improvements have been achieved by a ‘thermal cyclic growth’ (TCG) process. In this study we focus on the reduction of high defect concentration and dislocation density. The improvement of the epilayer quality is verified by DLTS, PL and DCXD. Results of TEM and DLTS measurements lead to the identification of a dislocation related defect.
Deep Levels Induced by SiCI4 Reactive Ion Etching in GaAs
Authors: Johnson N.P. , Foad M. A. , Murad S. , Holland M. C. , Wilkinson C. D. W.
Published: March 2011

Deep Level Transient Spectroscopy (DLTS) is used to investigate the effect of SiC14 Reactive Ion Etching (RIE) on GaAs. At high power (150-80 W) with high DC self bias (380-240 V), five deep levels trapping electrons are observed at energies of 0.30, 0.42, 0.64, 0.86 and ∼0.8 eV below the conduction band edge. Depth profiling reveals an approximate exponential decay of the concentration of the deep levels. At low power the induced concentration falls, the small concentration of remaining deep levels is close to control (no etching) samples. The induced deep levels can account for reduced conductances in n+GaAs wires defined by RIE under similar experimental conditions.
Optical and Electronic Properties of GaAs/AlAs Random Superlattices
Authors: Wang E.G. , Xu J.H. , Su W.P. , Ting C.S.
Published: March 2011

The optical and electronic properties of three-dimensional (3D) random GaAs/AlAs superlattices (SLs) has been studied by using a tight-binding Hamiltonian with secondneighbor interactions. We calculate three completely disordered sequences with the probability of GaAs layers being 30%, 50%, and 70%. The higher the GaAs composition, the narrower the indirect gap. An energy-level crossing is found at the bottom of conduction band, which originates from the M-state splitting induced by layer disorder. The localized states over two - four monolayers play an important role in the absorption edge of random SL. The highest absorption intensity of the band-edge transitions in our random models is about eight times stronger than that of short period ordered GaAs/AlAs SL. Our results are in good agreement with some recent photoluminescence measurements.
Interaction Between Defects and Tunneling Effect in Heterostructures
Authors: Stievenard D. , Lannoo M.
Published: March 2011

Due to the reduced size of quantum devices, defects play a dominant role in their electrical behaviour. We theoretically show that defects can change the electrical behaviour of a single barrier or a quantum well. For the barrier and the well, we have performed a quantum calculation of a defect assisted tunneling effect based on the WKB theory to describe the wave functions and on the Oppenheimer approach for the determination of the tunneling probability. The main effects are : appearance of a negative differential resistance (NDR) in the currentvoltage characteristics (I-V) of the single barrier and an apparent lowering of the band offset of the quantum well. In the latter case, we have experimentally measured this effect on an AlInAs-GaInAs-AlInAs well, using admittance spectroscopy. The apparent lowering is associated with a native defect located in the barrier, a defect studied using the DLTS technique.
Single-Source Precursors to Vanadium Nitride Thin Films
Authors: Winter Charles H. , Viejo Valerie C. , Proscia James W.
Published: March 2011

Vanadium nitride films reflect infrared radiation and are candidates for solar control coatings for glass. Herein we report our efforts to prepare new precursors to vanadium nitride coatings. Treatment of vanadium tetrachloride with primary alkylamines in dichloromethane affords vanadium chloride amides of the empirical formula [VCI2(NHR)2(NH2R)2]. The characterization and properties of these compounds is presented. The complexes [VC12(NHR)2(NH2R)2] can be sublimed at ca. 100°C (0.1 mmHg) and serve as single-source precursors to vanadium carbonitride films. Films have been deposited in the temperature range of 400-600°C on glass and silicon substrates. The film properties and characterization will be overviewed.
Assessment of Carbon Contamination in Titanium Nitride Films Deposited from the Reaction of Titanium (IV) Ciiloride and Amines
Authors: Williams Keith B. , Stewart Ogie , Reck Gene P. , Proscia James W.
Published: March 2011

The reaction of titanium (IV) chloride and amines in an atmospheric pressure chemical vapor deposition (APCVD) has been previously shown to produce high quality titanium nitride films. These films were gold in appearance with high infrared reflectivity and resistivities as low as 80 microhm-cm. In the present study, the carbon content of the amines was systematically increased and the carbon levels in the films measured by XPS. For primary amines carbon contamination was not detected. Films deposited from secondary and tertiary amines had measurable carbon contamination. Correlation of carbon contamination with electrical resistivity and infrared reflectivity is discussed. Scanning electron micrographs and x-ray diffraction of the films are presented.