bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual Stress in Diamond and Amorphous Carbon Films
Authors: Ager Joel W.
Published: April 2011

Both diamond and amorphous carbon films can contain substantial residual stresses (up to 10 GPa and higher) due to a combination of thermal and intrinsic effects. Residual stresses in the films limit the maximum thickness to which films can be grown and can lead to weakening and/or failure of the film/substrate interface. In addition, a quantitative measurement of the residual stress in the film is required for an accurate determination of the film/substrate interface fracture toughness. Spectroscopic measurements of residual stresses in diamond and amorphous carbon films based on frequency shifts of Raman-active phonon modes are presented. The spatial resolution of the technique is 1 μm in the lateral direction. In transparent materials such as single crystal diamond, stress profiles with 10 μm resolution in the axial direction can be measured. Examples of such stress profiles are presented for natural and CVD-grown single crystals. Raman measurements of thermal stress in thin polycrystalline diamond films on metal substrates are presented. Initial, spatially resolved measurements of large, compressive intrinsic growth stresses in high-hardness amorphous carbon films grown by ion beam techniques are presented. The accuracy of the Raman residual stress measurement depends on the film structure and is ±60 MPa for single crystal diamond, ±120 MPa for polycrystalline diamond, and ±500 MPa for hard amorphous carbon.
Local Stress Assessment of CVD Diamond with Micro-Raman Spectroscopy Up To 1200K
Authors: Chen Li-Chyong , Chen Kuei-Hsien , Lai Yen-Liang , Wu Jin-Yu
Published: April 2011

Raman spectra in CVD diamond films were measured at room temeprature and at high temperatures up to 1200 K. With micron spatial resolution, variations of Raman line from different crystals in the same sample were observed. Both single-peak and multiple-peak analyses were used to assess the stress distribution within the CVD diamond film. In addition, the evolution of Raman line position, line width, and line intensity was monitored as a function of annealing temperature and isothermal holding time. Both (100) and (111) CVD diamond crystals were studied. The detailed evolution of the Raman line width was found to depend on the crystallographic orientation. The temperature dependence of the Raman spectra for CVD and natural diamonds are compared.
Fracture, Fatigue and Indentation Behavior of Pyrolytic Carbon for Biomedical Applications
Authors: Ritchie R. O. , Dauskardt R. H. , Gerberich W. W. , Strojny A. , Lilleodden E.
Published: April 2011

The fracture, fatigue and indentation properties of pyrolytic carbon, both as a monolithic material and as a coating on a graphite substrate, are described in light of its use for biomedical implant applications, specifically for the manufacture of mechanical heart valve prostheses. From the perspective of determining properties that are important for the prediction of safe structural lifetimes in such prostheses, it is found that by traditional engineering standards, pyrolytic carbon has low damage tolerance, i.e., fracture toughness values between 1 and 3 MPa√m and susceptibility to subcritical crack growth by both cyclic fatigue and stress-corrosion cracking (static fatigue). Subcritical crack-growth rates are evaluated in simulated physiological environments for both through-thickness “long” cracks, and for physically “small” surface cracks, the latter measurements being performed for cracks initiated at hardness indents. The unusual deformation characteristics of indentation in pyrolytic carbon are described based on instrumented microhardness indentation and scanning probe microscopy (AFM/STM) studies.
Threshold Crack Size in A Pyrolytic Carbon for no Growth Under Cyclic Stress
Authors: Ling M A , Sines George H. , Gilpin C. Barclay
Published: April 2011

In this work, the fracture toughness of monolithic pyrolytic carbon and sandwich composites of this carbon on a graphite substrate were measured by a disk-shaped compact specimen and by using a tensile specimen. On this material, a large number of specimens that had small cracks induced by a Vickers diamond indenter were tested under cyclic stress. The existence of a true threshold stress intensity factor range for non-propagation of the cracks was demonstrated. Statistical confidence on pre-cracked specimens was obtained through testing a large number of specimens to a very long lifetime of the order of 109 cycles.
Fracture Toughness and Subcritical Crack Growth in CVD Diamond
Authors: Kant A. , Drory M. D. , Ritchie R. O.
Published: April 2011

The fracture toughness, stress corrosion and cyclic fatigue properties of polycrystalline chemical vapor deposited (CVD) diamond have been investigated on thick (˜100 to 300 μm) free-standing films. Specifically, the fracture toughness, Kc, of diamond was determined using indentation methods and for the first time by the tensile testing of pre-notched fracture-mechanics type compact-tension samples. Measured Kc values were found to be between 5 and 7 MPa-m1/2 by either method and to be apparently independent of grain size and shape. Studies on subcritical crack growth (i.e., at stress intensities less than Kc) indicated that CVD diamond is essentially immune to stress-corrosion cracking under sustained loads in room air, water and acid environments. Corresponding experiments to examine susceptibility to cyclic fatigue are currently being performed using indentation-precracked cantilever beams cycled in three-point bending.
Diamond Films for Tribomechanical Systems
Authors: Boving H. J. , Hänni W. , Maillat M. , Dan J. P. , Niedermann P.
Published: April 2011

Progress made in the field of CVD diamond has enabled to strengthen and diversify mechanical applications of these coatings. Although CVD diamond is presently mainly in the laboratory stage, it is possible to recognize the main applications in the field of tribology as follows: cutting tools, metal working tools, bearings and mechanical components. In these 4 areas diamond films can be beneficial, but there are still several problems related to nucleation, adhesion and surface roughness of the coating, to be solved.
Friction and Wear of Amorphous Hydrogenated Carbon
Authors: Heidger S. L.
Published: April 2011

Uniform amorphous hydrogenated carbon (a-C:H) films with surface roughnesses ranging between 1 nm and 4 nm were produced by radio frequency self biased plasma enhanced chemical vapor deposition (rf PECVD) on > Silicon substrates using 100% methane precursor gas mixture, rf power densities ranging between 0.11 W/cm2 and 1.07 W/cm2, and pressures ranging between 0.67 Pa and 40 Pa. Reciprocating sliding friction experiments were conducted on the a-C:H films with hemispherical, silicon nitride pins in dry nitrogen and in 60% relative humidity. The coefficients of friction and the wear rates of the a-C:H were very low in dry nitrogen, ranging from 0.03 to 0.05, and from 1.1 × 108 mm3/Nm to 2.3 × 10−6 mm3/Nm, respectively. In 60% relative humidity, the initial coefficients of friction were approximately 0.30. However, the steady state coefficients of friction of the a-C:H films ranged from 0.10 and 0.30, depending on the deposition conditions. The wear rates ranged from 2.0 × 10−9 mm3/Nm to 8.9 x 10−8 mm3/Nm in 60% relative humidity. Raman microprobe spectroscopy and Auger electron spectroscopy (AES) revealed that sliding friction was transforming the a-C:H films into a material primarily composed of sp2 bonded carbon with increasing short range order. Qualitatively, the amount of wear which occurred corresponded to the extent that the structural changes progressed. The a-C:H films were further characterized by scanning electron microscopy (SEM) and surface profilometry.
The Erosive Behaviour of Diamond
Authors: Pickles C S James , Coad E J , Jilbert G H , Field J E
Published: April 2011

Diamond exists in many forms including natural diamond, synthetic diamond produced at high temperatures and pressures, polycrystalline diamond composites (PCD's) and most recently chemical vapour deposited (CVD) diamond. The liquid impact behaviour of these materials has been characterised in terms of a single and multiple impact damage threshold velocity which was obtained using a jet technique capable of reaching velocities of 600 m s−1. The multiple impact damage threshold velocity is a highly reproducible parameter which is invaluable in comparing the rain erosion resistances of different materials.

The sand erosion resistances of the various forms of diamond have also been evaluated using a specially designed sand blasting apparatus at velocities up to 270 m s-1. The extent of damage is quantified by mass and transmission loss as a function of impact velocity.

The results of these experiments reveal that the exceptional mechanical properties of diamond cause it to have an equally exceptional response to erosion.
Vibrational Signatures of Diamond Surfaces
Authors: Köhler Th. , Frauenheim Th. , Porezag D. , Pederson M.
Published: April 2011

Stable clean and hydrogenated diamond (100) and (111) surface reconstructions found by density-functional molecular-dynamics (DF-MD) are characterized by their vibrational properties. For sufficiently large surface slab supercells we have calculated the surface top-three-layer projected vibrational spectra and reproduced the main features obtained from experiments. The various reconstructions of the diamond surface yield rich spectra of surface modes involving excitations of dimers, trimers and chains. We classify most characteristic surface modes and discuss correlations to peaks observed in surface sensitive experiments. The vibrational spectra represent signatures of the considered surfaces that might be used to understand and to classify as grown diamond surfaces.
Synthesis, Properties and Applications of Superhard Amorphous Coatings
Authors: Tamor Michael A.
Published: April 2011

Low-friction/ultralow-wear coatings allow “surface engineering” for improved performance and durability, and enable use of new light weight or low cost materials. The accepted correlation of wear resistance with hardness suggests use of ceramic carbides and nitrides, with diamond being the ultimate anti-wear coating. While any of these may be deposited by chemical vapor deposition, the high cost (due to low deposition rates and high capital costs) and (usually) high deposition temperatures makes CVD coating impractical for cost-sensitive automotive applications. While rarely as hard as their crystalline counterparts, hard amorphous films exhibit similar (and occasionally superior) tribological properties and may be deposited on virtually any material at low cost. The highly nonequilibrium deposition process - conformal plasma reactive ion plating (CP-RIP) - allows tailoring of film properties and exploration of completely new compositions with no crystalline counterparts. Factors controlling the mechanical and optical properties of amorphous hard coatings, and recent progress in their application will be reviewed.
Stability, Chemical Bonding and Vibrational Properties of Amorphous Carbon at Different Mass Density
Authors: Köhler Th. , Frauenheim Th. , Jungnickel G.
Published: April 2011

We describe correlations between the atomic-scale structure and the global electronic and vibrational properties in amorphous carbon versus mass density. The model structures have been generated by applying different annealing regimes using a density-functional based molecular-dynamics (DF-MD) method. The stability of the amorphous modifications and the calculated vibrational density of states (VDOS) are strongly affected by the density and the annealing sequences, altering the chemical composition, the sp/sp2/sp3-clustering, the structure and related physical properties. A mass density of 3.0 g/cm3 is confirmed as a magic density favoring the formation of most stable a-C modifications having lowest defect densities and maximum band gap. In analyzing the vibrational spectra and the localization of modes in comparison with crystalline diamond and graphite, we identify the spectral signatures for chemically different bonded species and defects, that may be used for comparison with related Neutron-, Raman- and IR- work.
Relationship of Processing Conditions to Growth Rate and Quality of Diamond Grown by Chemical Vapor Deposition
Authors: Angus John C. , Cassidy William D. , Wang Long , Wang Yaxin , Evans Edward , Kovach Christopher S. , Tamor Michael A.
Published: April 2011

Diamond quality is strongly coupled to growth rate. Incorporation of nondiamond (sp2) carbon and morphological instabilities both increase with increasing growth rates. The intersection of twins with the growth surface produces re-entrant corners that enhance growth in the plane of the twin. Morphology and the development of texture both depend on substrate temperature and methane concentration and hence on growth rate. Experimental evidence and modeling results that relate growth rates and quality to controllable process parameters are reviewed.
High-Temperature Indentation of Natural Diamond and the Quest for Lonsdaleite
Authors: Pirouz P. , Garg A. , Ning X. J. , Yang J. W. , Xiao S. Q.
Published: April 2011

Attempts were made to produce bands of hexagonal diamond (Lonsdaleite) by high-temperature indentation of cubic diamond. (011) wafers of type I diamond were indented over the temperature range 1000–1300°C and the microstructure of the indentation plastic zone investigated by transmission electron microscopy (TEM). No hexagonal diamond was produced; instead, the plastic zone consisted of arrays of dislocations lying on the {001} planes. A possible mechanism for the generation of such dislocations, and reasons for the absence of hexagonal diamond, are discussed.
Indentation Characterisation of Carbon Materials
Authors: Field John S. , Swain M. V.
Published: April 2011

High precision force-displacement measurements of various forms of glassy and graphitic carbon have been made with a Berkovich and spherical tipped indenter. The force-displacement data show almost complete recovery despite contact pressures exceeding a considerable fraction of the elastic modulus. With a spherical tipped indenter the transition from elastic to inelastic response could be readily identified. It was found that the extent of the hysteretic response with a spherical indenter increased with increasing load. Only minor differences in the force-displacement response of crystalline graphite indented normal to the basal plane and the glassy carbon was identified. A simple model for interpreting the force-displacement data is developed. These results are compared with indentations made on diamond like carbon films on various substrates.
The Effects of Collimator Life Time on the Ti and Tin Film Growth Rates and Conformalities in Sputter Deposition Processes: Experiments and Simulations
Authors: Liao Hung , Stippel Hannes , Reddy Krishna , Geha Sam , Brown Kevin , Lindorfer Philipp , Saha Samar , Lin Zhou , Cale Timothy
Published: April 2011

Experimental and simulation studies were conducted in an attempt to understand the effects of collimator life time on the Ti and TiN film growth rates and conformalities in sputter deposition processes. The Ti and TiN films were deposited with and without collimation. The hexagonal cells of the collimator used in this study have a 1:1 aspect ratio. A Monte Carlo based simulator was used to calculate the angular distributions of species exiting from a collimator cell and the percentage decrease in the rate of film growth as a function of the collimator life time. Then, a low pressure deposition process simulator, EVOLVE, was used to predict the conformalities of deposited films in contacts or vias, assuming that the films were uniformly deposited on the side-walls of collimator cells. We conclude that the loss in growth rate is largely due to the shrinkage in the cross sectional area of the collimator cell inlets. We arrive at this conclusion after comparing an estimated film thickness on the collimator side-walls with experimental measurements. With extended collimator usage, the predicted and experimental film profiles in contacts or vias show increasing bottom coverage and decreasing side-wall coverages.
Low Temperature (≥ 400°C) Silicon Pyrometry AT 1.1μm with Emissivity Correction
Authors: Sturm J. C. , Reddy A.
Published: April 2011

In this work we have examined the experimental low-temperature limits of 1.1μm pyrometry for the measurement of the temperature of silicon wafers and aluminumcoated silicon wafers at temperatures under 700°C in RTP chambers. In-situ emissivity correction in the same range has also been demonstrated with a single detector for radiation and reflection measurements. Temperatures as low as 450°C have been measured on metallized surfaces with an accuracy of better than 10°C without any a priori knowledge of the wafer emissivity.
Rapid Thermal Processing-Manufacturing Perspective
Authors: Thakur R. P. S. , Schuegraf K. , Fazan P. , Rhodes H. , Zahorik R.
Published: April 2011

While repeatable and accurate measurement of temperature in rapid thermal processing (RTP) remains a subject of ongoing research, inception of large-diameter wafers and deep subhalf micron design rules may be viewed as good news for implementing RTP during the development phase for later transfer to volume manufacturing. To date, the only well-established application of RTP in manufacturing is silicide annealing. However, research during the past decade has demonstrated the feasibility of using RTP to replace essentially all furnace-based thermal processes in sub-half micron process flows. These developments in the RTP capability offer several technological and economic benefits such as improved defect control, higher product yields, and faster development cycles for DRAM-type technologies at a reduced cost and with an earlier entry of the driver products during the revenue-generating period.

In this paper, we review several applications of RTP such as silicide anneals, borophosphosilicate glass (BPSG) reflow, dopant activation, and rapid thermal nitridation (RTN) and discuss the integration issues related to advanced process flows. Furthermore, we highlight important manufacturing parameters like throughput, machine cost and uptime, software and hardware issues, wafer dimensional analysis, and simulation expectations. While considering volume manufacturing, we make some calibration and process control recommendations.
Characterization of Rapid Nitrided Ultrathin SiO2 Films By XPS and SCS
Authors: Yan H. , Wong S. P. , Chan R. W. M. , Kwok R. W. M. , Feng W. X.
Published: April 2011

Ultrathin SiO2 dielectric layers of thickness less than 100Å on silicon substrates have been prepared by dry oxidation and rapid thermal nitirdation (RTN). In this study, X-ray photoelectron spectroscopy and surface charge spectroscopy had been applied to study the nitrogen distribution in the dielectric layers and the change in the interface state density (Dit) due to the nitrogen incorporation. It is found that most of the incorporated nitrogen is located near the dielectric/Si interface and the nitrogen content increases with the RTN temperature. For the electrical properties, we found that the Dit, after RTN slightly decreases and the breakdown field strength deduced from the dielectric surface potential was enhanced by the incorporation of nitrogen.
Controlled Thin Oxidation and Nitridation in a Single Wafer Cluster Tool
Authors: Sagnes I. , Laviale D , Glowacki F. , Blanchard B. , Martin F.
Published: April 2011

abstract

For both advanced MOS technologies (gate length ≤ 0.25.μm) and EEPROMs, the quality and reproducibility of thin dielectric films (≤ 6 nm) are essential. To obtain such dielectrics involves very precise control of the silicon surface preparation and gate oxide growth. Furthermore, research into such supplementary properties of oxide as improved SiO2/Si interface resistance to current injections or enhanced p+gate resistance to boron penetration in the channel may require nitridation treatment. Such a sequence of steps can be carried out under controled atmosphere using a cluster tool. This paper presents the preliminary results obtained in a single wafer cluster tool on i) the surface preparation under ozone of a silicon wafer immediately after diluted liquid HF treatment and ii) the nitridation of the 6 nm gate oxide under low temperature, low pressure gaseous NO. It is shown that the NO molecule can be successfully used in Rapid Thermal Processing (RTP) and allows gate oxides to be nitrided with properties at least equivalent to those obtained under N2O nitridation, but with a strikingly reduced thermal budget.
Emissivity Of Rough Silicon Surfaces: Measurement And Calculations
Authors: Xu H. , Sturm J. C.
Published: April 2011

The directional reflectance and approximate emissivity of rough silicon wafers were measured by reflection measurements using a single point detector and a broad area illumination source. Experiments were also performed to determine the cone angle of the incident light required to properly measure the emissivity of rough backsides. Based on surface roughness parameters acquired with an Atomic Force Microscope, reflectance calculations were performed within the framework of the Beckmann-Spizzichino model. The results are qualitatively consistent with experimental observations.
RTA-Preparation of β-FeSi2 Layers from MBE-Grown Fe-Si Films Deposited on Si and Relaxed SiGe (100) Substrates
Authors: LíBezný M. , Poortmans J. , Dekoster J. , Degroote S. , Vantomme A. , De Lange B. G. M. , Langouche G. , Nijs J.
Published: April 2011

Rapid thermal annealing (RTA) of Fe-Si layers co-deposited on n- and p- type Si (100) and Si-capped relaxed Si0.6Ge0.4 (100) substrates was studied. Relaxed (100) Si0.6Ge0.4 epitaxial layers represent a pseudo-matched substrate for the β-FeSi2 phase. Fe-Si layers with a 1:2 composition ratio were deposited at room temperature in an MBE system. Samples were then subjected to a rapid thermal annealing in a H2/N2-atmosphere in the temperature range between 500 and 800 °C. Conversion electron Mössbauer spectroscopy showed that the layers consist of the β-FeSi2 phase. Nomarski microscopy revealed crystal grains of the diameter from 5 to 10 μm. Cross-section transmission electron microscopy study found smooth surfaces and interfaces. No significant structural defects were found inside the grains. Differences between current-voltage characteristics of simple devices prepared on these layers agree with the trends expected from their band diagrams.
Influence of Oxygen on Rapid Thermal Co-Diffusion of Phosphorus and Aluminium in Silicon
Authors: Mahfoud K. , Hartiti B. , Muller J. C. , Siffert P.
Published: April 2011

Local motion, diffusion and interaction of impurities in solids are important aspects of semiconductor material and device processing. Rapid thermal processing (RTP) is extremely concerned and appears to offer significant advantages in these areas. As oxygen is one of the dominant impurities present in silicon, various applications require different level of oxygen to improve the device performance.

In this work, we have taken the advantage of this feature to study the effects of the oxygen concentration in silicon on the rapid thermal co-diffusion of phosphorus and aluminium. In particular, we will show that the large enhancement of the minority carrier diffusion length (LD) due to this process can be related to the presence of oxygen and carbon which influences during the thermal cycle are of importance.
Modeling, Simulation and Control of Single Wafer Process in Cluster Tool Base on Ft-Ir In-Line Sensor
Authors: Liu Shaohua , Solomon Peter , Carpio R. , Fowler B. , Simmons D. , Wang J. , Wise R. , Imper G. , Riley N. B. , Moslehi M. , Ravindra N. M.
Published: April 2011

This paper outlines our current approach to utilize infrared reflectance spectroscopy for thin film measurement in the semiconductor industry. The multi-layer thickness and doping concentration of IC wafers can be determined by a single angle, unpolarized infrared reflectance measurement performed using Fourier transform infrared spectrometer. A computer algorithm, which matches theoretical tc measured infrared reflectance spectra, was successfully employed to determine multiple thin film properties.
Density-Functional Based MD Studies of Low-Energy Atom Collisions onto Diamond and Graphite
Authors: Uhlmann S. , Stephan U. , Frauenheim Th. , Seifert G.
Published: April 2011

The near-surface implantation of hyperthermal neutral atoms with (15 - 75) eV onto diamond (111) and graphite substrates is studied by molecular-dynamics (MD) using a density-functional (DF) based non-orthogonal tight-binding (TB) scheme. Depending on the initial energy and the impact point the atoms penetrate beneath the surface forming regions of local disorder and stress. The energy partition during the collision is analyzed yielding results about penetration and displacement threshold. After a final relaxation of the structures the penetration depths of the colliding particles are determined. The structural topology and the electronic properties of the induced defects and surface modifications are discussed. The penetration thresholds for noble gas atoms, hydrogen and carbon and the atomic-size dependent bulge arising after the subplantation process into a graphite substrate have been determined.
Evaluation of Anisotropic Film Structure of Amorphous Alloy by Computer Simulation
Authors: SATO A. , YAMAMOTO H.
Published: April 2011

A film growth of a virtual GdCo amorphous binary alloy was studied with a molecular dynamics simulation. A deviation of the atomic environment δ and an atomic pair distribution index η were calculated to evaluate the atomic structure of the prepared film. It was found that an anisotropic atomic distribution is induced in the film. The value of δ for a Gd atom environment is of the order of 10−4 and is almost in quantitatively agreement with the experimental value. The anelastic deformation is affected by the roughness of the substrate and becomes large in the film deposited on a smooth substrate. The value of η shows that the atomic pairs preferentially orient toward a horizontal film plane. The obtained results strongly support a single ion model as a main origin of a perpendicular magnetic anisotropy experimentally observed in amorphous rare earth-transition metal alloy films.
Parameters for Feature Evolution Models in Plasma Etching from Molecular Dynamics Simulation
Authors: Helmer B.A. , Graves D. B. , Barone M.E.
Published: April 2011

The impact of Si with incident energy Ei (0.1, 1, 5, 10, 20, and 50 eV) and angle θi (0° and 60° from the surface normal) into three model Si surfaces with varying degrees of F coverage (0 ML F, ∼ 1 ML F, and ∼2 ML F) was simulated using classical molecular dynamics (MD). From the simulation results, the probabilities for incident Si reflection and removal of surface Si and F were obtained as a function of Ei, θi, and F surface coverage. In general, these probabilities were observed to depend significantly on these parameters. This result implies that feature evolution simulations require surface reaction models with the necessary functionality in order to make quantitative predictions.
Characterization of Quantum Heterostructures. A Simulation Method Combining the Evaluation of Lattice and Electrons Configuration and TEM Imaging.
Authors: Mattei G. , Mazzone A. M.
Published: April 2011

This work analyzes the characterization of the structural properties of quantum heterostructures by HREM. A simulation of atomistic type is used to construct a Fe/Ag bilayer few nm thick and the HREM image of this structure is calculated by using a standard dynamical diffraction method. The comparison of the two calculations indicates that the interfacial disorder spans few layers and can be resolved against the background of two well-registered lattices.
The Potential Effect of Multilayer Patterns on Temperature Uniformity During Rapid Thermal Processing
Authors: Hebb Jeffrey P. , Jensen Klavs F. , Egan Erik W.
Published: April 2011

This work aims to systematically gain an understanding of the effects of multilayer patterns on wafer temperature uniformity during rapid thermal processing, and explore possible solutions to the problem. Steady state and transient wafer temperature distributions are simulated by combining a detailed reactor transport model with multilayer electromagnetic theory to predict wafer radiative properties. A generic axisymmetric RTP system with single-side illumination is used as a testbed to explore pattern effects for a simulated source/drain implant anneal.
Silicon AD-Dimer Binding on Si(100)
Authors: Bedrossian Peter J. , Smith Arthur P. , Jonsson Hannes
Published: April 2011

Isolated Si ad-dimers nucleate predominantly on Si(100) substrate dimer rows at room temperature. Using tunneling microscopy (STM), we find that, while ad-dimers oscillate between two mutually orthogonal orientations, the geometry with the ad-dimer bond perpendicular to the substrate's dimer bonds is the more stable. This observation confirms a prediction of ab initio calculations with a gradient correction for the energies of ad-dimers in various configurations, which differs from that of the local density approximation (LDA).
Simulation of Multicomponent Thin Film Deposition and Growth
Authors: Burmester C. P. , Wille L. T. , Gronsky R.
Published: April 2011

Results from a multicomponent Monte Carlo simulation of the deposition and growth of YBa2Cu3O7 are presented and discussed. In particular, a detailed examination of the growth modes active during different morphological growth conditions is performed. At higher deposition rates, both [001] and [100] epitaxial variants (‘c’ and ‘a’ type growth, respectively) are observed to grow by modes attributed to the classic Volmer-Weber mechanism. At very low deposition rates, the film is observed to grow in a distinct, cyclic, multi-stage process. Small islands of [001] epitaxy nucleate and grow to one unit cell height followed by primarily horizontal growth or “ledge extension” until one unit cell layer has formed. This process then repeats. Simulated RHEED amplitude data from this growth process compares favorably to experimentally obtained data.
Hot Carrier Degradation of Gain in Bipolar Transistors
Authors: Kizilyalli Isik C. , Bude Jeff D.
Published: April 2011

In this paper hot carrier related aging of n-p-n bipolar transistors is investigated experimentally and theoretically to bring physical insight into the bipolar transistor hFE (common emitter current gain) degradation. Electrical stress experiments are performed on transistors with different base doping profiles at varying temperatures. Detailed process simulations are performed to determine the doping profiles of the base-emitter junction. Monte Carlo transport simulations are then performed at different temperatures and bias conditions to determine the electron and hole distribution functions in the baseemitter junction. AT&T's 0.8 μ.m BICMOS technology is used to fabricate the experimental bipolar transistor structures. For this non-self aligned technology we attribute hFE degradation to the presence of hot holes and secondary electrons which are generated by hot hole impact ionization. This feed-back due to impact ionization has a dominant effect on the high energy tails of the distribution of both holes and electrons even when the overall current multiplication is low. Simple hot electron energy transport models do not contain the complexity to properly describe ionization feedback and carrier heating, and are therefore inadequate. An exponential dependence of the transistor lifetime on BVEBO is deduced for constant voltage stress (Vstress < BVEBO) conditions, confirming the importance of secondaries in the process of degradation.
Coupled Stress Evolution in Polygranular Clusters and Bamboo Segments in Near-Bamboo Interconnects
Authors: Knowlton B. D. , Clement J. J. , Frank R. I. , Thompson C. V.
Published: April 2011

Electromigration-induced failure of near-bamboo interconnects depends strongly on the number and lengths of both polygranular clusters and bamboo segments in a line. We have used numerical techniques to calculate the stress profile as a function of position and time for near-bamboo lines with a variety of microstructures. Our results show that coupling of stress profiles between nearby clusters can affect the time to reach a pre-defined critical, or failure, stress. The degree of coupling depends both on the spacing between clusters and the ratio of the diffusivities between polygranular and single crystal regions. Electromigration failure is therefore sensitive to the distribution and lengths of bamboo segments, and the likelihood of long polygranular clusters coinciding with adjacent short bamboo segments.
Real-Time Tem Studies of Electromigration in Submicron Aluminum Runners
Authors: Riege S. P. , Hunt A. W. , Prybyla J. A.
Published: April 2011

Direct real-time observations of electromigration (EM) in submicron Al interconnects were made using a special sample-stage which allowed TEM observations to be recorded while simultaneously heating and passing current through the sample. The samples consisted of 4000 Å thick Al(0.5wt%Cu) patterned over a TEM-transparent window into five runners in parallel, with linewidths 0.2, 0.3, 0.5, 0.8, and 1.0 μm. Both passivated and unpassivated samples were examined. A current density of 2 x 106A/cm2 was used with temperatures ranging from 200 - 350°C. The experiments were done using constant voltage testing, and we used a special sample design which dramatically minimized Joule-heating. Our approach has allowed us to directly observe voids form, grow, migrate, pin, fail a runner, and heal, all with respect to the detailed local microstructure of the runners.
Mechanism of Electromigration Failure in Al Thin Film Interconnects Containing Sc
Authors: Kim Choong-Un , Kang S. H. , Génin F.Y. , Morris J. W.
Published: April 2011

In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc were tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM.
Circuit Reliability Simulation
Authors: Hu Chenming
Published: April 2011

In designing a complex circuit, designers make a large number of circuit simulations, design changes and optimizations and can predict the circuit's performance reasonably accurately before committing it to silicon. It would be unthinkable to bypass detailed circuit simulation and optimization and rely on simple design rules and the testing of finished IC's to discover errors or to find out if the performance of the circuit meet specifications. Yet, this is basically the way IC reliability is treated today. A logical alternative is to predict circuit reliability at the circuit design stage through reliability simulation.

Reliability simulator BERT is used to illustrate the physical models and approaches used to simulate the hot electron effect, oxide time-dependent breakdown, electromigration, bipolar transistor gain degradation, and radiation effects. The goal is to make circuit reliability simulation a part of the IC design process.
Influence of Film Thickness and Capping Layer on the Mechanical Properties of Copper Films
Authors: Keller R.-M. , Kuschke W.-M. , Kretschmann A. , Bader S. , Vinci R.P. , Arzt E.
Published: April 2011

Substrate curvature and X-ray technique were used to study the mechanical properties of Cu films. Stress-temperature curves were measured using both methods. An additional analysis of the X-ray peak width allows us to estimate grain size and dislocation density as a function of temperature. It can be shown that a capping layer changes the mechanical properties of a Cu film strongly and that in capped films dislocation processes seem to be more important than diffusion at high temperatures.
The Effect of Cu Distribution on Post-Patterning Grain Growth and Reliability of Al-1%Cu Interconnects
Authors: Knowlton B. D. , Frank R. I. , Thompson C. V.
Published: April 2011

The reliability of Al-Cu interconnects is a strong function of both grain structure and the Cu content and distribution. Because pre-patteming and post-patterning grain growth are affected by the presence of Al2Cu precipitates, the effects of grain structure and Cu distribution are interrelated. We have studied the effect of Al2Cu precipitate spacing on interconnect reliability independent of grain size effects. This was accomplished by varying the thermal history of the continuous films to produce samples with identical grain structures, but different precipitate spacings. The precipitate spacing in continuous films was varied by an order of magnitude, from 2.6 μm to 25. pm. Lines were then patterned from each sample and tested. Lifetime testing results show that the reliability of lines with smaller precipitate spacings can be roughly an order of magnitude higher than that of lines with a larger precipitate spacing. We have also qualitatively studied the effects of Cu distribution on post-patterning grain growth. We found that precipitates retard post-patterning grain evolution, leading to reduced reliability. These results suggest strategies for developing thermal histories which will lead to optimal reliability.
Failure in Tungsten-Filled Via Structures
Authors: Clement J. J. , Lloyd J. R. , Thompson C. V.
Published: April 2011

Failure of the tungsten-filled via interconnect structure is modelled. Two mechanisms contributing to void growth are considered: relief of stress due to differential thermal expansion, and electromigration. A self-limiting void volume is predicted, resulting in a self-limiting resistance increase which is a function of structure geometry and the void morphology. The relative contributions of the two mechanisms change significantly as the temperature and current density are reduced from accelerated test conditions, affecting the extrapolation of test results to service conditions. Modified procedures for extrapolating lifetimes are discussed, as well as suggested process changes to improve reliability.
The Effect of Post W-Etchback Cleaning Treatments and Implementation of Refractory Metal Buffer Layers on the Electromigration Performance of TiN/AlCu/TiN/Ti Metallization Systems
Authors: Roede Henk , Gounelle Catherine , Giroux François , Doedel Wim
Published: April 2011

TiN/Ti films employed as glue layers for a blanket/etchback W plug technology show a significant surface contamination after the W-etchback process. An Al film deposited directly on a contaminated TiN/Ti underlayer exhibits a very weak texture, increasing the susceptibility to electromigration. Reliability tests confirm that the electromigration performance of a TiN/AlCu/TiN/Ti metallization system with a W plug technology, is significantly inferior to interconnecs that do not employ this plug technology. To improve the electromigration performance of this metallization system, several TiN surface cleaning treatments were evaluated. Also, the impact of the implementation of refractory metal buffer layers, before Al deposition was investigated. Analysis was performed by means of several surface analysis techniques, Al texture measurements and wafer-level reliability tests. It has been demonstrated that the contamination needs to be removed completely, or to be covered by a refractory buffer layer in order to restore the Al texture and to recover the proper electromigration resistance.
Effect of Via Etch Profile and Barrier Metal on Electromigration Performance of W-Filled Via Structure in TiN/AlCu/TiN Metallization
Authors: Ting Larry M. , Dixit G. , Jain M. , Littau K. A. , Tran H. , Chang M. , Sdsfha A.
Published: April 2011

In this study, we have evaluated electromigration performance of W-plug vias, fabricated with process variations in via hole etching as well as in via barrier deposition, on a TiN(barrier)/AlCu/TiN metallization system. We found that via etch profile scheme as well as deposition conformity for via barrier can significantly affect W-plug via lifetimes. The results indicate that the quality of contact with AlCu layer of bottom level metal is a critical factor in determining via lifetime. Precise control of via etching or by use of conformal via barrier to ensure a good barrier between W-plug and the AlCu of bottom level metal is essential for achieving reliable via structures.
Reliability Issues with Mixed-Signal CMOS Technology
Authors: Lahri Rajeeva , Chen Hung-Sheng , Zhao Ji , Gadepally Kamesh , Teng C.S.
Published: April 2011

In a Mixed-Signal IC, both digital and analog circuits exist on the same chip. Analog circuit blocks require technology attributes like precise device matching, low parametric drifts and low noise. These requirements raise additional reliability issues, over and above the reliability concerns associated with digital circuits. CMOS device reliability for mixed-signal technologies can be enhanced by modifying device architecture and improving gate oxide integrity. Interconnect metallurgy plays an important role in determining electromigration related contact/via resistance change which may impact matching of devices and resistor pairs. Appropriate source/drain engineering, device design and utilizing nitrided gate oxide has been shown to produce extremely stable devices. This article will cover process architecture and material issues related with device stability and interconnect metallurgy issues related with contact/via stability, especially with W-Plugs.
Microscopic Measurements of Electromigration Damage Using Electrical Measurements
Authors: K Jones Brian
Published: April 2011

Continuous measurements have been made of the changes in several electrical quantities of Al 4%Cu tracks during the lifetime under electromigration stress. The changes in resistance, second harmonic and the second harmonic delay have been used to determine the changes in the track cross-section, resistivity and temperature. During most of the lifetime the results are consistent with a linear increase in the microscopic damage occurring uniformly throughout the track. During the final phase of the life there is evidence of large void formation with subsequent healing. Considerable information can be obtained about these processes and the extent to which they are reversible. The observed events are compared with the changes which have been predicted by specific mechanisms.
Electromigration Induced Drift and Noise in a Single Aluminum Via
Authors: ALERS G. B. , OATES A. S. , BEVERLY N.L.
Published: April 2011

We have examined small changes in the resistance of a single aluminum via test structure with a resolution of 10-8 ohms. The via is roughly one cubic micron and contains a well defined TiN diffusion barrier. The high resolution of these resistance measurements allows the observation of atomic drift rates corresponding to roughly 100 atoms/second into and out of the well defined via structure. Resistance changes are observed with moderate current densities in the temperature range of 100°C to 200°C. We observe reversible increases and decreases in the resistance caused by the accumulation of atoms at the diffusion barrier within the via. Comparisons can be made to recent models for the transient electromigration induced vacancy drift. We are able to extract microscopic electromigration parameters as well as differentiate between copper and aluminum as the initial diffusing element.
The Influence of Thermal-Mechanical Effectson Resistance Changes During and After Electromigration Experiments
Authors: SCORZONI A. , DE MUNARI I. , STULENS H. , D'HAEGER V.
Published: April 2011

This paper is focused on the non-linear resistance behaviours often detected by means of high resolution resistometric methods both at the very beginning of an electromigration (EM) test, and after the high stressing current inducing EM is switched off. It is shown that temperature steps, always present at the beginning or after EM, are the triggering events for different, often reversible, physical phenomena contributing to resistance changes. Precipitation-dissolution of alloyed elements is perhaps the most important one, while other mechanisms, like the combined effect of hydrostatic stress relaxation and void volume change, should cancel out. These effects, however, don't exclude a possible simultaneous effect on the resistance of accumulation/relaxation of EM damage. Experimental results are collected by means of different, complementary techniques.
Hillock Formation in Tensile Loaded Films
Authors: Harris Karen E. , King Alexander H.
Published: April 2011

While hillocks usually form to relieve compressive stresses in thin films resulting from electromigration or a difference in thermal expansion in the film and substrate, we have observed hillock formation in tensile-loaded films. We have used transmission electron microscopy to study hillocks which formed in free-standing gold thin films of 25nm nominal thickness. Grain growth during 150°C anneals reduced the grain boundary area and associated free volume, placing the films under tensile stress. While hillock formation could only increase this stress, large single crystal or polycrystalline hillocks with thicknesses up to three times the film thickness are observed after 400°C annealing, after long room temperature anneals, and during TEM observation. These observations suggest the operation of a hillock formation mechanism not explained by any existing hillock formation theories.
Yield Stress in Single Crystal and Polycrystalline Al Films
Authors: Traub A. , Volkert C. A.
Published: April 2011

The stresses in single crystal and polycrystalline Al films were determined by wafer curvature measurements during temperature cycling. Both elastic and plastic behavior was observed. The single crystal film exhibited anisotropic yield stresses indicating that dislocation glide is the dominant deformation mechanism. The polycrystalline film exhibited similar behavior, although without the anisotropy, indicating that it too deforms by dislocation glide. Unlike the single crystal film, the yield stress in the polycrystalline film varied depending on thermal and deformation history. These effects are attributed to the presence of grains and grain boundaries in the polycrystalline film.
Solution Synthesis and Characterization of Lithium Manganese Oxide Cathode Materials
Authors: Voigt J. A. , Boyle T. J. , Doughty D. H. , Hernandez B. A. , Johnson B. J. , Levy S.C. , Tafoya C. J. , Rosay M.
Published: April 2011

A nonaqueous coprecipitation process has been developed to prepare controlled stoichiometry lithium manganese oxalate precipitates. The process involved mixing a methanolic Li-Mn nitrate solution with a methanolic solution containing tetramethylammonium oxalate as the precipitating agent. The resulting oxalates were readily converted to a variety of phase pure lithium manganese oxides at moderate temperatures (≤600°C), where the phase formed was determined by the initial Li/Mn ratio in the starting solution. Metal cation dopants have been incorporated into the oxalate precipitate by dissolving the appropriate metal nitrate in the Li-Mn precursor solution The various starting solutions, oxalate precipitates, and calcined oxides have been extensively characterized using a variety of techniques, including 7Li NMR, TGA/DTA, SEM, and XRD. Results indicate that a strong interaction occurs between Li and Mn in the nitrate solution which carries over into the oxalate phase during precipitation. The morphology and the crystallite size of the oxide powders were shown to be controlled by the morphology of the oxalate precursor and the oxalate calcination temperature, respectively. The results of initial cathode performance tests with respect to dopant type (Al, Ni, Co) and concentration for LiMn2O4 are also reported.