bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diode-laser-based Atomic Absorption Monitors for Physical Vapor Deposition Process Control
Authors: Wang Weizhi , Hammond R. H. , Fejer M. M. , Beasley M. R. 
Published: April 2011

ABSTRACTAtomic absorption spectroscopy with tunable diode lasers has been performed for monitoring and study of the physical vapor deposition process. The combination of the wavelength-modulation spectroscopy with diode lasers and the balanced detection scheme guarantees the high sensitivity and reliability of the system. Direct measurements of atomic flux in e-beam evaporated yttrium and barium, which are components in YBCO superconducting thin films, have been demonstrated. The measured velocities show that the e-beam evaporated atoms are in a non-thermal-equilibrium state, dependent on source conditions, implying that the flux measurement rather than a simple density measurement for rate control is necessary. Comparison with quartz crystal monitors shows that the present scheme, employing two laser beams counterpropagating at an angle to the substrate surface for measuring directly the velocity component normal to the substrate surface, can provide a pressure-independent flux measurement. In yttrium, which has an additional significantly populated metastable level, results show that pressure-independent flux measurement requires measurements at both the ground state and the metastable levels. Efforts have also been made to extend the accessible wavelengths of diode lasers to the UV region by using nonlinear optical frequency doubling techniques for other technologically important elements.
Growth of La2−x SrxCuO4 and La2CuO4+δ thin films by Reactive Coevaporation
Authors: Sato H. , Yamamoto H. , Naito M. 
Published: April 2011

ABSTRACTThin films of La2−xSrxCuO4 (LSCO) and La2CuO4+δ (LCO) were grown by reactive coevaporation. We obtained LSCO thin films on (001) LaSrA104 (LSAO) substrates with Tc(R=0) = 44 K, which is higher than that for bulk samples. A structural analysis indicates that the increase in Tc is due to compressive strain generated by the lattice mismatch. A similar strain effect is suggested from the substrate dependence of Tc for superconducting LCO thin films, for which Tc(R=0) reached 50 K on (001) LSAO substrates. We also succeeded in obtaining high-quality LSCO ultrathin films without any buffer or cap layers on (001) LSAO substrates, but not on substrates of other materials with the larger lattice mismatch with LSCO. These results demonstrate that the lattice mismatch with the substrates is important in thin-film growth of LSCO and LCO.
Rheed Studies of a-Axis Oriented DyBa2Cu3O7 Films Grown by All-MBE
Authors: Bozovic Ivan , Eckstein J. N. , Bozovic Natasha , O'Donnell J. 
Published: April 2011

ABSTRACTReal-time, in-situ surface monitoring by reflection high-energy electron diffraction (RHEED) has been the key enabling component of atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) of complex oxides. RHEED patterns contain information on crystallographic arrangements and long range order on the surface; this can be made quantitative with help of numerical simulations. The dynamics of RHEED patterns and intensities reveal a variety of phenomena such as nucleation and dissolution of secondary-phase precipitates, switching between growth modes (layer-by-layer, step-flow), surface phase transitions (surface reconstruction, roughening, and even phase transitions induced by the electron beam itself), etc. Some of these phenomena are illustrated here, using as a case study our recent growth of atomically smooth a-axis oriented DyBa2Cu3O7 films.
In-Situ Diagnostics at High Pressures: Ellipsometric and Rheed Studies of the Growth of Yba2Cu3O7
Authors: Blank Dave H. A. , Rogalla Horst 
Published: April 2011

ABSTRACTPulsed Laser and Sputter Deposition are used for the fabrication of complex oxide thin films at relatively high oxygen pressures (up to 0.5 mBar). This high pressure hampers the application of a number of in-situ diagnostic tools. One of the exceptions is ellipsometry. Using this technique we studied in-situ the growth of off-axis sputtered Yba2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Furthermore, the oxidation process from O(6) to O(7) has been studied by performing spectroscopic ellipsometry during isobaric cooling procedures.Another suitable in-situ monitoring technique for the growth of thin films is Reflection High Energy Electron Diffraction (RHEED). In general this is a (high) vacuum technique. Here, we present an RHEED-system in which we can observe clear diffraction patterns up to a deposition pressure of 0.5 mBar. The system has been used for in-situ monitoring of the heteroepitaxial growth of YBa2Cu3 06+x on SrTiO3 by pulsed laser deposition.
In Situ Initial Growth Studies of (Sr, Ca)CuO2 ON SrTiO3 by High Pressure Rheed
Authors: Koster Gertjan , Runders Guus J. H. M. , Blank Dave H. A. , Rogalla Horst 
Published: April 2011

ABSTRACTThe initial growth of pulsed laser deposited SrCuO2 (SCO) and CaCuO2 (CCO) on SrTiO3 has been studied using high pressure Reflection High Energy Electron Diffraction (RHEED) and Atomic Force Microscopy (AFM). For this, we developed a Pulsed Laser Deposition (PLD)- RHEED system, with the possibility to study the growth and to monitor the growth rates, in situ, at typical PLD pressures (10–50 Pa). In case of depositing oxide materials, high oxygen pressures are desired. Moreover, crystallinity can be improved using higher oxygen pressures and therefore higher temperatures. With this technique we are able to obtain atomically flat films, a first step towards multi-layer structures.In this paper we present the initial growth studies of SCO and first results incorporating CCO layers in a SCO matrix.
Real-time Monitoring of semiconductor growth by Spectroscopic ellipsometry
Authors: Johs B. , Hale J. , Herzinger C. , Doctor D. , Elliott K. , Olson G. , Chow D. , Roth J. , Ferguson I. , Pelczynski M. , Kuo C. H. , Johnson S. 
Published: April 2011

ABSTRACTin situ Spectroscopic Ellipsometry (SE) is an optical technique which is well suited for the monitoring of epitaxial semiconductor growth, due to its high surface sensitivity and non-invasive nature. In this work, SE systems were installed on both MBE and MOCVD deposition systems to monitor the epitaxial growth of InxGa1−xAs and InxAl1−xAs compounds on InP substrates. The structures grown include thick lattice matched In0.53Ga0.47As buffer layers (for HBT collectors), and strained RTD structures. SE was used to monitor in real-time layer composition and thickness during growth. To enhance the precision and accuracy of the SE determined growth parameters, it was necessary to optimize the SE data analysis strategies. A methodology to determine the best spectral region for the SE data analysis in the presence of noise and systematic effects (such as angle of incidence uncertainty, detector wavelength shifts, surface roughness, uncertainty in surface temperature, non-ideal growth modes, etc.) is presented. Using the optimized data analysis strategies, long term SE-determined InxGa1−�As composition accuracy (as verified by ex situ x-ray measurements) of ±0.002 in ‘x’ was achieved. SE thickness measurements of ultra-thin (<30Å) strained AlAs barrier layers were also in excellent agreement (±0.5Å) with real-time photo-emission oscillation measurements.
Material Balance Modeling of End-Point Uniformity in Silicon Dioxide Plasma Etching
Authors: Chamberst J. J. , Min K. , Hauser J. R. , Parsonst G. N. 
Published: April 2011

ABSTRACTAs wafer diameters increase, monitor wafers become more costly for process characterization and real-time sensors become more attractive. Process-state sensors are generally easier to implement than direct wafer-state sensors, but process-state sensors are usually not thought to provide wafer-state analysis. Utilizing a process-state sensor, such as a mass spectrometer, for wafer-state information will result in new approaches for sensing, optimizing, and controlling integrated circuit fabrication processes. We used a two stage differentially pumped mass spectrometer system sampling directly from an electron cyclotron resonance (ECR) chamber to sense the process-state and monitor end-point during silicon dioxide etch. The end-point uniformity is characterized using mass spectroscopy and material balance modeling. Specifically, using CF4 and D2 etch gases, the partial pressure of CO-containing etch products decays near the endpoint, and the average initial slope is directly correlated with the uniformity determined from optical interferometry thickness measurements. Changing the ECR magnet geometry defines the etch uniformity, and the resulting CO+ end-point signal is sensed with the mass spectrometer. By analyzing the initial slope of the CO+ signal near the end-point, a correlation exists between uniformity and the mass spectrometry signal. A COF2 etch product material balance provides a concentration versus time end-point model which substantiates the correlation between the mass spectrometer signal and the etch uniformity. This model is valid for any sensor that detects a change in the COF2 concentration at the end-point.
Simulations of Electromigration At A Tungsten/Aluminum Junction
Authors: Enver A. , Povirk G. L. 
Published: April 2011

ABSTRACTFinite element solutions to problems of electromigration and stress-driven diffusion are presented. The numerical procedures are based on a formulation that assumes bulk diffusion, so that diffusion along grain boundaries and interfaces is not explicitly taken into account. Two cases are considered: (1) a tungsten via/aluminum line junction, and; (2) a one-dimensional case with a blocking boundary at one end of the line. The results show that line geometry can significantly affect the magnitude of the stresses that develop, although in each case the maximum hydrostatic stress in the line was proportional to the square root of time.
Under Bump Metallization Development For High Sn Solders
Authors: Korhonen T. M. , Hong S. J. , Su P. , Zhou C. , Korhonen M. A. , Li C.-Y. 
Published: April 2011

ABSTRACTSeveral under bump metallisation (UBM) schemes using Ni or CuNi alloys as the solderable layer were investigated. Cr or Ti was used as the adhesion layer. The UBM pads of different compositions were sputter deposited on silicon wafers and patterned using standard photolithographic processes. Eutectic Sn-Pb solder balls were reflowed on top of the pads. The resulting interfacial microstructures were examined by SEMIEDX analysis of cross-sectioned samples. The integrity of the UBMIsolder interface was characterized by micromechanical shear testing of flip chip test samples. Growth of intermetallic layers was found to be significantly slower in Ni and CuNi schemes compared to pure Cu. The joints on Ni and CuNi had also a better adhesion at the UBM/solder interface, and in the shear tests the fracture occurred through the solder
Observation of Dislocation DisAppearance in Aluminum Thin Films and Consequences for Thin Film Properties
Authors: Müllner P. , Arzt E. 
Published: April 2011

ABSTRACTDislocation structures in Al-Cu thin films have been studied by transmission electron microscopy (TEM). We have observed that the contrast of interface dislocations disappears in the electron beam. We assume that the contrast dissolution is due to the spreading of the dislocation core at the crystalline/amorphous interface or due to a diffusive movement of the dislocation through the oxide. In any case, the relaxation is assumed to be controled by irradiation induced diffusion. As a consequence, the short range stresses and at least partly also the long range stresses of the dislocations relax. This relaxation changes the interaction force between dislocations and may thus significantly affect the mechanical properties of thin films. It is concluded that interaction between interface dislocations may not be responsible for the high temperature strength of aluminum films.
Theoretical Analysis of Electromigration-Induced Failure of Metallic Thin Films
Authors: Maroudas Dimitrios , Gungor M. Rauf , Ho Henry S. , Enmark Matthew N. 
Published: April 2011

ABSTRACTA comprehensive theoretical analysis is presented of the failure of metallic thin films due to electromigration-induced morphological evolution of transgranular voids. Fully self-consistent dynamical simulations emphasize the important effects on void dynamics of the surface diffusivity anisotropy, together with the strength of the applied electric field and the void size. The simulation results are discussed in the context of an approximate linear stability theory. Our simulations predict formation of wedge-shaped voids, as well as failure due to propagation of slit-like features emanating from void surfaces, in excellent agreement with recent experimental observations.
Tensile Strength and Fracture Toughness of Surface Micromachined Polycrystalline Silicon Thin Films Prepared Under Various Conditions
Authors: Tsuchiya Toshiyuki , Sakata Jiro , Taga Yasunori 
Published: April 2011

ABSTRACTA new tensile tester for thin films was developed to evaluate the reliability of the microelectro- mechanical devices. This tester uses the grip that fixes a thin film specimen to a probe by electrostatic force. We applied this tester for polycrystalline silicon (poly-Si) thin films prepared under various conditions. The microstructure of the film is controlled by the crystallizing temperature. The process conditions and the microstructures that contribute to the strength of poly-Si film are identified by the tensile strength and the fracture toughness. The mean tensile strength of each specimen size ranges from 1.8 to 3.7 GPa, and the fracture toughness calculated from the strength of the notched specimen ranges from 1.9 to 4.5 MN/m3/2. The 1000°C annealed film has higher strength and toughness than the other films because of the high annealing temperature and the small grain size. The contributions to the strength are evaluated by the additional annealing at 1000°C for the low temperature annealed films.
The Relationship Between Near-Surface Mechanical Properties, Loading Rate And Surface Chemistry
Authors: Mann A. B. , Searson P. C. , Pethica J. B. , Weihs T. P. 
Published: April 2011

ABSTRACTThe presence of thin surface films and adsorbate layers on both metals and ceramics can cause dramatic changes in the mechanical response of the material. A similar, related, variation in tribological properties has also been observed. Though the importance of surface effects is well known and widely documented, the exact physical and chemical mechanisms that are operating remain poorly understood. The development of point probe techniques now permits the examination of mechanical and tribological properties on the same length scale as the surface films. Recently, the utilization of these testing techniques has provided a clear insight into the mechanical processes which are operating on the atomic scale. The nanoindentation results presented here show that the mechanical deformation of an individual nano-contact is a highly dynamic phenomena in which the tip-momentum on contact, as well as the loading rate during the indentation, dictate the observed mechanical properties of the material. These results indicate that the initiation of plastic deformation is dependent on the stability of atomic-size surface asperities which can be deformed irreversibly by the high stresses generated during the initial contact. Additionally, the generation of dislocations and the presence of discontinuities in the loading curve are shown to depend upon the loading rate. More significantly, it has been found that modifying the surface chemistry can cause dramatic changes in both the mode of deformation and the time-dependence of nano-scale mechanical properties. The principal conclusion that can be drawn is that the high stresses which operate over short distances make time and temperature dependent phenomena, such as diffusion and the dissipation of energy via phonons, of vital importance in determining the near-surface mechanical properties of a material. Such effects are further magnified in tribological processes where normal and tangential loading of the surface leads to the repeated making and breaking of nano-asperity contacts.
Thermal Cycling Fatigue In Aluminum-Alloy Thin Films On Silicon Substrate
Authors: Koike J. , Utsunomiya S. , Maruyama K. 
Published: April 2011

ABSTRACTThermal cycling was performed in Al-lmo%Si thin films deposited on Si wafers. After a given number of cycling between room temperature and 723 K, residual stress was measured at room temperure. Residual stress was found to increase with increasing the cycling number up to the 4th cycle, followed by further a continuous decrease by further cycling. The intial increase was found to be related to the increase of lattice dislcocations and their tangling. The following decrease was caused by crack formation along grain boundaties or by film delamination in some cases.
Mechanical Characterization Of Ultra-Thin, Hard-Disk Overcoats Using Scratch Testing And Depth-Sensing Indentation
Authors: Hay J. L. , White R. L. , Lucas B. N. , Oliver W. C. 
Published: April 2011

ABSTRACTTwo series of five diamond-like carbon (DLC) coatings were sputtered under nominally identical conditions, but to different film thicknesses of 20 nm and 105 nm. First, the hardness of each sample was determined by depth-sensing indentation. Hardness measurements were substrate-affected to some extent for all samples but especially so for the 20 nm coatings. Two types of scratch tests were performed in an attempt to isolate and characterize the top coatings. The first was a wear test, which consisted of moving the sample back and forth repeatedly under a small constant load. The residual damage was inconsistent, but appeared to be a function of the composite, or substrate-affected hardness. The second test was a single-pass scratch in which the normal load was ramped linearly. For all samples, the friction coefficient was approximately constant as a function of load. Furthermore, samples with the same top coats yielded similar friction coefficients, regardless of the coating thicknesses. Friction coefficient decreased with hydrogen content and to some extent, increased with hardness, as measured on the 105 nm samples. The friction coefficient measured during a ramp-load scratch offers an alternative for characterizing ultra-thin films, when indentation alone yields measurements that are significantly affected by the substrate.
A Method for Independent Measurement of Elastic Modulus and Poisson's Ratio of Diamond-Like Carbon Films
Authors: Cho Sung-Jin , Lee Kwang-Ryeol , Eun Kwang Yong , HAN Jun Hee , Ko Dae-Hong 
Published: April 2011

ABSTRACTA simple method to measure the elastic modulus and Poisson's ratio of diamond-like carbon (DLC) films deposited on Si wafer was suggested. This method involved etching a side of Si substrate using the DLC film as an etching mask. The edge of DLC overhang free from constraint of Si substrate exhibited periodic sinusoidal shape. By measuring the amplitude and the wavelength of the sinusoidal edge, we can determine the strain of the film required to adhere to the substrate. Combined with independent stress measurement by laser reflection method, this method allows calculation of the biaxial elastic modulus, E/(1 − v), where E is the elastic modulus and v Poisson's ratio of the DLC films. By comparing the biaxial elastic modulus with plane-strain modulus, E/(1 −v2), measured by nano-indentation, we could further determine the elastic modulus and Poisson's ratio, independently. This method was employed to measure the mechanical properties of DLC films deposited by C6H6 r.f. glow discharge at the deposition pressure 1.33 Pa. The elastic modulus, E, increased from 94 to 128 GPa as the negative bias voltage increased from 400 to 550 V. Poisson's ratio was estimated to be about 0.22 in this bias voltage range. For the negative bias voltages less than 400 V, however, the present method resulted in negative Poisson's ratio. The limitation of the present method was discussed.
Microstructure And Wear Resistance Of Doped Diamondlike Carbon Prepared By Pulsed Laser Deposition
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Oktyabrsky S. , Sankar J. , Narayan J. 
Published: April 2011

ABSTRACTWe have investigated the microstructure and tribological properties (wear resistance) of diamondlike carbon (DLC), DLC doped with Cu and DLC doped with Ti deposited by a sequential pulsed laser ablation of two targets onto Si(100) substrates. The composition of these films was determined by Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy(XPS). Raman spectroscopy and detailed analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dominated by sp3 bonded carbon. Wear resistance measurements made on these samples by means of the “crater grinding method” showed that DLC + 2.75%Ti has the highest wear resistance, while that of undoped DLC has the lowest among the samples. The improvement of wear behavior of the doped films was attributed to the reduction of internal compressive stress due to the presence of more compliant atoms, as indicated by the G-peak position shift to smaller Raman shift. The XPS studies showed the evidence for the formation of Ti- C bonding in the Ti doped films. Thus we expect metal-doped DLC coatings can have better tribological properties than the undoped, highly stressed DLC coatings.
Development of Mechanical Stress in Cuni(mn) Films During Temperature Ramping: Related Mechanisms
Authors: Brückner W. , Baunack St. , Pitschke W. , Thomas J. 
Published: April 2011

ABSTRACTThis paper focusses on the development of biaxial stress in Cu0.57Nio.42Mno.ol thin films during annealing in Ar and, for comparison, in vacuum. Besides stress-temperature measurements also resistance-temperature investigations as well as chemical and microstructural characterization by Auger electron spectroscopy, scanning and transmission electron microscopy, and X-ray diffraction were carried out. To explain the stress evolution, atomic rearrangement (excessvacancy annihilation, grain-boundary relaxation, and shrinkage of grain-boundary voids) and oxidation were considered. Up to 250 - 300 °C grain-boundary relaxation was found to be the dominating process. A sharp transition from compressive to tensile stress between 300 °C and 380 °C is explained by the formation of a NiO surface layer
Stress Characterization of Sputtered PZT Films
Authors: Mescher M. J. , Reed M. L. , Schlesinger T. E. 
Published: April 2011

ABSTRACTIn this work we show that stress in sputter deposited lead zirconate titanate (PZT) films can be controlled by variation of both deposition and annealing temperatures. These films were deposited via reactive rf magnetron sputtering using a Pb1.25Zr. 52Ti. 48 03 composite target and 02 as a reactive gas in an Ar ambient. Variation of stress as a function of deposition and annealing temperature was characterized. The deposited film composition was determined from x-ray fluorescence measurements. There is a strong correlation between film stress, composition, and crystallographic orientation. Stress was determined from the deflection of released SiO 2/Pt cantilever beams. We show that films with a wide range of intrinsic stress can be deposited which still exhibit good piezoelectric properties, making the fabrication of reliable thin film piezoelectric actuators possible.