Multilayer Thin Film Materials Research Articles

An Edge Detection Algorithm for SEM Images of Multilayer Thin Films

In processing multilayer thin film materials, scanning electron microscopy (SEM) is commonly employed for observation. In images of SEM, backscattered electron (BSE) images is particularly suitable for distinguishing different components and layers of the films. However, at high magnification levels, BSE images often have blurriness and noise, leading to low edge sharpness. This study proposes a method for improving the integrity and accuracy of the edges. First, we segment the image into different contrast regions using the masking algorithm. Second, we enhance the images in separate regions by the enhancement algorithm. Finally, we combine the regions by logical operations. In instantiation, we implement our approach on SEM-BSE images. It was found that the edges are significantly sharpened through the assessment of the edge evaluation algorithm.

Thermal Spike Responses and Structure Evolutions in Lithium Niobate on Insulator (LNOI) under Swift Ion Irradiation

Irradiating solid materials with energetic ions are extensively used to explore the evolution of structural damage and specific properties in structural and functional materials under natural and artificial radiation environments. Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry and has been widely applied in various fields of photonics, electronics, optoelectronics, etc. Based on 30 MeV 35Cl and 40Ar ion irradiation, thermal spike responses and microstructure evolution of LNOI under the action of extreme electronic energy loss are discussed in detail. Combining experimental transmission electron microscopy characterizations with numerical calculations of the inelastic thermal spike model, discontinuous and continuous tracks with a lattice disorder structure in the crystalline LiNbO3 layer and recrystallization in the amorphous SiO2 layer are confirmed, and the ionization process via energetic ion irradiation is demonstrated to inherently connect energy exchange and temperature evolution processes in the electron and lattice subsystems of LNOI. According to Rutherford backscattering/channeling spectrometry and the direct impact model, the calculated track damage cross–section is further verified, coinciding with the experimental observations, and the LiNbO3 layer with a thickness of several hundred nanometers presents track damage behavior similar to that of bulk LiNbO3. Systematic research into the damage responses of LNOI is conducive to better understanding and predicting radiation effects in multilayer thin film materials under extreme radiation environments, as well as to designing novel multifunctional devices.

Analysis of multi-layer thin-film materials using benchtop XRD and XRF systems

Analysis of multi-layer thin-film materials using benchtop XRD and XRF systems

Rigorous prediction of Raman intensity from multi-layer films.

In the Raman probing of multilayer thin film materials, the intensity of the measured Raman scattered light will be impacted by the thickness of the thin film layers. The Raman signal intensity will vary non-monotonically with thickness due to interference from the multiple reflections of both the incident laser light and the Raman scattered light of thin film interfaces. Here, a method for calculating the Raman signal intensity from a multilayer thin film system based on the transfer matrix method with a rigorous treatment of the Raman signal generation (discontinuity) is presented. This calculation methodology is valid for any thin film stack with an arbitrary number of layers with arbitrary thicknesses. This approach is applied to several thin film material systems, including silicon-on-sapphire thin films, graphene on Si with a SiO2 capping layer, and multilayer MoS2 with the presence of a gap between layers and substrate. Different applications where this method can be used in the Raman probing of thin film material properties are discussed.

Bifurcation in deformation mechanism to overcome strength-ductility paradox in metal-ceramic multilayer thin-films

Nanocrystalline multilayer thin-films are manufactured in configurations of alternating porous ceramic (TiN) layers of relatively high thickness (hceramic) with metal (Ti) layers of low thicknesses (0.8 nm < hmetal < 34 nm) and keeping a constant modulation ratio (η ∼ hceramic/hmetal ∼ 17.5). As hmetal decreases, the overall co-deformation mechanism in the multilayer films bifurcates into the dislocation dominant confined layer slip (CLS) mechanism in the metal and diffusional creep dominant processes in the porous ceramic layer at hmetal ∼ 6.7 nm. This bifurcation leads to simultaneously achieving the highest strain hardening rate due to the CLS mechanism in one layer and the highest strain rate sensitivity value due to the diffusional flow in the other and overcoming the strength-ductility paradox in multilayer thin-film materials at low temperatures.

Heat Conduction in Multilayered Thermoelectric Materials with Multiple Cracks

Multilayer thin-film thermoelectric materials are of technological importance. This paper describes a method to analyze the heat conduction in a multilayered thermoelectric plate containing some non-collinear cracks. The material properties in one layer may be different from those in another even though each layer may still be homogeneous. Using the Fourier integral transforms, the boundary value problem is reduced to a system of general singular integral equations. The model is sufficiently general to account for any number of layers and any number of cracks. As a numerical illustration, the electric flux intensity factor, energy flux intensity factor and thermal flux intensity factor for a three-layer plate specimen with two cracks are presented. The effects of strip width on the electric flux intensity factor and thermal flux intensity factor are studied.

Recent Developments in the X-ray Reflectivity Analysis

X-ray reflectivity (XRR) is a powerfull tool for investigations on surface and interface structures of multilayered thin film materials. In the conventional XRR analysis, the X-ray reflectivity has been calculated based on the Parratt formalism, accounting for the effect of roughness by the theory of Nevot-Croce conventionally. However, the calculated results have shown often strange behaviour where interference effects would increase at a rough surface. The strange result had its origin in a serious mistake that the diffuse scattering at the rough interface was not taken into account in the equation. Then we developed new improved formalism to correct this mistake. However, the estimated surface and interface roughnesses from the x-ray reflectivity measurements did not correspond to the TEM image observation results. For deriving more accurate formalism of XRR, we tried to compare the measurements of the surface roughness of the same sample by atomic force microscopy (AFM), high-resolution Rutherford backscattering spectroscopy (HRBS) and XRR. The results of analysis showed that the effective roughness measured by XRR might depend on the angle of incidence. Then we introduced the effective roughness with depending on the incidence angle of X-ray. The new improved XRR formalism derived more accurate surface and interface roughness with depending on the size of coherent X-rays probing area, and derived the roughness correlation function and the lateral correlation length. In this review, an improved XRR formalism, considering the diffuse scattering and the effective roughness, is presented. The formalism derives an accurate analysis of the x-ray reflectivity from a multilayer surface of thin film materials.

Indentation-derived elastic modulus of multilayer thin films: Effect of unloading-induced plasticity

Abstract

Recent Developments in the X-Ray Reflectivity Analysis for Rough Surfaces and Interfaces of Multilayered Thin Film Materials

X-ray reflectometry is a powerful tool for investigations on rough surface and interface structures of multilayered thin film materials. The X-ray reflectivity has been calculated based on the Parratt formalism, accounting for the effect of roughness by the theory of Nevot-Croce conventionally. However, in previous studies, the calculations of the X-ray reflectivity often show a strange effect where interference effects would increase at a rough surface. And estimated surface and interface roughnesses from the X-ray reflectivity measurements did not correspond to the TEM image observation results. The strange result had its origin in a used equation due to a serious mistake in which the Fresnel transmission coefficient in the reflectivity equation is increased at a rough interface because of a lack of consideration of diffuse scattering. In this review, a new accurate formalism that corrects this mistake is presented. The new accurate formalism derives an accurate analysis of the X-ray reflectivity from a multilayer surface of thin film materials, taking into account the effect of roughness-induced diffuse scattering. The calculated reflectivity by this accurate reflectivity equation should enable the structure of buried interfaces to be analyzed more accurately.

High-Frequency Resistivity Measurement Method for Multilayer Soft Magnetic Films

We present a noncontact method to measure the resistivity of multilayer magnetic thin films under high-frequency excitation. A multilayer thin-film magnetic material separated by dielectric has been used in microfabricated magnetic components in power applications. High-frequency resistivity is necessary for predicting core loss in magnetic materials. Traditional measurement methods using contacting probes cannot provide a reliable measurement of the resistivity of multilayer thin-film materials. Noncontact methods eliminate the use of electrical probes. Eddy-current loss induced by an applied external magnetic field is measured and the high-frequency resistivity of multilayer material is extracted from eddy-current loss measurements. The application of this method to measure the resistivity of multilayer thin-film materials and magnetic materials is investigated. The high-frequency resistivity of a 6-μm-thick multilayer Co-Zr-O thin-film magnetic granular material is measured. Comparisons between theoretical and experimental results are presented.

Finite element modeling of stress variation in multilayer thin-film specimens for in situ transmission electron microscopy experiments

Multilayer thin-film materials with various thicknesses, compositions, and deposition methods for each layer typically exhibit residual stresses. In situ transmission electron microscopy (TEM) is a powerful technique that has been used to determine correlations between residual stresses and the microstructure. However, to produce electron transparent specimens for TEM, one or more layers of the film are sacrificed, thus altering the state of stresses. By conducting a stress analysis of multilayer thin-film TEM specimens, using a finite element method, we show that the film stresses can be considerably altered after TEM sample preparation. The stress state depends on the geometry and the interactions among multiple layers.

Nanoscale BixTe3/Sb2Te3 multilayer thin film materials for reduced thermal conductivity

Multilayer thin films were grown sequentially by evaporating solid antimony (III) telluride and bismuth (III) telluride as thermoelectric (TE) materials. The grown multilayer films have a periodic structure consisting of eleven or thirty-nine alternating thin film layers where each layer is 10nm thick. Rutherford backscattering spectrometry (RBS) analysis indicates that the deposited antimony telluride films have the desired stoichiometry of Sb2Te3 and the bismuth telluride films are Bi1.1Te3.0. A 3ω method thermal conductivity measurement system was used to measure the thermal conductivity of the multilayer thin films. 5MeV Si ion implantation was performed to improve the thermal conductivity of the multilayer thin films. Thermoelectric devices were fabricated with the multilayer thin films for the measurement of the cross-plane thermoelectric voltage and determination of Seebeck coefficient. The nanostructured multilayer thin film materials were found to have lower thermal conductivity than their conventional bulk materials, and Si ion implantation can decrease the thermal conductivity of the multilayer thin films.

Characterization of thin films on the nanometer scale by Auger electron spectroscopy and X-ray photoelectron spectroscopy

We describe two NIST databases that can be used to characterize thin films from Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) measurements. First, the NIST Electron Effective-Attenuation-Length Database provides values of effective attenuation lengths (EALs) for user-specified materials and measurement conditions. The EALs differ from the corresponding inelastic mean free paths on account of elastic-scattering of the signal electrons. The database supplies “practical” EALs that can be used to determine overlayer-film thicknesses. Practical EALs are plotted as a function of film thickness, and an average value is shown for a user-selected thickness. The average practical EAL can be utilized as the “lambda parameter” to obtain film thicknesses from simple equations in which the effects of elastic-scattering are neglected. A single average practical EAL can generally be employed for a useful range of film thicknesses and for electron emission angles of up to about 60°. For larger emission angles, the practical EAL should be found for the particular conditions. Second, we describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to be released in 2004. This database provides data for many parameters needed in quantitative AES and XPS (e.g., excitation cross-sections, electron-scattering cross-sections, lineshapes, fluorescence yields, and backscattering factors). Relevant data for a user-specified experiment are automatically retrieved by a small expert system. In addition, Auger electron and photoelectron spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra, and thus, provide more detailed characterizations of multilayer thin-film materials. SESSA can also provide practical EALs, and we compare values provided by the NIST EAL database and SESSA for hafnium dioxide. Differences of up to 10% were found for film thicknesses less than 20 Å due to the use of different physical models in each database.

Polymeric thin films of controlled complex refractive index formed by the electrostatic self-assembled monolayer process

This letter reports a method, the electrostatic self-assembled monolayer process, for the synthesis of multilayer thin-film materials with controlled complex refractive index. By incorporating appropriate precursor molecules in each monolayer and organizing the physical order of the multiple monolayers through the material, it is possible to achieve designed complex refractive index properties. In this work, the real part of the refractive index of materials formed by this process was controlled from 1.424 to 1.615, and the imaginary part was controlled from 0.00001 to 0.035, both at a wavelength of 550 nm. To our knowledge, this is the first time that experimental measurements of self-assembled thin films are presented to demonstrate that this method is useful for the design and synthesis of thin films of controllable refractive index.

Characterization of electrostatically self-assembled nanocomposite thin films

Multilayer thin films of metallic nanoclusters, polymers and other molecules have been formed using a novel electrostatic self-assembly method and analysed by multiple characterization techniques. Nanocluster size measurements, ellipsometry and UV-visible absorption spectroscopy have been used to confirm the linear build-up of the thin film thickness with the number of deposited nanocluster, polymer and other molecular layers. Auger electron spectroscopy allowed verification of the distribution of molecular species through thick films with multilayer segments containing different elements. Field emission scanning electron microscopy and atomic force microscopy permitted visualization of the morphologies of the outermost layers of the deposited films. Together, such characterization allows improved understanding and the basis for the design of multilayer thin film materials engineered to have specific molecular level structures and macroscopic functionalities.

Low Energy Ion Assisted Vapor Deposition

AbstractThe performance of multilayered thin film materials often depends sensitively upon the (physical) roughness and degree of (chemical) mixing at interfaces. Irradiation of a growth surface with an assisting ion beam is often used to modify surface roughness. Molecular dynamics has been used to explore the use of low energy (less than 20 eV) Xe+ and Ar+ assisted deposition of model Ni/Cu/Ni multilayers to control both physical roughness and chemical mixing. The study indicated that under normal ion incidence condition, ion energies as low as 3 eV could effectively flatten the relatively weakly bonded copper surface (and therefore the nickel on copper interface). Higher ion energies (at least 10 eV) were required to flatten the more strongly bonded nickel surface. Chemical intermixing by an exchange mechanism between a surface atom and an underlying atom in an already deposited layer depended upon the binding energy of the already deposited layer. As a result, significant chemical mixing occurred as 9 eV (and above) ions impacted with nickel atoms on an already deposited copper surface. At a given ion incident energy, (the heavier) Xe+ ions resulted in less roughness but more mixing. A modulated ion assistance strategy in which no assisting ion beam was used while depositing the first few monolayers of each new metal layer was found to successfully reduce both interfacial roughness and interlayer mixing.

Electron cyclotron resonance plasma etching of materials for magneto-resistive random access memory applications

Dry etching of multilayer magnetic thin film materials is necessary for the development of sensitive magnetic field sensors and memory devices. The use of high ion density electron cyclotron resonance (ECR) plasma etching for NiFe, NiFeCo, TaN, and CrSi in SF6/Ar, CH4/H2/Ar, and Cl2/Ar plasmas was investigated as a function of microwave source power, rf chuck power, and process pressure. All of the plasma chemistries are found to provide some enhancement in etch rates relative to pure Ar ion milling, while Cl2/Ar provided the fastest etch rate for all four materials. Typical etch rates of 3000A/min were found at high microwave source power. Etch rates of these metals were found to increase with rf chuck power and microwave source power, but to decrease with increasing pressure in SF6/Ar, CH4/H2/Ar, and Cl2/Ar. A significant issue with Cl2/Ar is that it produces significant metal-chlorine surface residues that lead to post-etch corrosion problems in NiFe and NiFeCo. However, the concentration of these residues may be significantly reduced by in-situ H2 or O2 plasma cleaning prior to removal of the samples from the etch reactor.

Giant magnetostrictive thin film materials and applications

Sputter-deposited magnetostrictive films present a new and interesting approach to realizing cantilever- and membrane-type actuators or resonant sensors in microsystems as they offer features like contactless, high frequency operation, simple actuator designs and a cost-effective manufacturing technique. An essential development was the preparation of low field positive and negative giant magnetostrictive amorphous, or multilayered thin film materials with magnetostriction exceeding 300 ppm at 0.02 T. Using these optimized films, Si-based microsystems (micropump, linear ultrasonic motor) have been realized which demonstrate the potential of magnetostrictive thin film actuators.

Auger electron spectroscopy and secondary ion mass spectrometry depth profiling with sample rotation

Recently, there has been a rapid increase in the application of multilayered structured materials, as opposed to bulk materials, in many areas of technological development. Accurate characterization of the structure and composition of advanced multilayers such as superlattices, quantum wells, contacts, and coatings is important for materials and device fabrication technology. Surface analysis techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy, and secondary ion mass spectrometry (SIMS) in conjunction with ion beam sputtering (sputter depth profiling) are at present the most widely used methods for characterization of modern multilayer thin film materials and devices. Ion-beam-induced surface topography, however, can limit depth resolution, and with SIMS, can also cause changes in the secondary ion yield. These changes are due to the high sensitivity of secondary ion yield to the local angle of incidence on sputter-roughened surfaces. Degradation of depth resolution and changes in secondary ion yields during sputter depth profiling have often limited studies of thin film interdiffusion, segregation, oxidation at interfaces, and impurity effects. Much theoretical and experimental work has been carried out to try to improve depth resolution including the use of low ion beam energy, high angle of incidence, and two ion guns. Recent studies of AES and SIMS with sample rotation have shown that depth resolution can be improved substantially and that constant secondary ion yields in SIMS can be achieved. We will first provide an overview of the studies made by various groups to improve depth resolution of metal multilayers using AES with rotation. Next we will review recent investigations of SIMS using sample rotation including studies of the effects of sample rotation on O 2 + ion-beam-induced topography, secondary ion yield, and the depth resolution of electronic, metallurgical and dielectric materials. The results presented demonstrate that SIMS with sample rotation provides constant secondary ion yield, and depth-independent depth resolution because sample rotation prevents ion-beam-induced roughness and reduces the effect of the inhomogeneity of low energy ion beams.

Magnetic thin films for data storage

Applications of magnetic thin films in data storage technology and areas for future research on thin films are discussed. Recent work at various laboratories indicates that magnetic recording densities of at least two orders of magnitude greater than those of today will be achieved. Among the advances in thin film technology which are needed to make this possible are the following: improved wear resistant overcoats for magnetic media; higher coercivity thin film media with isolated grain structure and multilayers to achieve low noise; high magnetization, high permeability multilayer thin film materials for advanced recording heads; giant magnetoresistive materials for advanced read heads. Although magnetic recording is expected to continue to dominate the data storage industry for the next two decades, magnetic-optic recording is likely to play an increasingly large role as a removable storage medium for large files of data involving images and multimedia. For increased storage density in magneto-optic recording, new magneto-optic thin film materials which are sensitive in the blue (or shorter) wavelength spectrum are needed. These films must not only provide large magneto-optic coefficients, but must also have the proper microstructure so that noise is low during readback. In order for these advances to be possible, new materials, new processing techniques, improved models and improved resolution imaging systems for studying both the magnetic and physical microstructure of thin films are needed.