Thickness Nonuniformity Research Articles

特定折射率材料及光学薄膜制备

A material with specific refractive index is prepared according to the requirement for the preparation of the laser protective coating for solar arrays. In this method,we apply the electron beam co-evaporation technique based on doped material preparation methods. Tests show that the refractive index of the doped material is 1. 75,according with the result of optimized scheme. The material is then used in the preparation of optical thin films to achieve a further optimization of the laser protective coating properties. Obtained laser protective coating has excellent properties and its solar radiation transmittance is increased by more than 6%. The film thickness mask technology is applied to improve the film thickness uniformity of large area thin films prepared by co-evaporation method. The thickness nonuniformity of doped material film prepared by this method within Φ400 mm area is less than 2.1%. It is showed that the technical process of electron beam co-evaporation technique is simple,reliable and suitable for practical applications. Test results of the film performance are consistent with the theoretical optimized results.

Influence by Casing Geometric Imperfection on Anti-Collapse Strength with Finite Element Calculation

This essay was to build a finite element model to find the influence by oil casing geometric imperfection on anti-collapse strength. Two types of oil casing, Ф177.8×10.36mm/P110 andФ127×9.19mm/ P110, was taken for the calculation, considering the influence on anti-collapse strength by casing with two elements separately, ovality and non-uniformity of wall thickness. The calculation show that the anti-collapse strength of perfect casing perform better than that of imperfect casing. Ovality is an important factor for the anti-collapse strength, and the anti-collapse strength decrease rapidly as the ovality increase. Non-uniformity of wall thickness is the less important factor for anti-collapse strength, and the anti-collapse strength decrease slightly and slowly while the non-uniformity of wall thickness increase.

Enabling graphene-based technologies: Toward wafer-scale production of epitaxial graphene

Abstract

Dynamic crushing behavior of random and functionally graded metal hollow sphere foams

Dynamic crushing responses of metal hollow sphere (MHS) foams with uniform, graded and random cell wall thicknesses were investigated. FE models are constructed for such foam structures based on hollow sphere model with different degrees of cell wall thickness non-uniformity. The plateau stress, the densification strain energy and the deformation modes are determined by using the FE models. The numerical results illustrate that the inertia effect has obvious influence at the impact side, but insensitive at the stationary side. Both the dynamic plateau stress and the densification strain energy at the impact side increase with increasing of crushing velocity, relative density and matrix material strength. The deformation modes of all models appear with three types which are the whole deformation, transitional deformation and the “I” shaped deformation. By comparing with the tradition model, result shows that density graded foam with the biggest density as the first impacted layer and least density as the last layer has some benefits in terms of maximum energy absorption with a minimum force level transmitted to the protected structures.

Enhancement of the ultraviolet absorption and Raman efficiencies of a few nanometer thick Si-on-insulator

We show that a 3–7 nm thick Si-on-insulator (SOI) film displays UV absorption and Raman enhancement compared to bulk Si at a proper thickness of the buried oxide layer between the film and Si substrate. Experiment shows ∼fivefold SOI Raman enhancement for 3–4 nm thick films while theory predicts enhancement up to a factor of ∼20 for 2 nm thick SOI. This discrepancy is attributed to non-uniformity of SOI thickness.

Reliability study of ultra-thin dielectric films with variable thickness levels

The time-dependent dielectric breakdown of ultra-thin gate oxides is one of the major reliability issues facing scaled metal-oxide semiconductor technologies. As the thickness of the gate dielectric film approaches its scaling limit, process issues such as poor wafer uniformity and oxide growth control become critical for ultra-thin gate dielectric reliability. This article investigates both the physics and statistical aspects of the reliability of the ultra-thin gate dielectric when film thickness variations are present. A physics-based Spatio-Temporal Monte Carlo Simulation (STMCS) model is developed to study the effects of thickness and thickness non-uniformity on dielectric reliability. Its use allows the root cause for the non-linear characteristic of the Weibull time-to-breakdown distribution observed in experimental studies to be revealed. In addition, a Bayesian Weibull Mixture (BWM) model is proposed to analyze the time-to-breakdown data considering the existence of thickness non-uniformity. Numerical results are presented that show that the proposed BWM model is significantly superior to the basic Weibull model for use in reliability projection. Both the STMCS and BWM models can successfully reproduce the experimentally observed non-linear characteristic of the Weibull time-to-breakdown distribution and thus can be used to predict device reliability when the dielectric films in a gate are of unequal thicknesses.

Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum

Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.

Strain analysis of the GaN epitaxial layers grown on nitridated Si(111) substrate by metal organic chemical vapor deposition

The strain analysis of GaN film on nitridated Si(111) substrate with different growth times between 0 and 660s via metal organic chemical vapor deposition (MOCVD) was conducted based on the precise measurement of the lattice parameters by using high-resolution X-ray diffraction (HR-XRD). The nitridation time (NT) was changed at a fixed growth condition. The a- and c-lattice parameters were measured, followed by the in-plane and out-of-plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values obtained, and were then discussed in the present study as functions of the NT. The biaxial strain and stress are also strongly affected by the non-uniformity of the SiNx buffer layer thickness.

Experimental and numerical analysis of micro/nanolayer coextrusion

Coextrusion is a common method used for producing multilayer films and sheets. Coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. This technique allows the processor to combine the desirable properties of multiple polymers into one structure with enhanced performance characteristics. The coextrusion process can be used to produce multilayer sheet, blown film, cast film, blow molding parts, tubing, wire coating and profiles. It is important to understand the effects of material and equipment parameters on the final micro-/nanolayer structures. Layers normally should have uniform thicknesses throughout the structure for optimal performance. However, layer thickness non-uniformities have been observed in many coextruded structures. It is a very complex and challenging problem due to coupled material and processing variables. This paper will discuss experimental programs as well as numerical modeling of the coextrusion process. The topics that will be covered include rheological measurements of coextruded structures as well as flow of coextruded structures through layer multipliers and dies.

Negative-[formula omitted] regime in the ac magnetic response of superconductor nanoshells

The time-dependent Ginzburg–Landau formalism is applied to analyze the vortex states and vortex dynamics in superconducting spherical nanoshells, subjected to mutually perpendicular strong dc and weak ac magnetic fields. We demonstrate that nonuniformity of the shell thickness can dramatically affect the ac magnetic response of a 3D array of superconducting nanoshells. Remarkably, this response is strongly influenced not only by the relevant geometric and material parameters and the ac-field frequency but also by the magnitude of the applied dc field: by changing this field the real part of the effective ac magnetic permeability can be tuned from positive values significantly larger than one down to negative values.

Oscillations in spectral behavior of total losses (1 − R − T) in thin dielectric films

We explain reasons of oscillations frequently observed in total losses spectra (1 - R - T) calculated on the basis of measurement spectral photometric data of thin film samples. The first reason of oscillations is related to difference in angles of incidence at which spectral transmittance and reflectance are measured. The second reason is an absorption in a thin film. The third reason is a slight thickness non-uniformity of the film. We observe a good agreement between theoretical models and corresponding measurements, which proves above statements on the origins of oscillations in total losses.

Electric field localizations in thin dielectric films with thickness non-uniformities

Thickness non-uniformities in electrostatic capacitors and in electroactive polymers – arising from manufacturing processes or electromechanical induced inhomogeneous deformations – may lead to drastic charge and electric field localizations and, ultimately, to an anticipated device failure. Based on a geometric interpretation of the Gauss equation enlightening the effect of the electrode curvature, we obtain an analytic expression of the electric field and of the surface charge density localization for non perfectly planar capacitors with symmetric thickness non-uniformities. The efficiency of the model is exploited by analyzing specific boundary value problems of technological interest.

Metal gate etch-back planarization technology

Planarization used in a gate-last CMOS device was successfully developed by particular technologies of SOG two-step plasma etch-back plus one special etch-back step for SOG/SiO2 interface trimming. The within-the-wafer ILD thickness non-uniformity can reach 4.19% with a wafer edge exclusion of 5 mm. SEM results indicated that there was little “disheffect" on the 0.4 μm gate-stack structure and finally achieved a good planarization profile on the whole substrate. The technology provided a CMP-less process basis for sub-100 nm high-k/metal gate-last CMOS integration.

Morphological Instability in Early Stages of Solidification of Pure Metals Part II: Experimental Analysis

A simple experimental setup has been used to investigate the morphological instability observed in many solidification processes. It is shown that the mold with smooth surface exhibits prominent thickness nonuniformities. Periodic grooves in the mold surface results in more uniform contact along the mold-shell interface, and therefore leads more uniform growth of the shell. Experimental results for the moving solidification front have also been compared to the results of a simple theoretical model introduced in Part I, and a good agreement has been obtained.

Dependence of wavefront errors on nonuniformity of thin films

In contrast to uncoated substrate, a nonlinear relationship of phase shift with the thicknesses of the thin film makes the calculation of wavefront aberration complicated. A program is compiled to calculate the wavefront aberration of multilayer thin film produced by thickness nonuniformity. The physical thickness and the optical phase change on reflection are considered. As an example, the wavefront aberration of the all-dielectric mirror is presented in ArF excimer lithography system with a typical thickness distribution. In addition, the wavefront errors of the thin film at wavelengths of 193 and 633 nm are compared in the one-piece and two-piece arrangements. Results show that the phase shift upon reflection of the thin film produced by thickness nonuniformity is very sensitive to the incident angle, wavelength, and polarization.

Morphological Instability in Early Stages of Solidification of Pure Metals Part II: Experimental Analysis

A simple experimental setup has been used to investigate the morphological instability observed in many solidification processes. It is shown that the mold with smooth surface exhibits prominent thickness nonuniformities. Periodic grooves in the mold surface results in more uniform contact along the mold-shell interface, and therefore leads more uniform growth of the shell. Experimental results for the moving solidification front have also been compared to the results of a simple theoretical model introduced in Part I, and a good agreement has been obtained.

Tuneable IR Photodetectors for Spectroscopic Applications

The concept and realisation of infrared micro-spectrometers using MEMS based Fabry-Pérot micro-filters integrated with IR photo-detectors are presented. By using five layer mirror structures, and stress optimisation in mirrors and actuators the tuning range from 1700 nm to 2300 nm has been achieved with maximum actuation voltage of only 18 V RMS. The average FWHM of the transmission peak was measured to be 35 nm, predominantly limited by thickness nonuniformity of individual mirror layers.

Variable-angle spectroscopic ellipsometry of considerably non-uniform thin films

A theoretical approach for including considerable thickness non-uniformity of thin filmsinto the formulae employed within variable-angle spectroscopic ellipsometry is presented. Itis based on a combination of the efficient formulae derived for the thickness distributiondensity corresponding to a wedge-shaped non-uniformity with dependences of the meanthickness and root mean square (rms) of thickness differences on the angle of incidence thattake into account the real non-uniformity of the shape. These dependences are derivedusing momentum expansion of the thickness distribution density. The derived formulaeare tested by means of numerical analysis. An application of this approach isillustrated using the optical characterization of a selected sample of non-uniformSiOxCyHz thin films using phase-modulated ellipsometry.

MOVPE에 의한 GaN 피라미드 꼭지점 위의 반극성 나노/마이크로 크기의 GaN 성장

We report on the growth and characterization of nano and micro scale GaN structures selectively grown on the vertex of hexagonal GaN pyramids. near the vertex of hexagonal GaN pyramids was removed by optimized photolithgraphy process and followed by a selective growth of nano and micro scale GaN structures by metal organic vapor phase epitaxy (MOVPE). The pyramidal GaN nano and micro structures which have crystal facets of semi-polar {1-101} facets were formed only on the vertex of GaN pyramids and the size of the selectively grown nano and micro GaN structures was easily controlled by growth time. As a result of TEM measurement, Reduction of threading dislocation density was conformed by transmission electron microscopy (TEM) in the selectively grown nano and micro GaN structures. However, stacking faults were newly developed near the edge of film because of the roughness and nonuniformity in thickness of the film.

Measurement of the thickness distribution and optical constants of non-uniform thin films

In this paper, an original method for the complete optical characterization of thin films exhibiting area thickness non-uniformity is presented. This method is based on interpreting experimental data obtained using an original imaging spectroscopic photometer operating in the reflection mode at normal incidence of light. A CCD camera is employed as a detector of the photometer. The spectral dependences of the reflectance measured simultaneously by individual pixels of the CCD camera correspond to the local reflectance of small areas of the non-uniform thin films characterized. These areas form a matrix along a relatively large part of the substrate covered with the non-uniform film. The spectral dependences of the local reflectance measured by the individual pixels are treated separately by means of the formulae for the reflectance valid for uniform thin films. The reason is that the local areas corresponding to the pixels are sufficiently small so that the film characterized can be considered to be uniform within these local areas. Using this approach, it is possible to determine the values of the local thickness and local optical constants for every small area of the matrix. Thus, in principle it is possible to determine the distributions (maps) of the local thickness and the local optical constants of the non-uniform films simultaneously. This method is used to characterize carbon-nitride thin films exhibiting only the thickness area non-uniformity.