Monte Carlo simulation of charging effects on linewidth metrology

Charging effects of scanning electron microscopes on the linewidth metrology of polymethylmethacrylate (PMMA) insulatorpatterns are investigated using Monte Carlo simulation. It is first revealed in detail how the nonunity yield of electron generation in the PMMA target leads to local charge accumulation and affects the image profile of secondary electrons as charging develops. Then the measurement offset due to charging effects is identified for various target patterns of isolated and array types. Finally, it is concluded that the measurement uncertainty caused by the measurement offset exceeds the error budget limit that will be allowed in the linewidth metrology of the next generation of semiconductors.     

The relationship between accelerating voltage and electron detection modes to linewidth measurement in an SEM

The basic premise underlying the use of the scanning electron microscope (SEM) for linewidth metrology in semiconductor research and production applications is that the video image acquired, displayed, analyzed, and ultimately measured accurately reflects the structure of interest. However, it has been clearly demonstrated that image distortions can be caused by the detected secondary electrons not originating at the point of impact of the primary electron beam and by the type and location of the secondary electron detector. These effects and their contributions to the actual image or linewidth measurement have not been fully evaluated. Effects due to uncertainties in the actual location of electron origination do not affect pitch (line center-to-center or similar-edge-location-to-similar-edge-location spacing) measurements as long as the lines have the same edge geometries and similar profiles of their images in the SEM. However, in linewidth measurement applications, the effects of edge location uncertainty are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of the errors introduced by beam/specimen interactions and the mode of signal detection at a variety of beam acceleration voltages and to discuss their relationship to precise and accurate metrology.     

基于AFM的纳米尺度线宽计量模型及其算法的研究

纳米尺度线宽的测量广泛应用于半导体制造、数据存储、微机电系统等领域。随着制造技术的进步,线宽的极限尺寸也变得越来越小,目前已经缩小至100 nm左右。在这一尺度范围内,由于样本制造技术的限制和测量仪器的影响,目前很难得到准确的测量结果。为了获得样本的真实几何尺寸信息,剔除测量方法和仪器本身对测量结果的影响,建立了一个基于AFM测量技术的线宽计量模型和相应算法。该模型将被测样本的截面轮廓用20个关键点分成5个部分共19段,用基于最小二乘的直线来拟合实际轮廓。应用该模型和算法可以分别得到单刻线轮廓拟合前后的顶部线宽b_T、b_(TF),中部线宽b_M、b_(MF),底部线宽b_B、b_(BF),左右边墙角A_L、A_R,以及高度h_。使用NanoScope Ⅲa型AFM对一个单晶硅(Si)线宽样本进行了测量,测量结果表明该模型和算法可以满足纳米尺度线宽计量的基本要求。     

Characterization of nitride thin films by electron backscatter diffraction

Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light‐emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality. In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1° towards [101 0]_GaN), where the tilt is due to the inclination of the sapphire substrate (cut off‐axis by 10° from (0001)_sapphire towards (101 0)_sapphire). We compare EBSD patterns obtained from As‐doped GaN films grown by plasma‐assisted molecular beam epitaxy (PA‐MBE) with low and high As₄ flux, respectively. Higher As₄ flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.     

Monte Carlo study for correcting the broadened line-scan profile in scanning electron microscopy

Line-scan profile is always broadened due to the probe shape of the primary electron (PE) beam in scanning electron microscopy (SEM), which leads to an inaccurate dimension metrology. Currently, the effective electron beam shape (EEBS) is suggested as the broadening function to overcome this issue for theoretical analysis, rather than the widely used Gaussian profile. However, EEBS is almost impossible to be acquired due to it strongly depends on both the sample topography and the electron beam focusing condition, which makes it is impossible to be applied in practical analysis. Taking the case of gate linewidth measurement, an approach is proposed to find a best-fit traditional Gaussian profile, which can optimally replace the EEBS in the case of the same sample structure and experimental condition for construction of a database of the parameter in traditional Gaussian profile. This approach is based on the use of the ideal and broadened line-scan profiles which are both obtained from Monte Carlo (MC) simulation, but respectively by an ideal and a focusing incident electron beam model. The expected value of parameter can be obtained through deconvoluting (here using a maximum-entropy algorithm) the broadened line-scan profile then fitting it to the ideal profile. Experimenters can benefit from this database to obtain true line-scan profiles for accurate gate linewidth measurement. This work should prove useful for samples of other structures and be an extension of the database in the future.     

Atom-probe for FinFET dopant characterization

With the continuous shrinking of transistors and advent of new transistor architectures to keep in pace with Moore's law and ITRS goals, there is a rising interest in multigate 3D-devices like FinFETs where the channel is surrounded by gates on multiple surfaces. The performance of these devices depends on the dimensions and the spatial distribution of dopants in source/drain regions of the device. As a result there is a need for new metrology approach/technique to characterize quantitatively the dopant distribution in these devices with nanometer precision in 3D.In recent years, atom probe tomography (APT) has shown its ability to analyze semiconductor and thin insulator materials effectively with sub-nm resolution in 3D. In this paper we will discuss the methodology used to study FinFET-based structures using APT. Whereas challenges and solutions for sample preparation linked to the limited fin dimensions already have been reported before, we report here an approach to prepare fin structures for APT, which based on their processing history (trenches filled with Si) are in principle invisible in FIB and SEM. Hence alternative solutions in locating and positioning them on the APT-tip are presented. We also report on the use of the atom probe results on FinFETs to understand the role of different dopant implantation angles (10° and 45°) when attempting conformal doping of FinFETs and provide a quantitative comparison with alternative approaches such as 1D secondary ion mass spectrometry (SIMS) and theoretical model values.     

Improving the quality of electron backscatter diffraction (EBSD) patterns from nanoparticles

In this study, we investigated the relative contributions of atomic number (Z) and density (ρ) to the degradation of the electron backscatter diffraction (EBSD) pattern quality for nanoparticles < 500 nm in diameter. This was accomplished by minimizing the diffuse scattering from the conventional thick mounting substrate through the design of a sample holder that can accommodate particles mounted on thin‐film TEM substrates. With this design, the contributions of incoherently scattered electrons that result in the diffuse background are minimized. Qualitative and quantitative comparisons were made of the EBSD pattern quality obtained from Al₂O₃ particles approximately 200 nm in diameter mounted on both thick‐ and thin‐film C substrates. For the quantitative comparison we developed a ‘quality’ factor for EBSD patterns that is based on the ratio of two Hough transforms derived from a given EBSD pattern image. The calculated quality factor is directly proportional to the signal‐to‐noise ratio for the EBSD pattern. In addition to the comparison of the thick and thin mounting substrates, we also estimated the effects of Z and ρ by comparing the EBSD pattern quality from the Al₂O₃ particles mounted on thin‐film substrates with the quality of patterns obtained from Fe–Co nanoparticles approximately 120 nm in diameter. The results indicate that the increased background generated in EBSD patterns by the electrons escaping through the bottom of the small particles is the dominant reason for the poor EBSD pattern quality from nanoparticles < 500 nm in size. This was supported by the fact that we were able to obtain usable EBSD patterns from Al₂O₃ particles as small as 130 nm using the thin‐film mounting method.     

New technique for in-situ measurement of backscattered and secondary electron yields for the calculation of signal-to-noise ratio in a SEM

The quality of an image generated by a scanning electron microscope is dependent on secondary emission, which is a strong function of surface condition. Thus, empirical formulae and available databases are unable to take into account actual metrology conditions. This paper introduces a simple and reliable measurement technique to measure secondary electron yield (δ) and backscattered electron yield (η) that is suitable for in-situ measurements on a specimen immediately prior to imaging. The reliability of this technique is validated on a number of homogenous surfaces. The measured electron yields are shown to be within the range of published data and the calculated signal-to-noise ratio compares favourably with that estimated from the image.     

A precision desktop plate-to-roll apparatus for development of advanced flexographic printing processes

Flexographic printing, which involves high-speed contact of an inked stamp against a substrate, is of increasing interest for scalable manufacturing of electronics in new formats. However, the adaptation of flexography to thinner, finer features which are generally required for printed electronics requires improved understanding of stamp-substrate contact mechanics. Here, we present a desktop plate-to-roll (P2R) printing apparatus which enables the study of flexographic printing in a semi-continuous format that mimics industrial printing. In particular, we tailor the specifications of the machine to use nanoporous stamps which have been shown to enable flexographic printing of ultrathin ink features with micron-scale linewidth. Printing with nanoporous stamps requires precise control of stamp-substrate contact force (2–250 mN) and elimination of shear force at the interface among others; these are accomplished using a flexure-supported substrate, and by coordinated rotary-linear motion of the system. We detail the design and evaluation of the P2R machine and demonstrate printing of high-resolution features (<3 μm line width) with nanoporous stamps at speeds of up to 0.2 m/s.     

Quick determination of included angles distribution for miscut substrate

A simple method which can be performed with general laboratory facility is described for quickly determining the included angles distribution (including miscut angle) between the crystal plane and sample plane for a miscut substrate. This method is based on the rocking curve measurement of High-resolution X-ray diffraction (HRXRD). After easily measuring and calculating values of two included angles (θ₁ and θ₂) between the crystal plane and sample plane at two arbitrary mutually perpendicular azimuths of the sample plane by HRXRD, all included angles at arbitrary azimuths of the miscut substrate can be quickly calculated. Further, the value of miscut angle (θ_max) can be determined and its specific azimuth position on sample plane can be also easily found. Besides, since original azimuthal measurements of θ₁ and θ₂ may be situated on different positions of the sample plane, the possible condition is finally classified as four types. And then, the curves of miscut angle and azimuthal orientation under four different conditions are described in detail, respectively and their computational formulas are also distinguished carefully.     

Photovoltaic module performance measurements traceability: Uncertainties survey

The performance of a photovoltaic module is mainly defined by the maximum power P_max, which is measured under standard conditions (1000 W/m², AM 1.5, 25 °C) using a sunlight (natural or simulated) and a calibrated reference device. This reference photovoltaic device, placed in the same lighting conditions than the module under test, allows the measurement of the sunlight levels through the monitoring of the maximum power of these devices. As a key metric for photovoltaics economy, the measurement of P_max must be a subject of a strong attention. This paper describes the metrology applied and the typical levels of uncertainties achievable by National Laboratories as well as in the Industry.     

Diffraction patterns of artificial two-dimensional crystals synthesized in situ in an environmental scanning transmission electron microscope

In this study, we demonstrated the use of electron‐beam‐induced deposition for synthesis of artificial two‐dimensional crystals with an in situ scanning transmission electron microscope. The structures were deposited from W(CO)₆ in an environmental scanning transmission electron microscope on a 30‐nm‐thick Si₃N₄ substrate. We present clear electron beam diffraction patterns taken from those structures. The distance between the diffraction peaks corresponded to the dot spacing in the self‐made surface crystal. We propose using these arrays of dots as anchor points for making artificial crystals for diffraction analysis of weakly scattering or beam‐sensitive molecules such as proteins.     

Fabrication of ball-shaped atomic force microscope tips by ion-beam-induced deposition of platinum on multiwall carbon nanotubes

Ball-shaped atomic force microscope (AFM) tips (ball tips) are useful in AFM metrology, particularly in critical dimension AFM metrology and in micro-tribology. However, a systematic fabrication method for nano-scale ball tips has not been reported. We report that nano-scale ball tips can be fabricated by ion-beam-induced deposition (IBID) of Pt at the free end of multiwall carbon nanotubes that are attached to AFM tips. Scanning electron microscopy and transmission electron microscopy analyses were done on the Pt ball tips produced by IBID in this manner, using ranges of Ga ion beam conditions. The Pt ball tips produced consisted of aggregated Pt nano-particles and were found to be strong enough for AFM imaging.     

Polymer Jet Printing of SU-8 Micro-Dot Patterns on Si Surface: Optimization of Tribological Properties

Tribological properties of optimized SU-8 patterns (micro-dots with varying pitch) on Si (silicon) were evaluated using a ball-on-disk tribometer. Sliding tests on the patterns were conducted against a 2-mm diameter Si₃N₄ ball at varying normal loads and sliding velocities. It was observed that the pitch of the SU-8 pattern on Si substrate had a significant effect on the initial coefficient of friction and wear durability. Initial coefficient of friction studies have concluded that the SU-8 polymeric micro-dots improved the tribological properties by sharing the normal force and reducing the contact area. For the wear durability test, ultra-thin layer of perfluoropolyether was over-coated onto SU-8 micro-dot specimens, and the optimized pitch specimens have shown wear durability of more than 100,000 cycles at a normal load of 350 mN.     

A study of geometric and true levelling in electroplating using stylus methods

Under suitable conditions the process of electroplating improves the surface characteristics of the workpiece. This effect is called levelling and arises from two fundamental mechanisms: (i) geometric levelling and (ii) true levelling. Assessment of percentage levelling using surface profilometry (R_a) is well established. However, the present work suggests that the use of more complex surface parameters obtained by digital surface metrology gives a better understanding of the mechanisms involved. Since the techniques are both quick and reliable they should form a major tool in the development of plating solutions and the establishment of the optimum plating conditions. The relations between the original surface finish R_a, the average surface slope and the levelling achieved for varying plating thicknesses with geometric levelling and combinations of geometric and true levelling are discussed. Finally some preliminary results are reported for computer simulations of geometric and true levelling of actual surfaces.     

The Influence of W-DLC and CrxN Thin Film Coatings on Impact Damage between Bearing Materials

In this work, the effect of hard tribological coatings was studied in terms of mitigating impact damage between tungsten carbide spherical elements and two different types of steel substrates. The coatings included a hard, highly elastic Tungsten-incorporated diamond-like carbon (W-DLC) coating at two different thicknesses and a harder, less elastic Cr_xN coating. Impacts were created using a drop-test rig described herein and characterized in three ways: a measure of the coefficient of restitution during impact, investigation of the impact site using an optical interferometer, and fixed ion beam cross sections of select impacts for observation of subsurface damage within the coating and substrate. It was found that hard coatings on softer substrates such as 440C steel were able to mitigate surface damage up to a certain impact speed, depending on the coating, but were unable to influence the coefficient of restitution. On harder substrates like 52100 alloy steel, the coatings were found to increase the coefficient of restitution, indicating a reduction in energy loss due to plastic deformation, and to reduce damage at each tested speed. These effects and their potential influence on bearing performance are discussed in regard to impact mechanics, surface metrology, and the material properties of the coating and substrate acquired by nanoindentation.     

Fabrication of resistance type humidity sensor based on CaCu3Ti4O12 thick film

A resistance type humidity sensor has been fabricated from an assembly of CaCu₃Ti₄O₁₂ thick film, Ag interdigitated electrodes, and an Al₂O₃ ceramic substrate. The humidity sensing properties were measured using the direct current (DC) analysis method. The results show that the electrical properties of the CaCu₃Ti₄O₁₂ thick film are dependent on humidity and applied voltage. At low humidity, the film exhibited low conductivity and behaved as an insulator. However, at high humidity, the conductivity of the film increased due to the enhancement of ion conduction. These outcomes indicate that the measured resistance is highly dependent on the applied bias voltage within the whole humidity range i.e. 20–90% relative humidity (RH) at ambient temperature. The response and recovery times as well as sensitivity were determined to be around 2.8 min, 25 min, and 98.2%, respectively. Therefore, it is concluded that CaCu₃Ti₄O₁₂ thick film has good humidity sensing properties and has high potential in the application for fabrication of high-performance humidity sensors.     

High-resolution transmission electron microscopy of inorganic materials in cellular and topological random systems

The structure of amorphous Se films, in the topological random system, has been studied by the computer-simulation, electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). As an example of HRTEM of the cellular random system, our recent investigation on Ba-ferrites is reviewed beforehand. In HRTEM images of spin-glass BaTi_2–xSn_xFe₄O₁₁ (x < 0.6), magnetic clusters or clusters of FeO₆-octahedra surrounded by TiO₆-octahedra have been found. The structure of BaSn₂Fe₄O₁₁ (x = 2) has been determined. The ordering of Sn (Ti) and Fe ions increases with increasing x, which interprets the change from the spin-glass state to nonspin-glass state at x = 0.6. It is shown that a cluster of polarized lattice ions is detectable in images of polar-glass Ba_xK_2–xFe_xTi_6–xO₁₃ (x ≥ 1.2). The structure models of amorphous Se films forming on a substrate have been constructed on a computer, and their radial distribution function (RDF) and HRTEM images have been calculated. Experimental RDF and HRTEM images have been obtained from vacuum-deposited amorphous Se films and are compared with the calculated ones. It is concluded that in the as-deposited films most of Se molecules may be composed of Se atoms as small as three and that by the electron-beam irradiation the molecules link to form spiral chains in amorphous state and then arrange to have the hexagonal crystal structure.     

Tribological and mechanical investigation of SiO2 and Si3N4 coatings on fused silica and borosilicate glass

Amorphous SiO₂ and Si₃N₄ plasma‐enhanced chemical vapour deposited (PECVD) coatings were deposited on two different substrate materials (fused silica and borosilicate glass), with three coating thicknesses (0.1, 0.5, and 1.0 μm). The mechanical properties (hardness and elastic modulus) were determined by depth‐sensing indentation, with loads from 700 mN down to 0.1 mN. Tribological behaviour was studied in instrumented oscillating sliding tests at room temperature with a ball‐on‐flat arrangement, in which the coated disc was tested against an alumina ball, at a load of 1 N. Interpretation of the measurement of hardness and modulus of the coatings has to take into consideration the influence of layer thickness and the effect of the substrate. Tensile film stress and crack generation were only observed for Si₃N₄ on fused silica above a threshold thickness. Friction and wear measurements show that the coating has an effect on friction, while wear is affected by the thin coatings only for a short running‐in phase. The morphology of the wear scars indicates that the coatings have good adhesion. Despite crack generation, delamination effects were not observed. Indentation patterns similarly showed excellent lateral homogeneity of the mechanical properties over the entire film surface, and indicated that load‐displacement curves may be used to characterise the system.