Monte Carlo simulation of scanning electron microscope signals for lithographic metrology

Two computer codes for simulating the backscattered, transmitted, and secondary-electron signals from targets in a scanning electron microscope are described. The first code, MONSEL-II, has a model target consisting of three parallel lines on a three-layer substrate, while the second, MONSEL-III, has a model target consisting of a two-by-two array of finite lines on a three-layer substrate. Elastic electron scattering is determined by published fits to the Mott cross section. Both plasmon-generated electrons and ionized valence electrons are included in the secondary production. An adjustable quantity, called the residual energy loss rate, is added to the formula of Joy and Luo to obtain the measured secondary yield. The codes show the effects of signal enhancement due to edge transmission, known as blooming, as well as signal reduction due to neighboring lines, known as the “black-hole” effect.     

基于DSP的语音识别系统及其结构

介绍了一种基于TMS320C54xxDSP的语音识别系统及语音端点检测的过程,以及隐尔马柯夫模型（HMM）运用到语音识别的基本原理.最后介绍了TMS320C54xxDSP芯片的一些特点,同时也展现了语音识别技术在今后日常生活中的前景和用途.     

Aspects regarding measurement of thickness of intergranular glassy films

Materials such as Si₃N₄, SiC and SrTiO₃ can have grain boundaries characterized by the presence of a thin intergranular amorphous film of nearly constant thickness, in some cases (e.g. Si₃N₄) almost independent of the orientation of the bounding grains, but dependent on the composition of the ceramic. Microscopy techniques such as high‐resolution lattice fringe imaging, Fresnel fringe imaging and diffuse dark field imaging have been applied to the study of intergranular glassy films. The theme of the current investigation is the use of Fresnel fringes and Fourier filtering for the measurement of the thickness of intergranular glassy films. Fresnel fringes hidden in high‐resolution micrographs can be used to objectively demarcate the glass–crystal interface and to measure the thickness of intergranular glassy films. Image line profiles obtained from Fourier filtering the high‐resolution micrographs can yield better estimates of the thickness. Using image simulation, various kinds of deviation from an ideal square‐well potential profile and their effects on the Fresnel image contrast are considered. A method is also put forth to objectively retrieve Fresnel fringe spacing data by Fourier filtering Fresnel contrast images. Difficulties arising from the use of the standard Fresnel fringe extrapolation technique are outlined and an alternative method for the measurement of the thickness of intergranular glassy films, based on zero‐defocus (in‐focus) Fresnel contrast images is suggested. The experimental work is from two ceramic systems: Lu‐Mg‐doped Si₃N₄ and SrTiO₃ (stoichiometric and nonstoichiometric). Further, a comparison is made between the standard high‐resolution lattice fringe technique, the standard Fresnel fringe extrapolation technique and the methods of analyses introduced in the current work, to illustrate their utility and merits. Taking experimental difficulties into account, this work is intended to be a practical tool kit for the study of intergranular glassy films.     

Off-axis electron holography of electrostatic potentials in unbiased and reverse biased focused ion beam milled semiconductor devices

Off‐axis electron holography in the transmission electron microscope (TEM) is used to measure two‐dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p–n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed.     

Automatic TEM image alignment by trifocal geometry

Here we propose a novel method for automatic, markerless, feature‐based alignment of TEM images suitable for electron tomography. The proposed method, termed trifocal alignment, is more accurate than the previous markerless methods. The key components developed are: (1) a reliable multi‐resolution algorithm for matching feature points between images; (2) a robust, maximum‐likelihood‐based estimator for determining the geometry of three views – the trifocal constraint – required for validating the correctness of the matches; and (3) a robust, large‐scale optimization framework to compute the alignment parameters from hundreds of thousands of feature point measurements from a few hundred images. The ability to utilize such a large number of measurements successfully compensates for point localization errors. The method was experimentally confirmed with electron tomography tilt series of biological and material sciences samples, consisting of from 40 to 150 images. The results show that, with this feature‐based alignment approach, a level of accuracy comparable with fiducial marker alignment can be achieved.     

Freeze-fracturing for conventional and field emission low-temperature scanning electron microscopy: the scanning cryo unit SCU 020

A dedicated cryopreparation system, the SCU 020 (Balzers), is introduced and described in detail for use in low-temperature scanning electron microscopy (LTSEM). The basic unit consists of two parts: (i) a high-vacuum preparation chamber equipped with a cold-stage, motor-driven fracturing microtome, planar magnetron (PM) sputter source, quartz-crystal thin-film monitor, Meissner cold trap, and turbo molecular pump stand; and (ii) a second part (separated from the first by a sliding, high-vacuum valve) residing in the SEM chamber. This is equipped with an anti-contamination cold trap, a fully movable goniometer cold stage (having motor drives for x, y, and rotation) and replaces the SEM's original stage (Raith). The SCU 020 is entirely self contained allowing independence from, and synchroneity with, the SEM of choice. LTSEM micrographs of specimen (that are fully frozen hydrated or partially freeze-dried) surfaces or fracture faces, without or with various metal coatings, can be examined over a broad temperature range (-150 to +50°C). This is made possible by the combined application of the two, independently controlled, cold stages and the on-line, high-vacuum, specimen cryo transfer between them. In-situ etching is simple and straightforward. Intramembranous particles and membrane fracture steps, typically imaged in transmission electron microscopy (TEM), are resolved by PM sputtering with platinum at low specimen temperature and high-resolution LTSEM in a field emission microscope.     

基于CSI的轻量级自适应井下定位算法

针对传统井下定位成本高、工作危险系数大的问题,提出一种基于信道状态信息(channel state information, CSI)的轻量级自适应井下定位(lightweight self-adaptive underground positioning algorithm, LSA)方法。LSA方法以细粒度的CSI替代粗粒度的接收信号强度(received signal strength indicator, RSSI)来获得更高的定位精度,采用逆傅里叶变换将原始CSI数据转换为信道脉冲响应,以此选取视距信号,并通过构建CSI视距信号衰减模型实现轻量级的精确测距;基于井下现有WiFi网络中的访问接入点(access points, APs)位置和井下巷道特征,计算目标相对AP的方向,根据方向和测距结果完成定位。该方法能够自适应于AP在巷道中的任意位置部署,并利用拐角识别优化算法进一步提高定位的精度。试验结果表明,该方法能够使得定位中位数误差达到0.53 m,且无需在井下单独部署任何定位系统,性能明显优于已提出的CDPF、FILA等其他定位算法。     

基于数学解析法的油纸绝缘参数辨识研究

现阶段变压器油纸绝缘等效弛豫机构参数辨识多采用拓扑支路数任意假定、粒子群等智能算法对 N组非线性方程组寻优迭代计算。其计算往往具有收敛性差、结果不唯一等问题,且难以从介质响应函数特性分析真实的油纸绝缘弛豫过程,影响后续弛豫参数对老化评估的准确性。基于此,提出一种应用数学解析法的变压器油纸绝缘弛豫机构参数辨识新方法。首先,从介质响应函数特性出发,深入挖掘弛豫项数信息,辨识油纸绝缘等效弛豫机构的拓扑结构;其次,公式推演得到参数辨识的数学计算公式,避免了智能算法对非线性方程组的寻优误差与不唯一性;最后,通过实例验证该方法的有效性与可行性,提出的数学解析法可为变压器油纸绝缘介质内部弛豫响应特性提供可靠的数学分析模型。     

微型机械的研究现状及其产业化分析

微型机械是在微电子工艺的基础上发展起来的多学科交叉的前沿研究领域，具有广阔的应用前景。文 中分析了微型机械的研究发展现状，并对其市场前景进行预测。提出微型机械技术产品产业化是微技 术发展的必然趋势，在我国实现微型机械的产业化具有一定的可行性和必要性。最后，对于产业化过程 中的一些相关问题提出相应的对策。     

Electron energy loss spectroscopy for analysis of inhaled ultrafine particles in rat lungs

Epidemiologic studies have associated cardiovascular morbidity and mortality with ambient particulate air pollution. Particles smaller than 100 nm in diameter (ultrafine particles) are present in the urban atmosphere in very high numbers yet at very low mass concentration. Organs beyond the lungs are considered as targets for inhaled ultrafine particles, whereby the route of particle translocation deeper into the lungs is unclear. Five rats were exposed to aerosols of ultrafine titanium dioxide particles of a count median diameter of 22 nm (geometric standard deviation, GSD 1.7) for 1 hour. The lungs were fixed by intravascular perfusion of fixatives immediately thereafter. TiO(2) particles in probes of the aerosol as well as in systematic tissue samples were analyzed with a LEO 912 transmission electron microscope equipped with an energy filter for elemental microanalysis. The characteristic energy loss spectra were obtained by fast spectrum acquisition. Aerosol particles as well as those in the lung tissue were unambiguously identified by electron energy loss spectroscopy. Particles were mainly found as small clusters with a rounded shape. Seven percent of the particles in the lung tissue had a needle-like shape. The size distribution of the cluster profiles in the tissue had a count median diameter of 29 nm (GSD 1.7), which indicates no severe clustering or reshaping of the originally inhaled particles. Electron energy loss spectroscopy and related analytical methods were found to be suitable to identify and localize ultrafine titanium dioxide particles within chemically fixed and resin-embedded lung tissue.