An automated image alignment system for the scanning electron microscope

We have developed an automated image alignment system for the scanning electron microscope (SEM). This system enables specific locations on a sample to be located and automatically aligned with submicron accuracy. The system comprises a sample stage motorization and control unit together with dedicated imaging electronics and image processing software. The standard SEM sample stage is motorized in the X and Y axes with stepping motors which are fitted with rotary optical encoders. The imaging electronics are interfaced to beam deflection electronics of the SEM and provide the image data for the image processing software. The system initially moves the motorized sample stage to the area of interest and acquires an image. This image is compared with a reference image to determine the required adjustments to the stage position or beam deflection. This procedure is repeated until the area imaged by the SEM matches the reference image. A hierarchical image correlation technique is used to achieve submicron alignment accuracy in a few seconds. The ability to control the SEM beam deflection enables the images to be aligned with an accuracy far exceeding the positioning ability of the SEM stage. The alignment system may be used on a variety of samples without the need for registration or alignment marks since the features in the SEM image are used for alignment. This system has been used for the automatic inspection of devices on semiconductor wafers, and has also enabled the SEM to be used for direct write self-aligned electron beam lithography.     

Design of orientation stages for step and flash imprint lithography

This paper presents the design of orientation stages for high-resolution imprint lithography machines. These machines implement a new lithography process known as Step and Flash Imprint Lithography (SFIL) and are intended for 1) sub 100 nm imprint demonstrations on flat substrates and 2) investigation of potential defect propagation during step and repeat imprinting. SFIL is an imprint lithography process that is a combination of chemical and mechanical steps and its implementation at room temperature and low pressure makes it an attractive process as compared to other imprint techniques. A critical component of an imprint machine is the orientation stage that is required to provide uniform intimate contact between the template and substrate surfaces. The orientation stage requirements are distinct from those used in photolithography since the depth of focus of projection optics allows for larger errors in the orientation alignment. Also, due to contact between the template and substrate surfaces in imprint lithography, the separation kinematics must be carefully controlled in the SFIL process. Two different orientation stages are designed for single- and multi-imprint machines. In order to eliminate the particle contamination due to frictional contacts, all joints are made with flexure joints. Imprint experiments have been performed to demonstrate sub 100 nm imprints.     

纳米硬度计研究多晶硅微悬臂梁的弹性模量

利用纳米硬度计通过微悬臂梁的弯曲试验来测量其力学特性是一种简便而有效的方法,具有很高的载荷分辨率,可精确测量微悬臂梁纳米级弯曲形变。运用该方法在研究微悬臂梁的弯曲形变过程中,必须考虑压头在微悬臂梁上的压入以及微悬臂沿宽度方向的挠曲。微悬臂梁采用普通的集成电路工艺(IC)制造。试验研究表明,多晶硅微悬臂梁的纯挠曲与载荷成很好的线性关系,呈现弹性变形,通过该线性关系可计算得到梁的弹性模量。测得的多晶硅微悬臂梁的弹性模量为156±(2.9%-6.3%)GPa。     

蓝宝石镀膜方法研究

蓝宝石具有一系列优异的光学和力学性能,使其在现代镀膜领域中倍受青睐。在一些高科技领域中,蓝宝石作为重要的功能材料,为实现不同的功能,选择不同的镀膜材料来实现。介绍了蓝宝石的主要物理性能,并对其作为衬底的几种镀膜方法作了简单介绍,包括磁控溅射法、脉冲激光沉积法、金属有机化学气相沉积法、电子柬蒸发法。     

MECHANICAL DEFLECTION OF POLYSILICON MICROCANTILEVER BEAMS USING NANOINDENTATION

0INTRODUCTIONThe miniaturization of microelectronic device is now reaching the mechanical field, allowing the integration of micromechanisms together with their operation electronics in a single device. This leads to interesting perspectives in the design of monolithic microrobtic systems by the micromachining techniques directly derived from standard silicon technology. Scientists have already moved MEMS into various stages of conception and development for making laboratories on chips,…     

微电子机械系统中典型构件的力电耦合分析及其应用研究

力电耦合是大多数微电子机械系统（尤其是以静电驱动的微机械）的重要特征。文中采用有限元（FEM）结合边界元（BEM）的方法来混合求解MEMS中的力电耦合问题,利用自行研制的程序给出了几种典型构件（平行板、悬臂梁和固支梁）的分析结果,并同其他商业软件（ANSYS和Intelisuite）的计算结果进行了比较。同时,还将这种分析方法应用到微继电器的设计和MEMS构件残余应力的检测中。     

关于夹芯梁四点弯曲试验的计算分析

在材料力学推导出的矩形截面梁剪应力公式基础上,利用夹芯梁轴向位移,弯曲挠度与剪切应变的几何关系,推导出了夹芯梁截面弯曲应力及弯曲挠度表达式,弹性理论及有关试验结果都证明了该方法的计算精确度较高.理论计算分析表明:外载荷作用下夹芯梁四点弯曲时,在外载荷作用处夹芯梁面板与芯材结合部位应采用强度理论进行校核;均布载荷作用下剪...     

Dynamic plastic behavior of a free–free beam striking the mid-span of a clamped beam with shear and membrane effects considered

Recently Yu et al. (Int. J. Solids Struct. 38 (2001) 261) made a study on the dynamic behavior of a flying free–free beam striking the tip of a cantilever beam using the rigid, perfectly plastic (r-p-p) material model. Later, also based on the r-p-p material model Yang and Yu (Mech. Struct. Mach. 29 (2001) 391) analyzed another impact problem of a free rotating hinge beam striking a cantilever beam. Both of these studies ignored the finite deflection effects on the plastic behavior of the colliding beams. However if the free–free beam strikes a clamped beam, the influence of finite-deflections, or, geometric changes, must be retained in the governing equation if the maximum permanent transverse displacement of the clamped beam exceeds the corresponding beam thickness. The problem becomes more interesting since the deformation mechanisms of the beam system and the partitioning of energy dissipation in the beams are significantly different from those predicted by ignoring the influence of membrane forces. Accordingly the failure modes of the structure are different.In the present paper, a theoretical model based on the r-p-p material idealization is proposed to simulate the dynamic behavior when the mid-point of a translating free–free beam impinging on the mid-span of a clamped beam with the beam axes perpendicular to each other. The plastic behavior of the beam system is explored with shear sliding and finite deflection effects taken into account. The final deflection, the dissipation of energy within the two beams after impact and the influence of the structural and material parameters are discussed. It is shown that membrane force plays an important role during the response process, especially when the deflection is of the same order as the thickness of the clamped beam.     

大型超静定回转窑支承系统等载荷调窑优化研究

通过对回转窑支承载荷分配进行分析，建立支承载荷求解的力学模型和线性方程组，导出支承载荷分配与支承偏差的关系式；以轴线调整量为优化变量，各档托轮的最大支承力最小为目标函数建立优化模型；结合现场实例进行支承系统等载荷优化调整研究，得出有益的结论。为回转窑的维护与调整提供理论依据，对现场生产有重要的指导意义。     

Analytical and experimental study of mismatch strain-induced microcantilever behavior during deposition

A model of mechanical behavior of microcantilever due to mismatch strain during deposition of MEMS structures is analytically derived and experimentally verified. First, a microcantilever, modeled as an Euler-Bernoulli beam, is subjected to deposition of another material and a linear ordinary differential equation which considers the throughthickness variation of the mismatch strain is derived. Second, the deposition analysis is experimentally verified by electroplating of nickel onto an AFM cantilever beam. The deflection of the AFM cantilever is measured in-situ as a function of the deposited thin film thickness through the optical method of Atomic Force Microscopy and the mismatch strain with the through-thickness variation is determined from the experiment results. The usefulness of these equations is that they are indicative of the real time behavior of the structures, i.e. it predicts the deflection of the beam continuously during deposition process.     

Effects of temperature on mechanical properties of SU-8 photoresist material

A representative fabrication processing of SU-8 photoresist, Ultraviolet (UV) lithography is usually composed of spin coat, soft bake, UV exposure, post exposure bake (PEB), development and optional hard bake, etc. The exposed region of SU-8 is crosslinked during the PEB process and its physical properties highly depend on UV exposure and PEB condition. This work was initiated to investigate if thermal baking after fabrication can affect the mechanical properties of SU-8 photoresist material because SU-8 is trying to be used as a structural material for MEMS operated at high temperature. Since a temperature of 95°C is normally recommended for PEB process, elevated temperatures up to 200°C were considered for the optional hard bake process. The viscoelastic material properties were measured by dynamic mechanical analyses (DMA). Also, pulling tests were performed to obtain Young’s modulus and Poisson’s ratio as a function of strain rate in a wide temperature range. From this study, the effects of temperature on the elastic and viscoelastic material properties of SU-8 were obtained.     

Absolute two-dimensional sub-micron metrology for electron beam lithography: A calibration theory with applications

A mathematical theory is presented along with some simple resulting procedures that permit an electron beam lithography machine to be calibrated by using it to make multiple observations of an imprecisely defined but stable planar object. The calibration thus obtained yields a degree of accuracy that is approximately equal to the reproducibility of the machine. For this purpose a rigid, movable grid plate is used, with grid points placed at arbitrary but more-or-less evenly distributed, fixed positions on its surface. An e-beam lithography machine with a high precision X-Y stage has been used to measure such a grid plate. Two interferometer beams, nominally parallel to the X- and Y-axes, measure stage displacements. No geometric assumptions are made concerning the stage, other than repeatability. Although the assumptions are very general, it is possible to observe the grid in just three orientations to determine both an inverse distortion function (calibration) and accurate, absolute rectangular coordinates for the grid points, providing that the absolute distance between a pair of points on the grid is known. A calibration program has been written applying the theory to the practical problem of calibrating an e-beam lithography system. Simulations based upon actual e-beam measurements confirm the theory for the practical situation. The paper concludes with suggestions for applictions to three other areas of science and technology: astronomy, optometry, and satellite geodesy.     

Comprehensive analysis of the influence of structural and dynamic parameters on the accuracy of nano-precision positioning stages

Nano-precision positioning stages are characterized by rigid-flexible coupling systems. The complex dynamic characteristics of mechanical structure of a stage, which are determined by structural and dynamic parameters, exert a serious influence on the accuracy of its motion and measurement. Systematic evaluation of such influence is essential for the design and improvement of stages. A systematic approach to modeling the dynamic accuracy of a nano-precision positioning stage is developed in this work by integrating a multi-rigid-body dynamic model of the mechanical system and measurement system models. The influence of structural and dynamic parameters, including aerostatic bearing configurations, motion plane errors, foundation vibrations, and positions of the acting points of driving forces, on dynamic accuracy is investigated by adopting the H-type configured stage as an example. The approach is programmed and integrated into a software framework that supports the dynamic design of nano-precision positioning stages. The software framework is then applied to the design of a nano-precision positioning stage used in a packaging lithography machine.     

纳米硬度技术在表面工程力学性能检测中的应用

结合纳米硬度技术测量各类薄膜和块体材料表层的纳米压痕硬度、弹性模量、断裂韧性、膜厚、微结构的弯曲变形，采用纳米划痕硬度技术测量各类薄膜和块体材料的粗糙度、临界附着力、磨擦系数、划痕横剖面。纳米硬度计是检测材料表层微米乃至几十纳米力学性能的先进仪器，可广泛应用于表面工程中的质量检测。     

分析梁大变形问题的一种新算法

梁发生大变形时,在变形前的平衡位置建立平衡方程必然引起很大误差,因此除了考虑位移与变形之间的非线性关系外,几何非线性问题还需要考虑大变形所引起的平衡方程的变化。文中提出了一种在变形后的平衡位置分析几何非线性梁的新算法,建立梁发生大变形一阶微分控制方程的矩阵形式,结合迭代修正齐次扩容精细积分法和迭代优化算法进行求解。由于考虑大变形（挠度和转角）对平衡方程的影响,文中方法的模型较为精确,采用精细积分法可以实现高精度求解。以悬臂梁为例,验证方法的正确性和精确性。其方法求解简单,对于不同的边界条件,只需修改优化目标函数。     

锥轴的切削变形计算与误差控制

为了计算锥形轴类零件的切削变形,推导出锥形变截面简支梁的弯曲变形通用表达式,应用C语言编程迅速求出最大变形量及最大变形位置。并用工艺参数控制法减少锥轴的切削变形误差,从而保证加工精度。     

考虑温度效应的两端固支微机电开关梁静力分析

建立考虑温度效应的二维两端固支微机电开关梁静力变形分析模型,利用该模型分析温度变化引起的失稳问题,并利用该模型对两端固支微开关梁受电场力和温度作用下的受力变形进行分析。分析过程分为三个阶段：梁受电场力和温度变化作用,而在梁中点不受任何约束的变形阶段;除受电场力和温度变化作用外,梁中点变形受约束,因而梁中点受支反力作用的变形阶段;梁受电场力、温度变化以及支反力作用,并且在梁的中间一段具有指定挠度和转角的变形阶段。第二阶段中支反力的大小以及第三阶段中支反力的大小和位置都同驱动电压和温度变化有关。在实例中,给出部分计算结果,包括：温度变化对不同阶段梁受力变形的影响、对吸合电压的影响、对微开关电容的影响,以及不同温度变化下梁长对吸合电压的影响和不同温度变化下梁高对吸合电压的影响等,从中可以看出温度变化的作用及考虑温度效应的必要性。     

Design of a contact probe with high positioning accuracy for plasmonic lithography

Plasmonic lithography with a contact probe records nano-meter scale features and has high-throughput owing to its capability to scan in contact mode. The probe is commonly based on a micrometer-scale cantilever, which leads to the tip-positioning problem due to force-deflection that induces lateral tip displacement. We propose a geometrically modified probe to achieve high positioning accuracy. Contrary to a conventional cantilever-tip probe, we designed a "circular probe" with arc-shaped arms that hold the tip in the center. The mechanism is based on the "fixed-fixed beam" concept in material mechanics. To confirm its positioning accuracy, we used a finite element method (FEM) to calculate the tip displacement for a circular probe and compared the results with those using a conventional cantilever-tip probe. The probe was designed considering a silicon-based micro-fabrication process. The designed probe has a square outline boundary with a length of 50 μm, four arms, and a pyramidal tip with a height of 5 μm. The ratio of the lateral tip displacement to the vertical deflection was evaluated to indicate the accuracy of the probe. The probe has higher positioning accuracy by a factor of 10(3) and 10 in its approach mode and scan mode, respectively, compared with a cantilever-tip probe. We expect that the probe is suitable for the applications that require high positioning accuracy, such as nanolithography in contact mode and applications based on multiple-probe arrays.     

New tribological strategies for cutting tools following nature

The material concept of animal teeth for cutting viscoelastic and abrasive food is completely different to those existing for industrial cutting tools. Biological cutting systems use abrasive wear in order to form sharp cutting edges. This work gives an overview of biological principles and describes a biomimetic approach for designing industrial cutting tools. The developed tools based on nature inspired hierarchic structure and shape show outstanding mechanical properties and provide evidence that self-sharpening effects and high abrasive resistance must not be contradicting.     

光刻机工件台宏动三自由度建模及自适应神经网络控制

提出了一种工件台宏动三自由度建模方法以解决光刻机工件台宏动部分在X和Y方向的运动耦合问题并实现它的超精密长行程微米精度的跟踪定位。该建模方法将X方向电机的偏转角度作为被控对象并且在模型中包含了耦合效应对X方向运动的影响。基于此模型提出了一种自适应神经网络控制策略,该策略采用径向基函数(Radial Basis Function,RBF)神经网络对模型参数信息及外界非线性扰动进行实时在线估计,以减小未建模动态、电机齿槽力波动、端部效应、摩擦等扰动对控制系统性能的影响。通过对控制策略的理论推导和稳定性分析,保证了闭环控制系统的收敛性。最后在光刻机工件台上进行了S曲线跟踪定位试验,验证了宏动三自由度建模方法和控制策略的效果。试验结果显示:X和Y方向的位置跟踪误差均小于3μm,X方向电机偏转角度小于1μrad,满足工件台宏动部分跟踪定位精度的要求。