叠栅条纹相位分布对对准精度的影响分析

光刻对准中,一般将硅片和掩模对准标记制作成周期接近的光栅,通过光栅标记叠加形成的叠栅条纹的相位信息,探测掩模和硅片的相对位置关系。在实际的应用中,叠栅条纹的方向不仅与对准标记的几何位置有关,而且还与CCD的位置有关。为了将叠栅条纹的光刻对准方法推向实际应用,从矩形光栅到叠栅条纹,分析了一般光栅的相位分布规律。根据叠栅条纹相位特性分析了掩模、基片和CCD的几何位置对对准精度的影响;建立了实际对准偏差与理论值的数学关系模型。研究表明,没有角位移的情况下,当位移值小于0.4pixel时,理论上最大对准误差低于0.002pixel。     

Reducing the stray light of holographic gratings by shifting the substrate a short distance in the direction parallel or perpendicular to the exposure interference fringes

This research proposes a simple and practical method to make low-stray-light gratings, where the substrate shifts about a 1 mm distance in the direction parallel or perpendicular to the exposure interference fringes. When the substrate shifts, a reference grating next to the substrate is used to adjust in real time the phase of the exposure interference fringes relative to the substrate. Shifting eliminates the exposure defects and therefore decreases the stray light of gratings. Several gratings are successfully made by using this method, which have straighter grooves,smoother surfaces, and lower stray light than gratings made in conventional interference lithography.     

Digital moiré fringe measurement method for alignment in imprint lithography

Accurate layer-to-layer alignment, which is of prime importance for the fabrication of multilayer nanostructures in integrated circuits, is one of the main obstacles for imprint lithography. Current alignment measurement techniques commonly involve an image detection process for coarse alignment followed by a grating interference process for fine alignment. Though this kind of two-level alignment system is reasonable for measurement, when it is used in real imprint lithography, it is inconvenient because of the existence of a complex loading system that needs space for alignment. In this study, we propose a fine alignment method using only image detection using grating images and digital moiré fringe technology. In this method, though the gratings are also selected as alignment marks for accurate measurement, they do not interfere with the physics. The grating images captured from the template and wafer are used to measure angular displacement and to form parallel digital moiré fringes. The relative linear displacement between the template and wafer is determined by detecting the spatial phase of parallel digital moiré fringes. Owing to the magnification effect of digital moiré fringes, this method is capable of generating accurate measurements. According to the experimental results, this digital moiré fringe technique is accurate to less than 10 nm. In addition, without a complex grating interference system, this method has the advantage of being easy to operate.     

Optical ultramicrometer technique utilizing a composite diffraction grating

Precise control of positioning or alignment technique utilizing a “composite diffraction grating” formed by superimposing a pair of gratings is proposed. Positioning accuracy of ±0.1 μm has been achieved in the preliminary experiments using dual transmission gratings. This indicates a novel method of sensitive detection of a displacement.     

Sensing Characteristics of A Precision Aligner Using Moire Gratings for Precision Alignment System

Sensing characteristics of a precision aligner using moire gratings for precision alignment sysem has been investigated. A differential moire alignment system and a modified alignment system were used. The influence of the setting accuracy of the gap length and inclination of gratings on the alignment accuracy has been studied experimentally and theoretically. Setting accuracy of the gap length less than 2.5μm is required in modified moire alignment. There is no influence of the gap length on the alignment accuracy in the differential alignment system. The inclination affects alignment accuracies in both differential and modified moire alignment systems.     

Sensing Characteristics of A Precision Aligner Using Moire Gratings for Precision Alignment System

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Method of making mosaic gratings by using a two-color heterodyne interferometer containing a reference grating

We propose and demonstrate a two-color heterodyne interferometric method for making a perfect mosaic of two planar gratings that can substitute for a single and larger grating without introducing wavefront aberration at any wavelength. The lateral and longitudinal phase errors are separated and eliminated by use of two wavelengths in the interferometry. The accuracy of the phase difference measurement is improved by this heterodyne scheme. The method ensures that the lateral gap between the two subaperture gratings is an integer multiple of the grating period. For a pair of 0.72 microm period gratings we experimentally achieved a lateral alignment error of less than 1% of the grating period.     

Measurement of elastic deformation of rotating objects by using holographic interferometry

Double-exposure holographic interferometry is applied to measure the elastic deformation of rotating objects. The first exposure is made in the rotating state and the second in the static state. The precise positioning of the object between the two exposures is obtained by using holographically produced Haidinger's fringes.     

Spectral polarization-dependent loss of cascaded long-period fiber gratings

We have measured the spectral polarization-dependent losses of cascaded long-period fiber gratings composed of single, double, and triple identical gratings and fabricated by exposure of a UV laser beam on one side of a fiber. The measurement was made by use of the Mueller matrix method for scanning the wavelength of the incident beam. The polarization-dependent loss was dramatically increased as the number of cascaded gratings was increased. The formation of the UV-induced geometric birefringence in the fiber grating and its relationship to the fine interference fringes formed by cascading gratings are discussed.     

高质量全息光栅的制作

全息光栅由感光版记录高斯光束干涉条纹制得 ,干涉条纹的不等宽性降低了光栅品质。制取高质量全息光栅的关键是要用均匀平面波作光源。在分析干涉区内光强分布的基础上 ,给出了制作等周期正弦全息光栅的两种方法 :限制曝光区大小的方法和高斯光束强度均匀化的方法。     

Control of anisotropic diffraction in liquid-crystal composite volume gratings

Orientation-controlled anisotropic diffraction gratings are realized by interferometric exposure using composite materials of nematic liquid crystals (LCs) and LC diacrylate monomers. The anisotropic diffraction properties in volume gratings, which dominantly diffract p- or s-polarized light, are shown to be controlled by the rubbed directions of the alignment layers under the control of the photopolymerization temperature. Images of the fringe patterns observed by polarization microscopy show the effects of the alignment layers on the LC orientation during grating formation.     

变线距光栅线密度的干涉测量

变线距光栅在同步辐射装置、激光核聚变装置上有着广阔的应用前景，它的制作和检测方法尚未成熟。用干涉法测量变线距光栅的线密度，给出了测量原理、实验中的光路、数据处理的方法、测量结果。在待测光栅表面，衍射光干涉条纹的数量和密度是入射光干涉条纹和倍增后光栅的刻线之差。采用共光路的方案，使光路具有很强的抗干扰能力。用中值滤波消除干涉图像中的干扰。针对不同的干涉条纹，讨论和比较了两种测量方法，提出相对密度不变性。证明了干涉法完全可以用于变线距光栅的线密度测量，并能达到一定的精度，初步解决了检测问题，认为这种方法也可以用于变线密度光栅的加工中。     

Experimental study of multiplexed holographic gratings recorded in a photopolymerizable silica glass

Recently the capability of photopolymerizable sol–gel materials to angular multiplex holographic gratings has been demonstrated [1, 2]. In this study, holographic transmission gratings were recorded using angular multiplexing in a silica glass doped photopolymer holographic recording material. The time interval between exposures and the angular selectivity were analyzed, in particular their effects on the dynamic range. By using the optimal parameters gratings of similar response were achieved with values of M/#=4.8, as well as good values of diffraction efficiency with high photosensitivity. PACS 42.40.Pa; 42.70.Ln     

Alignment on moiré fringes of finite width during optical processing of images of a periodic amplitude grating which are distorted by the reconstructed wave front

A method of alignment on moiré fringes of finite width for visualization of the deflection angles of rays reconstructed by a hologram of a phase object is described. It is suggested that the resulting moiré pattern be obtained by superposing two distorted images of amplitude gratings with different period. The result of an experimental test of the method is presented. Zh. Tekh. Fiz. 69, 130–132 (February 1999)     

Shifted-phase calibration for a 3-D shape measurement system based on orthogonal composite grating projection

This paper proposes a novel method for reducing measurement error caused by spectrum overlapping in orthogonal-composite-grating-based 3-D measurement method. For 3-D measurement systems based on orthogonal composite grating projection, spectrum overlapping causes phase of each deformed phase-shifting fringe changed differently, which violates the principle that the shifted phases between adjacent deformed fringes must be equivalent to 2π/3, and therefore results in phase measurement error. The proposed shifted-phase calibration method is based on that phase variation of each deformed fringe is independent of height and reflectivity of the measured object. Three composite gratings are projected on the reference plane, and each carrier channel includes three phase-shifting gratings needed in phase measuring profilometry (PMP). Because the adjacent phase-shifting fringes demodulated from the same carrier channel have the phase difference of 2π/3, we can respectively calculate the reference plane's phases of three carrier channels by the phase algorithm of PMP method, and the shifted phases between them are obtained. When an object is measured, the shifted phases between deformed phase-shifting fringes can be calibrated. A new 3-D measurement mathematical model is set to reconstruct object. Our experiments prove that the proposed method can effectively restrain the effect of spectrum overlapping and improve measurement accuracy almost one times.     

Production of binary amplitude gratings with arbitrary opening ratio and variable period

A simple double exposure technique is proposed for making binary amplitude gratings with preset opening ratio. Commercially available Ronchi type master ruling is imaged onto the photographic plate by a laser projection system. The controlled lateral displacement of the ruling or the photographic plate between two exposures results in the composite grating with the required opening ratio. A zoom-effect spherical beam projection system is suggested for producing binary gratings with continuously variable period.     

基于莫尔信号的精密位移测量与控制的研究

应用光衍射理论分析了一种纳米级位移分辨率的双级衍射光栅测量系统,建立了衍射莫尔信号与对应位移的数学模型,并通过计算机仿真对莫尔信号的位移特性进行了研究。在此基础上构建了一套精密位移测量与控制装置,取差动零次激光莫尔信号为控制信号,由微机控制实现高精度位移检测及全自动精密定位。实验结果表明,基于激光莫尔信号的精密检测与控制装置可获得得5nm的位移分辨率及±0.4μm的定位精度。     

一种改进型Stoilov算法相位测量轮廓术

提出了一种采用主动控制相移量的改进型Stoilov算法,按主动设定的相移量事先设计好五幅完全等相移正弦光栅图,由计算机编程控制数字投影仪依次投影该五幅光栅至待测物体表面,并对应采集五帧变形条纹,用所设定的相移量直接替代Stoilov算法中由变形条纹图解算的相移量,提高了相位提取和三维重构准确度.实验结果表明,平均绝对误差优于0.07,均方差优于0.07.     

Identifying a dot-matrix hologram by checking the intersecting angles of its gratings

Three features about the intersecting state of two gratings are used to identify dot-matrix holograms created by two-beam writers in this paper. The first feature is the intersection angle of the fringes of two gratings. The second feature is the ratio of the pitches of two lowest-order moiré-patterns formed by overlapping two gratings. The third feature is the length ratio of the two diagonal lines of a parallelogram constructed by two neighboring fringes of a first grating and two neighboring fringes of a second grating. All the three features are equivalent, i.e. they are all relative to the intersection angle of two gratings. Because the grating orientations of grating dots cannot be accurately reproduced for the orientation uncertainties of the components used by a two-beam writer, the intersection angles of the gratings of grating dots cannot be easily counterfeited. Therefore, the proposed methods are practical and feasible for the anti-counterfeiting applications of dot-matrix holograms.     

基于叠栅条纹的光刻对准理论分析及标定方法

在线光栅用于纳米光刻对准理论的基础上,为实现光栅方向的标定和掩模硅片对准,提出一种利用相位斜率消除角位移的新方法,并给出线光栅标记及其对准原理。在对准前,掩模对准标记和硅片对准标记存在角位移,重点讨论了此种情况下叠栅条纹的特性以及与光栅物理参数的关系,并给出了相应的计算公式。基于傅里叶频域分析法,对叠栅条纹频率成分与条纹的关系做了简要分析。利用提取叠栅条纹行列方向的一维相位,通过数据拟合,得出了相位斜率与角位移的内在关系,实现了条纹方向的标定。模拟实验结果表明,该方法简单可靠,可分辨的最小角位移低于0.02°。