基于双线空间像线宽不对称度的彗差测量技术

在高数值孔径、低工艺因子的光刻技术中,投影物镜彗差对光刻质量的影响变得越来越突出,因而需要一种快速、高精度的彗差原位测量技术。为此提出了一种新的基于双线空间像线宽不对称度的彗差测量技术,利用国际上公认的半导体行业光刻仿真软件PROLITH对该方法的测量精度进行了仿真分析。结果表明,与基于硅片曝光的彗差测量方法相比,基于空间像的彗差测量技术速度上的优势十分明显。其测量精度优于1.4 nm,较国际前沿的多照明设置空间像测量技术(TAMIS)提高30%以上,测量速度提高1/3左右。在ASML公司的PAS5500型步进扫描投影光刻机上,多次测量了投影物镜彗差,结果表明,该技术测量重复精度优于1.2 nm,能实现高精度的彗差原位测量。     

A novel method to measure coma aberration of projection system

A novel method to measure coma aberration by pattern displacements at different defocus positions is proposed in this paper. The effect of defocus on coma-induced pattern displacement is analyzed. The measuring principle of the method is described in detail. Using the simulation program PROLITH, the proportionality factors between pattern displacement and coma aberration at different defocus positions are calculated. It is proved that the method is simple to perform and the measurement accuracy of coma can increase approximately by 25% by this novel method.     

Trefoil aberration measurement of lithographic projection optics based on linewidth asymmetry of the aerial image

The degradation of critical dimension uniformity caused by trefoil aberration of lithographic projection optics is a serious problem in the production of dynamic random access memory devices. In the present paper, we propose a novel method for measuring the trefoil aberration of lithographic projection optics. The trefoil aberration can be extracted from the linewidth asymmetry of the aerial image of brick-wall patterns. The present method has an advantage of timesaving. The test mark used in the present method is easy and cheap to fabricate, and the model for aberration extraction is simple. The PROLITH simulation results show that the trefoil aberration can be measured with high accuracy.     

Shaft diameter measurement using a digital image

In this paper, a non-contact and high-precision method based on the processing of a digital image is presented to measure the diameter of a shaft. The method mainly involves three steps: first, the camera is calibrated by an improved approach, which only uses the feature points in the measurement area of the image to optimise the local camera model; second, with the help of the parameters of the model in the first step, a measurement method for determining the shaft diameter is proposed; finally, to embody the spatial attitude of the shaft accurately, the extrinsic parameters are re-calibrated by measuring a shaft whose diameter is known, and then the precision of measurement is improved by means of the new extrinsic parameters. The experimental data demonstrate that the proposed method exhibits high precision, with relative errors of approximately 0.005 mm.     

Velocity measurement for moving surfaces using spatial filtering method based on area image sensor

The idea of using spatial filtering method to measure velocity of vehicles for an inertial navigation system is put forward. Corresponding optical system, including a 532 nm solid-state laser as active illumination, is established. A 17.92 mm × 14.34 mm area charge coupled device (CCD) is employed both as detector and as spatial filter. The spatial filtering characteristics are theoretically analyzed using a power spectral density function. The spatial filtering operation of CCD is performed fully by software. Therefore, the parameters of the spatial filter, such as the size and the number of spatial period, are changeable. In addition, the CCD is arranged as two differential spatial filters without any other additional elements. Experiments are carried out to examine the feasibility of CCD as two differential spatial filters and the influence of the number of spatial period on the signal frequency. The results indicate that the more number of spatial period the more accurate measurements can be obtained, and show that the relation between signal frequency and velocity has good linearity. So this velocimeter is suitable to provide velocity information for a vehicle self-contained inertial navigation system.     

Evaluation of polychromatic image quality of a birefringent lens by means of optical transfer function

Polychromatic or white-light optical transfer function (OTF) is put forward as a criterion to evaluate the performance of a uniaxial birefringent lens sandwiched between two linear polarizers. The optic axis of the birefringent crystal is perpendicular to the lens axis. The results show that the same system may be adapted for both enhanced resolution and apodization just by rotating any of the polarizers included in the system even under broadband illumination. The proposed system may also be exploited for image processing applications under polychromatic input illumination.     

Strain and tilt measurement using multi-point diffraction strain sensor

A multi-point diffraction strain sensor (MDSS) was developed earlier by us for strain measurement with variable sensitivity and measurement range using a microlens array. The technique is now extended to measure both tilt and non-uniform strain with a sensitivity of 0.41 mε/pixel and 4.7 mrad/pixel. The validation was made through comparison of the strain measured using MDSS with that by a micro-Moiré interferometer incorporated with Gabor filtering method, while the tilt is compared with derivatives of the surface profile measured by a confocal microscope.     

Micro-displacement or bending measurement using a long-period fibre grating in a self-referenced fibre optic intensity sensor

The measurement of micro-displacement or bending using a long-period fibre grating (LPG) in a self-referenced fibre optic intensity sensor is presented. The sensing head is based on a LPG whose attenuation peak changes as a function of its micro-displacement or bending and the fibre optic intensity sensor is referenced in frequency. Two other LPGs were used as rejection filters, located at the output of the optical source to shorten its spectral width. The implemented experimental set-up is described and, the results are presented being considered the measurement range and the intrinsic resolution.     

Roughness measurement of metals using a modified binary speckle image and adaptive optics

This paper proposes an integrated roughness measurement system that is based on adaptive optics (AO) and binary analysis of speckle pattern images. The aim of this study was to demonstrate the necessity for AO compensation in regions containing both heat and fluid flow turbulences. A speckle image was obtained by projecting a laser beam onto the specimen surface, and the laser pattern image reflected from the surface was binarized to experimentally correlate the intensity with the surface roughness. In the absence of the AO correction scheme, induced turbulences can severely increase the residual rms error from 0.14 to 1.4 μm. After a real-time closed-loop AO correction, we can reduce the wavefront root mean square (rms) error to 0.12 μm, which not only compensates for the aberration error from induced disturbances but also improves the overall performance of the optical system. In addition, an AO system having different gains was investigated, and a threshold gain value was found to be able to steadily compensate for the wavefront errors in less than 2 s. Measurement results of five steel samples having roughness ranging from 0.2 to 3.125 μm (0.3λ and 5λ, where λ is the diode laser wavelength) demonstrate an excellent correlation between the intensity distribution of binary images and average roughness with a correlation coefficient of 0.9982. Furthermore, the proposed AO-assisted system is in good agreement with the stylus method and less than 9.73% error values can be consistently obtained.     

Profile measurement of a one-dimensional phase boundary sample using a single shot phase-step method

Phase shifting interferometry is a preferred technique for high-resolution phase profile measurement, but the difficulty in generating the requested shifted pattern has limited the use of the technique to low-noise environment and in case accurate calibration of the phase shifting device is available. In the present experiment, a sample having one-dimensional straight phase boundary is mounted in one arm of an interferometer. One single image of the fringe pattern is recorded, a simple image process is applied generating phase shifted patterns from the original image. Using the appropriate phase shift algorithms, a phase map of the sample is obtained which gives a quantitative measurement of the topographical structure with the resolution of the phase shift method but a single shot recorded pattern.     

用于头盔显示液晶像源的透镜薄膜设计与制备

LED已经成为头盔液晶显示的主流背光光源,为了提升LED主视角亮度,减小背光模块的体积,对双自由曲面透镜进行了扁平化设计,形成透镜薄膜,仿真结果表明光线透过透镜薄膜后,存在中心亮度升高、光斑缩小的问题.采用反馈优化方法修改了双自由曲面透镜设计时的能量分布,并重新设计了透镜薄膜,仿真结果表明优化后的光斑尺寸从2.3 mm...     

超大规模集成电路光学光刻技术的现状与展望

光学光刻是目前超大规模集成电路(VLSI)制备中主要的微米和亚微米的图形加工技术,这一技术将继续保持其主导地位成为90年代VLSI发展的关键。本文综述了近年来光学光刻工艺的发展,主要介绍了G线(436nm)、Ⅰ线(365nm)和准分子激光光刻的现状,并对实现高的光学光刻分辨率所必须解决的透镜设计、套准精度和像场面积等问题作了详细描述。最后展望了发展方向、     

Novel optical sensor for simultaneous measurement of liquid concentration and temperature

The paper describes a new optical sensor for simultaneous liquid concentration and temperature measurement. Temperature-dependent semiconductor absorption at the band edge is used as the principle of the temperature measurement, and the sensor exploits beam deviation caused by refraction due to the liquid concentration at the receiving end face of the optical device. The light intensity peak value and its deviation are detected by a charge-coupled device (CCD), and then the measured optical signal is reflected by a reflecting pyramid prism. The sensor probe is composed of an intrinsically pure GaAs single crystal, a reflecting pyramid prism, a partitioned water cell. Theoretical analysis and preliminary experimental results verify the feasibility of the proposed system.     

用H-S波前传感器测量穿过超声速流场的激光像差特性

 用Hartmann-Shack(H-S)波前传感器可以准确测量穿过超声速流场的激光波面及其变化过程,进一步计算可以获得光束质心漂移、远场分布等数据。给出了H-S方法测量穿过超声速流场激光波面的原理,采用模式法进行了波前重构,计算了在几种流场条件下的激光波面像差特性PV值,RMS值和Zernike像差系数、Strehl比和环围能量曲线等。结果表明,H-S法可以很好地反映流场建立、稳定和结束过程中Zernike像差的变化。比较无流场和给定参数的超声速流场,激光穿越后产生的最明显的像差变化为离焦和低阶像散的增大。在相同流场参数下,无模型时光束质量好于有模型时光束质量。     

A polarimetric glucose sensor using a liquid-crystal polarization modulator driven by a sinusoidal signal

Rather than using a conventional Faraday modulator, this study adopts a liquid-crystal based rotator to modulate the azimuth of the linear polarized light in a sinusoidal signal for the measurement of glucose concentrations. The tilt angle of the LC director would vary as a sinusoidal-like function; however the modulating frequency in the sensing system is the double of the driving signal. A new signal demodulation algorithm, therefore, is developed that enables the polarization rotation angle corresponding to the glucose concentration to be derived. The standard deviation in rotation angle level of 0.00551° has been obtained, with a 0.998773 correlation coefficient between the reference and the measured values. The proposed measurement method has a minimum resolvable concentration of 0.2 g/dl. Compared to its conventional counterparts, the developed polarimeter potentially has a simpler structure, fewer optical elements, and a cheaper modulator component.     

Multichannel image addition and subtraction using joint-transform correlator architecture

A simple technique for multichannel image addition and subtraction has been proposed using a basic joint-transform correlator architecture. Computer simulation and experimental results are provided. The geometry can also be modified to measure small relative displacement between objects, and to implement Hartley transform.     

Multi-focus image fusion using a bilateral gradient-based sharpness criterion

The aim of multi-focus image fusion is to combine multiple images with different focuses for enhancing the perception of a scene. The challenge is to how evaluate the local content (sharp) information of the input images. To tackle the above challenge, a new bilateral sharpness criterion is proposed to exploit both the strength and the phase coherence that are evaluated using the gradient information of the images. Then the proposed bilateral sharpness criterion is further exploited to perform weighted aggregation of multi-focus images. Extensive experimental results are provided to demonstrate that the proposed bilateral sharpness criterion outperforms conventional seven sharpness criterions.     

Optical performance simulation and optimization for CMOS image sensor pixels

Finite-difference time-domain (FDTD) method is used to perform three dimension simulations for the optical performance of 1.75 μm pitch pixels of CMOS image sensor. A three dimension pixel model for CMOS image sensor pixels is set up. Micro-lens optimization, dielectric stack height reduction can decrease the optical power loss. A SiN layer with proper thickness can reduce the reflection at the Si–SiO₂ interface. A high refractive index lightpipe is proposed to confine the light within the pixel. The simulation results show that the optical efficiency of the optimized 1.75 μm pixel compare to that before optimized is promoted by more than 10% and the cross-talk is reduced by 50%.     

基于紫外刻写相移光栅的温度应力同时测量传感器

传统光纤光栅传感器存在温度应力交叉敏感的问题,无法同时测量被测物体的温度应力变化情况.针对这种情况,提出一种新型的利用紫外光刻写相移光栅的方法,在刻写光栅前用电极放电的方法去除掉极小一段光纤的光敏性,使光纤原有的均匀周期分布状态被破坏,从而形成相移光栅,并对其进行理论分析.此种相移光栅的透射光谱存在2个明显的谐振峰,利...     

Edge linking and image segmentation by combining optical and digital methods

We present a hybrid method for segmentation of intensity images, which combines an optical contouring technique and digital algorithms for linking edge points or image segmentation. In a first stage, the digital image to be processed is displayed in a twisted-nematic liquid-crystal display (LCD), which is placed between a polarizer–analyzer pair at 45 deg (instead of 90 deg as occurs in standard LCDs). It is not difficult to demonstrate that the proposed setup produces a resultant image with very pronounced dark contours at middle intensity. After the optical preprocessing, two different digital algorithms are applied: an edge linking algorithm (modified chain code) and a simple thresholding technique for image segmentation. The proposed procedure works well with monochromatic and color images. The method could be useful as a robust technique for segmentation of large images in real-time, which presents potential applications in medical and biological imaging.