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Optical Engineering 47�5�, 053002 �May 2008�

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rojection optics design for tilted projection ofringe patterns

uan Shuonald Chunghe Chinese University of Hong Kongepartment of Mechanical and Automation

Engineeringong Kong, China-mail: [email protected]

heng Tani’an Jiatong Universitychool of Electronic and Information Engineeringhannxi, China

un Cheng*

he Chinese University of Hong Kongepartment of Mechanical and Automation

Engineeringong Kong, China

dmund Y. Lam, MEMBER SPIE

he University of Hong Kongepartment of Electrical and Electronic

Engineeringong Kong, China

enneth S. M. Fungan WangSM Assembly Automation Limitedwai Chung, N.T.ong Kong, China

Abstract. A challenge in the semiconductor industry is 3-D inspection ofthe miniaturized solder bumps grown on wafers for direct die-to-diebonding. An inspection mechanism proposed earlier requires the projec-tion of a binary fringe grating to the inspected surface from an inclinedangle. For high speed and accuracy of the mechanism, the projectionoptics has to meet these requirements: �1� it allows a tilt angle betweenthe inspected surface and the projector’s optical axis; �2� it has a highbandwidth to let high-spatial-frequency harmonics contained in the bi-nary grating pass through the lens and be projected onto the inspectedsurface properly; �3� it has a high modulation transfer function; �4� it hasa large field of view; and �5� it has an adequate depth of field thatmatches the depth range of the inspected surface. In this paper, wedescribe a projection optics design, consisting of a fringe grating andseveral pieces of spherical lens, that addresses the requirements. Toreduce the lens aberrations, the grating is laid out with an angle chosenspecifically to make the grating, the lens, and the average plane of theinspected surface intersect in the same line. Performance analysis andtolerance analysis are shown to demonstrate the feasibility of the design.© 2008 Society of Photo-Optical Instrumentation Engineers. �DOI: 10.1117/1.2931457�

Subject terms: machine vision; lens design; 3-D from structured light; modulationtransfer function; depth of field; field of view.

Paper 070738R received Sep. 24, 2007; revised manuscript received Feb. 10,2008; accepted for publication Mar. 9, 2008; published online May 30, 2008;corrected Jun. 3, 2008.

Introductionith the semiconductor industry advancing rapidly toward

maller, lighter, faster, and cheaper products, area arrayackages, including ball grid arrays, chip-scale packages,ip-chip packaging, wafer bumping, and wafer-level pack-ging �WLP�, are quickly becoming the focus of IC pack-ging technology. They could help improve device perfor-ance and manufacturability, and ultimately reduce cost.However, the shrunk dimension of the devices also leads

o more stringent requirement on process control and qual-ty assurance. A particular challenge is the development ofision techniques for inspecting the 3-D surface of waferumps accurately and efficiently. There have been a fewoncontact optical shape measurement methods proposedn the literature: laser triangulation,1–3 confocalicroscopy,4,5 sinusoidal pattern projection,6 and moiré

nterferometry.7,8 However, these methods suffer from ei-her low speed or high sensitivity to noise. In an earlierork we proposed a new mechanism for reconstructing wa-

Current affiliation: Shenzhen Institute of Advanced Integration Technol-gy, Chinese Academy of Sciences/The Chinese University of Hongong.

091-3286/2008/$25.00 © 2008 SPIE

ptical Engineering 053002-

fer bump surfaces in 3-D.9,10 As shown in Fig. 1, thegrating is projected onto the inspected surface at an inci-dent angle of 30 deg. The mechanism is based on project-ing a binary pattern to the surface and capturing image ofthe illuminated scene. By shifting the binary pattern in

Fig. 1 3-D wafer measurement system.

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Shu et al.: Projection optics design for tilted projection…

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pace and every time taking a separate image of the illumi-ated surface, each position on the illuminated surface wille assigned a binary code in the sequence of images taken.ith a suitable design of the binary pattern, the binary code

an be made unique for each bump surface position. Withuch binary codes, correspondences between image posi-ions and positions of the projected pattern can be readilystablished. 3-D information about the bump surface canhen be obtained over these coded points via triangulation.

The design of the projection lens, which determines theuality of the projected fringes on the inspected surface, ismportant for the proposed inspection system. To recon-truct 3-D surfaces with high speed and accuracy, there arehe following requirements for the projection lens system:1� it allows a tilt angle of about 60 deg between the in-pected surface and the projector’s optical axis; �2� it has aarge bandwidth to let high-spatial-frequency harmonicsontained in the binary grating pass through and be pro-ected onto the inspected surface properly; �3� it has a large

odulation transfer function �MTF�; �4� it has a large fieldf view �FOV� of about 10�10 mm over the inspectedurface, to speed up the reconstruction process; �5� it has aarge depth of field �DOF� that corresponds to the height ofhe inspected surface. The above requirements lead to greathallenges in the projection lens design. This paper ad-resses the design of such a projection system.

The organization of the paper is as follows. Section 2utlines the design issues, including the MTF requirementf the designed lens, the key factors for correcting lensberration, and the methodology of improving the depth ofeld of the lens. Two designed lens systems that meet theequirements are described in Sec. 3. Concluding remarksre presented in Sec. 4.

Design Issueshe grating pattern projection system is to project a patternnto the microsurface in such a way that the pattern, oneflection from the surface and imaging by the camera, willetain the fine details to a specified level. The main con-erns in the design of the system are the defocus �modula-ion reduction� and image distortion �pattern variation� inhe propagation of the light. The distortion will cause anffset of both the grating position and the pitch variation,hich generally affect the 3-D �height� measurement; also,

he modulation reduction will reduce the SNR and in turnhe accuracy of the projected pattern edge detection.

Fig. 2 Luminan


2.1 Image Modulation Requirement of theProjection System

A binary pattern �stripe grating� is a repeating sequence oflight and dark bars, with one pair of adjacent light and darkbars making up each cycle. These cycles repeat in a grating.These square gratings in the captured image data are sup-posed to be reducible to a set of sharp edges like the barsshown in Fig. 2.

A binary pattern f�x� of period 2L can be expressed by aFourier series:

f�x� =4

��

n=1,3,5,. . .

�1

nsin�n�x

L� . �1�

It consists of more high-frequency components than a sinu-soidal grating, and the amplitudes of the components getsmaller as the frequencies go up. When the binary pattern isprojected onto the inspected surface through a set of pro-jection lenses, the high-order harmonics of the pattern willbe diminished because of the lenses’ limited bandwidth.Therefore, crisp fringes as shown in Fig. 2, when projectedonto the inspected surface, will not remain perfectly blackor white, but will appear as gray-level fringes. In otherwords, the boundaries of the binary stripes will appearblurred in the captured image data. When a binary gratingwith spatial frequency � is projected on the reference plane

binary grating.

Fig. 3 Intensity distribution of edges with different MTF values.

ce of a

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hrough the projection lens, the modulation transfer func-ion �MTF� of the projection lens is defined as

TF =Mi��Mo��

, �2�

here Mi is the modulation of the projected fringes and Mos the modulation of the grating. The MTF is a function ofhe spatial frequency �, which decreases rapidly with in-reasing �.

The sharper is an edge, the higher frequency compo-ents it contains. Figure 3 illustrates a set of intensity pro-les around the edge region, varying from smooth to sharp.he smooth edges do not contain enough high-frequencyarmonics to present a rapid transition. Only with moreigher-frequency harmonics retained could sharper edgese obtained. To sharpen the edge between black and whitetripes in the projection, more harmonics of the proper fre-uency and amplitude should pass through the projectionens.11,12

Experiments show that if in the image data we are toapture fringes with sharp enough edges on the inspectedurface, we need to design a projection lens with a highTF value for the fifth harmonic of the grating’s spatial

requency. As our system requires a binary grating with 10ine pairs per millimeter �1p/mm�, we need to design a lensith good MTF performance at 50-lp /mm spatial fre-uency.

.2 Aberration Corrections of the Cross-Axis Opticsarious kinds of aberrations occur when light passes

hrough the portion of the lens that is distant from the lensenter. They include spherical aberration, coma aberration,hromatic aberration, and so on.13 Symmetric doublets caneduce the spherical aberration greatly. More completeoma aberration correction can be achieved by using aombination of lenses that are symmetric about a central

Fig. 4 Optical axis inclination


stop, such as double Gauss lenses. One way to minimizethe chromatic aberration is to use glasses of different dis-persions in a doublet or in other combinations. In this work,we use a combination of different lenses to compensate thelens aberration.

Cross-axis layout of the CCD camera and the gratingprojector require that the image plane �i.e, the referenceplane shown in Fig. 4, which is the average plane of theinspected surface� be not perpendicular but tilted with re-spect to the optical axis of the projector. In other words, thebinary grating is projected onto the inspected surface at anoblique angle �. Large � can improve the 3-D reconstruc-tion precision of the inspected wafer. However, it willgreatly increase the lens aberration and reduce the MTF.

The first problem arising from this optical layout is thatthe lateral magnifications for the upper and lower edges ofthe image plane are different. This so-called keystone dis-tortion is caused by the fringe pattern projection directionnot being perpendicular to the image plane14,15 of the cam-era. The keystone distortion is not symmetric with respectto the optical axis; thus we cannot use the conventional

of the grating projection unit.

Fig. 5 Scheimpflug optics layout of the tilted grating and imageplane.

setup

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pherical lens combination for correcting it at all positionsn the image plane. The second problem is that the focusingcuity of the image changes linearly from the lower to thepper edge of the image plane. The image can at any par-icular setting be in sharp focus only over a horizontal stripf it. The solution in our design is to use the Scheimpflugptical system to eliminate both the keystone distortion andhe linear defocusing effect. It differs from the conventionalechniques in that the object plane, lens plane, and imagelane are not parallel to each other, but intersect in a com-on straight line. Furthermore, the lines where the grating

nd image planes intersect with the corresponding principallanes must have the same height, as shown in Fig. 5. Wean see that the required tilting of the grating plane toliminate the keystone distortion is in the opposite sense tohat required for focusing the image over the entire imagelane.15 The chief advantage of the Scheimpflug geometrys that a large depth of focus can be achieved.16

Let R1 be an arbitrary vector in the grating plane in-lined at angle P to the axis of the input lens, and R2 be therojected image of R1 in the image plane from an inclina-ion angle Q. Let m be the magnification of the projectionens. Then R1 can be decomposed into three orthogonalomponents x1, y1, and z1 �shown in Fig. 5�. Since thenclination of the grating plane is a constant angle P, theollowing relationship will always be satisfied:

anP = z1/x1,

anQ = z2/x2. �3�

The components of the image R2 of R1 will be similarlyesigned so that x2, y2, z2 are related to the grating compo-ents by

2 = − mx1,

2 = − my1,

Fig. 6 Symmetrical field of view in the 10�10-mm image plane.

Fig. 7 3-D layout model of the projection lens.


z2 = m2z1, �4�

where m2 is the familiar longitudinal magnification.The relation between the tilt angle P of the grating pat-

tern plane and the tilt angle Q of the image plane can beexpressed as

tanQ = − m tanP . �5�

Using the method of tilting the grating plane, the off-axis keystone distortion can be corrected properly.

Table 1 Specifications of the designed lens system with larger DOF.

Surfaceno.

Radius of curvature�mm�

Thickness�mm� Material

Object � 14.00 Air

1 � 3.00 BK7

2 24.53 14.15 Air

3 82.92 3.00 SF5

4 21.38 7.89 SK11

5 −28.75 7.60 Air

6 26.68 11.49 SF5

7 21.84 20.09 Air

8 83.79 2.00 SF5

9 28.12 5.00 BK7

10 −35.92 6.89 Air

11 � 100.00 BK7

12 � 63.39 Air

Image �

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

Fig. 8 Spot diagrams of three fields of view of the two projectionlenses.

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.3 Improving the Depth of Field for Bumped BallImaging

hen a lens focuses on an object at a distance, only thearts of the object that are exactly at that depth are in focus.ther parts are out of focus. The zone of acceptable sharp-ess is referred to as the depth of field �DOF�. Since theverage height of the bump is from 80 to 400 �m, theptics should have a DOF of about 400 �m. Increasing the

Table 2 Parameters of t

DOFSurface

no.

DistanceOI

�mm�

Focallength�mm�

Small 14 210.48 39.72

Large 14 244.52 40.88

� � �

Fig. 9 MTF of t


DOF of the projection lens increases the sharpness of thedeformed pattern image. The DOF can be calculated as

�L1 =F�L2

f2 + F�L,

designed lens systems.

Aperature�mm� Magnification

MTF@50

lp/mm

9.05 −2.134 0.52

8.00 −2.62 0.44

� � �

ll-DOF design.

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L2 =F�L

f2 − F�L,

L = �L1 + �L2 =2f2F�L2

f4 − F�2L2 , �6�

here � is the diameter of the acceptable circle of confu-ion, f is the focal length of the lens, F is the aperture �or Ftop�, L is the focused subject distance �this is what is setn the lens focus scale�, �L1 and �L2 are the near and faristance values of the DOF, respectively, and �L is thehole DOF of the optics. From Eq. �6�, we know that theOF can be increased by reducing the lens’s aperture.

Projection System Design and PerformanceAnalysis

he projection lens is required to properly project the bi-ary grating of spatial frequency 10 lp /mm to the inspectedurface with FOV of 10�10 mm. In order to capture theeformed fringes with sharp edges, a high modulation athe fifth harmonic of the base frequency is needed. TheEMAX software17 is used in this optics design. The com-rehensive software tool for optics design integrates all theeatures required to conceptualize, design, optimize, ana-yze, tolerance-insert, and document virtually any opticalystem.

.1 Designed Projection Systemonsider a FOV 10�10 mm. Five symmetrical positions,s shown in Fig. 6, are used for performance analysis. Theurpose of the design is to optimize all parameters of theptics: radii, thickness, glasses, conics, aspheric coeffi-ients, and so on. The layout of the designed projectionptics, whose aperture is 9.05 mm, is shown in Fig. 7.

In order to improve the DOF of the projection lens, theperture of the first designed optics was reduced to 8 mm.he modified design with a larger DOF is shown in Fig. 7.he components’ parameters for the modified design arehown in Table 1.

The parameters of the two designed systems are shownn Table 2, where the distance OI is the total length fromhe grating to the image of the lens. From Table 2, we canee that as the aperture is reduced from 9.05 to 8.00 mm,he MTF is also reduced a little, from 0.52 to 0.44.

As for the designed system with small DOF, the tiltngle of the image plane is Q=30 deg, the tilt angle of therating is P1=15.04 deg, and the optical paraxial magnifi-ation m1 is −2.134. From Eq. �5�, it can be determined thathe relation between the tilted image and grating plane isanQ / tanP1�−m1.

For the designed system with the larger DOF, the tiltngle of the image plane is also Q=30 deg, the tilt angle ofhe grating pattern is P2=12.35 deg, and the opticalaraxial magnification m2 is −2.62. The relation betweenhe tilted image and grating plane of this modified design isanQ / tanP2�−m2.

.2 Performance Analysisn ideal lens will focus an input parallel beam to a point

focal point�, which should be infinitesimally tiny. How-ver, because of lens aberrations and diffraction, the focal


spot of a real lens has a finite size. All singlet lenses have asignificant amount of aberration. Figure 8 shows a so-calledspot diagram in the case that the grating plane and theimage plane are placed at right angles to the optical axis ofprojection. In general, elimination of the keystone distor-tion can have the effect that the average image spot size atthe edge of the field is increased.

To describe the lens’s ability to transfer contrast at a

Fig. 10 MTF of the large-DOF design.

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articular resolution level from the grating to the image, theTF curves at three image positions �0,0�, �5,5�, and

−5,−5� are shown in Fig. 9 and Fig. 10. In each graph,here are two curves, one for the tangential MTF and thether for the sagittal MTF. The reason for the differenceetween the two plots is that the point spread function be-omes asymmetric off axis, which means the resolution inhe two directions is also different.

A graph of the encircled fraction of the energy plottedgainst the radius of the aperture is called the radial energyistribution curve. The curve �shown in Fig. 11� indicateshe fraction E of the total energy in an image pattern thatalls in a circle of radius R.

If the acceptable sharpness in imaging target object ispecified by a MTF at 50 lp /mm of 0.3, the DOF can bemproved from 380 to 470 �m when the aperture is re-uced from 9 to 8 mm, as shown in Fig. 12. Such a design

Fig. 11 Encircled-energy

Fig. 12 Depths of field of the two projection lenses at �0, 0�.


with higher DOF can cover the average height of the in-spected bumps, which is from 80 to 400 �m. The MTFparameters are reduced only a little, from 0.48 to 0.43 atposition �0,0� in the image plane.

3.3 Tolerance AnalysisThrough the MTF curve shows what a lens is capable oftheoretically under the optical prescription, it does not in-dicate the actual performance of the lens after manufactur-ing. Manufacturing always introduces some performanceloss in the design, due to tolerances. For this reason, toler-ance testing enables characterization of the actual perfor-mance of both the designed lens and the manufactured lens.Table 3 and Table 4 give the tolerance data and the simu-lated MTF parameters after considering the tolerance of themanufacturing, as well as the performance requirements ofthe optical system.

Note that theoretically with the use of more componentlenses the performance of a lens system can be further im-

Table 3 Typical optical fabrication tolerance.13

GradeDiameter

�mm�Thickness

�mm� Radius

Lineardimension

�mm� Angles

Low cost ±0.2 ±0.5 Gauge ±0.5 Degrees

Commercial ±0.07 ±0.25 10 fr. ±0.25 15arcmin

Precision ±0.02 ±0.1 5 fr. ±0.1 �5to10�arcmin

Extraprecise

±0.01 ±0.05 Asreqd.

Asreqd.

Arcseconds

of the large-DOF design.
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Fig. 13 3-D reconstruction of a small solder surface with the use of the grating projection system.

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roved. However, the use of more lenses could also bringbout larger tolerances in the manufacturing process andffect the actual optical performance. The manufacturingost will also increase.

.4 Real Image Experimentsxperiments have been conducted to inspect the microsol-er epoxy on an IC packaging device surface, for which theroposed projection system is a key component of the re-onstruction system. In the result presented in Fig. 13, theeight distribution of a very small solder surface �the wholebject surface was no bigger than 12 mm�12 mm600 �m� was inspected to show the 3-D profile measure-ent capability of the system for small-form parts. The

econstruction system, detailed in Refs. 9 and 10, uses theroposed projection system to project the fringe gratingrst to a reference plane and then to the target surface. The

mage data taken separately for the two surfaces are thenompared through an algorithm, and 3-D measurements ofhe target surface can be obtained with reference to theeference plane. Figure 13�a� shows an image of the refer-nce plane under the pattern projection. It was part of aalibration step. Figure 13�b� shows the image of the targetbject under pattern projection. Figure 13�c� shows the re-onstructed height distribution of the object. Figure 13�d�hows a 2-D plot indicating a cross section of the recon-tructed solder epoxy profile height from image position50, 108� to �280, 108� �the red line� in Fig. 13�b�.

Thorough evaluation experiments against ground truthave been conducted. The ground truth was measured by aachine of high precision and accuracy—the ZYGOachine—and the solder epoxy profile was detected usingphase-shifting interferometer with 0.1-�m height reso-

ution. The comparison shows that in the direction of theeight measurement a mean squared error of no more than.43 �m was achieved by the 3-D reconstruction system,nd that confirms the validity of the proposed gratingrojection system design in achieving quality 3D recon-truction.

Conclusiono realize an optical system for semiconductor surface in-pection, a design of a projection lens system with the fol-owing requirements is needed: �1� it allows a tilt betweenhe inspected surface and the projector’s optical axis; �2� itas large bandwidth; �3� it has large MTF; �4� it has largeOV; and �5� it has large DOF. We have described how theesign challenge can be met using a combination of lenses

able 4 Tolerance tests �Monte Carlo, 20 repetitions� on the twoesigned lenses.

MTF at 50 lp/mm

OF 90% 50% 10%

mall 0.36 0.43 0.48

arge 0.33 0.39 0.42


and a method of correcting keystone aberration. The de-signed projection lens system can project a binary gratingonto the inspected surface with sharp contrast between thelight and dark fringes. Theoretical analysis demonstratesthe feasibility of the design.

Acknowledgment

The work described in this paper was substantially sup-ported by a grant from the Innovation and TechnologyCommission of Hong Kong Special Administrative Region,China, under an Innovation and Technology Fund withProject Code UIM/111.

References

1. H. Stern, “Laser based 3-d surface mapping for manufacturing diag-nostics and reverse engineering,” in Proc. IEEE Conf. on Aerospaceand Electronics, pp. 1205–1212 �1992�.

2. S. Wang, B. Zhuang, and W. Zhang, “New principle of optical dis-placement measurement based on light scattering from rough sur-face,” in Three-Dimensional and Laser-Based Systems for Metrologyand Inspection II, K. Harding and D. Svetkoff, Eds., Proc. SPIE2909, 37–42 �1997�.

3. C. Tay, S. Wang, C. Quan, B. Lee, and K. Chan, “Measurement of amicro-solderball height using a laser projection method,” Opt. Com-mun. 234, 77–86 �2004�.

4. M. Ishihara and H. Sasaki, “High-speed 3d shape measurement usinga nonscanning multiple-beam confocal imaging system,” in LaserInterferometry IX: Techniques and Analysis, M. Kujawinska, G. M.Brown, and M. Takeda, Eds., Proc. SPIE 3478, 68–75 �1998�.

5. A. Rao, N. Ramesh, F. Wu, J. Mandeville, and P. Kerstens, “Algo-rithms for a fast confocal optical inspection system,” in Proc. IEEEWorkshop on Applications of Computer Vision, pp. 298–305 �1992�.

6. V. Srinivasan, H. Liu, and M. Halioua, “Automated phase-measuringprofilometry of 3-d diffuse objects,” Appl. Opt. 23, 3105–3108�1984�.

7. C. J. Tay, S. H. Wang, and C. Quan, “Height measurement of micro-chip connecting pins by use of stereovision,” Opt. Eng. 43, 963–970�2004�.

8. S. Kim, Y. Choi, and J. Oh, “Three-dimensional profile measurementof fine object by phase-shifting moiré interferometry,” in Three-Dimensional and Laser-Based Systems for Metrology and InspectionII, K. Harding and D. Svetkoff, Eds., Proc. SPIE 2909, 28–36 �1997�.

9. J. Cheng, R. Chung, E. Lam, K. Fung, F. Wang, and W. Leung,“Three-dimensional reconstruction of wafer solder bumps using bi-nary pattern projection,” in Machine Vision Applications in IndustrialInspection XIII, J. R. Price and F. Meriaudeau, Eds., Proc. SPIE5679, 44–52 �2005�.

10. J. Cheng, R. Chung, E. Lam, K. Fung, F. Wang, and W. Leung,“Structured-light based sensing using a single fixed fringe grating:fringe boundary detection and 3d reconstruction,” IEEE Trans. Elec-tron. Packag. Manuf. 31�1�, 19–31 �2008�.

11. J. Goodman, Introduction to Fourier Optics, McGraw-Hill, New York�1996�.

12. M. Born and B. Wolf, Principles of Optics, Pergamon Press, Oxford�1987�.

13. J. S. Warren, Modern Optical Engineering: The Design of OpticalSystems, McGraw-Hill �1990�.

14. B. Li and L. Sezan, “Automatic keystone correction for smart projec-tors with embedded camera,” in Proc. IEEE Int. Conf. on ImageProcessing, Vol. 4, pp. 2829–2832 �2004�.

15. V. M. Durán-Ramírez and D. Malacara-Doblado, “Keystone aberra-tion correction in overhead projectors,” Appl. Opt. 43, 4123–4126�2004�.

16. A. K. Prasad and K. Jensen, “Scheimpflug stereocamera for particleimage velocimetry in liquid flows,” Appl. Opt. 34, 7092–7099 �1995�.

17. ZEMAX Development Corp., http://zemax.com/zemax/ �2004�.

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http://dx.doi.org/10.1016/j.optcom.2004.02.014

http://dx.doi.org/10.1016/j.optcom.2004.02.014

http://dx.doi.org/10.1117/1.1668284

http://dx.doi.org/10.1364/AO.43.004123

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Yuan Shu received his PhD degree in com-munication and information systems fromthe Institute of Signal Processing of Xi’anJiaotong University, China, in December2005. Before that, he received his BS andMS degrees in applied physics and optics,both from Xi’an Jiaotong University, 1998and 2001, respectively. He was a researchassistant with the Computer Vision Labora-tory �CVL�, Department of Mechanical andAutomation Engineering, the Chinese Uni-

ersity of Hong Kong �CUHK�, between November 2004 and April005. Now, he is a computer vision software engineer in a globalemiconductor equipment company. His research interests are in-D reconstruction, high-precision pattern alignment, microdefect in-pection, and machine vision.

Ronald Chung received his BSEE from theUniversity of Hong Kong, Hong Kong, andhis PhD in computer engineering from Uni-versity of Southern California, Los Angeles.He is currently with the Chinese Universityof Hong Kong, Hong Kong, as director ofthe Computer Vision Laboratory and profes-sor in the Department of Mechanical andAutomation Engineering. His research inter-ests include computer vision and robotics.He is a senior member of the IEEE, a char-

ered engineer of the Engineering Council of the UK, and a memberf Mensa. He was the chairman of the IEEE Hong Kong Sectionoint Chapter on Robotics & Automation Society and the Controlystems Society in the years 2001 to 2003.

Zheng Tan received the BA degree from theDepartment of Electronic Engineering ofXi’an Jiaotong University in 1960. Since1984, he has been with the Institute of Sig-nal Processing of Xi’an Jiaotong University,China. Now he is a professor and a PhDstudent supervisor. His research interestsare in stereo vision, digital entertainment,and virtual reality. He has published morethan 60 papers in national and internationaljournals and at international conferences.

Jun Cheng received bachelor of engineer-ing, bachelor of finance, and master of en-gineering degrees from the University ofScience & Technology of China in 1999 and2002. His PhD degree was awarded at theChinese University of Hong Kong in 2006.Currently he is with Shenzhen Institute ofAdvanced Integration Technology, ChineseAcademy of Sciences/The Chinese Univer-sity of Hong Kong, as a research associatefellow and director of the Laboratory for

emiconductor Equipment. His research interests include computerision, robotics, machine intelligence, and control.

ptical Engineering 053002-1

Edmund Y. Lam received the BS degree in1995, the MS degree in 1996, and the PhDdegree in 2000, all in electrical engineering,from Stanford University. At Stanford, hewas a member of the Information SystemsLaboratory, conducting research for theStanford Programmable Digital Cameraproject. His focus was on developing imagerestoration algorithms for digital photogra-phy. Outside Stanford, he also consulted forindustry in the areas of digital camera sys-

tems design and algorithms development. Before returning to aca-demia, he worked in the Reticle and Photomask Inspection Division�RAPID� of KLA-Tencor Corporation in San Jose as a senior engi-neer. His responsibility was to improve on the core die-to-die anddie-to-database inspection algorithms, especially for phase-shiftmasks. Dr. Lam is currently an assistant professor in the Depart-ment of Electrical and Electronic Engineering at the University ofHong Kong. He is a member of the IEEE and SPIE.

Kenneth S. M. Fung is the technical man-ager in the Research and Development De-partment at ASM Assembly Automation Lim-ited. After receiving the PhD degree in 1999from the Department of Electrical and Elec-tronic Engineering at the University of HongKong, he joined ASM Assembly AutomationLimited as a senior engineer. He developeda subpixel-accuracy, high-speed, and ro-bust computer vision alignment algorithmthat was applied in all ASM products and

boosted the capability and vision technology level of the company’ssemiconductor packaging machines. Currently, he leads a team ofresearch engineers responsible for the projects in machine visioninspection and algorithm development. He also provides technicalsupervision for a team of vision application engineers who are re-sponsible for the projects in developing machine vision applicationson ASM products. Kenneth’s research interests are computer vision,pattern recognition, digital image processing, and artificial neuralnetworks.

Fan Wang finished his undergraduate studyin Tianjin University, China, in 1985, and ob-tained a master in physics degree fromSouth China University of Technology,China, in 1988. He subsequently went backto Tianjin University, China, and obtainedhis PhD there in 1991. He has published onoptical association memory and optical in-formation processing. His recent interestsinclude optical projector and 3-D displaytechnologies.

May 2008/Vol. 47�5�0

projection optics design for tilted projection of fringe...

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