Chenggen Quan

National University of Singapore, Tumasik, Singapore

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Publications (188)215.63 Total impact

  • C.G. Quan · W. Chen · C.J. Tay
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    ABSTRACT: This paper discusses several phase-retrieval techniques commonly used in fringe-projection profilometry (FPP). The FPP has become a suitable and powerful method for the measurement of object surface shape, and some algorithms have been proposed to extract phase maps, such as Fourier transform profilometry (FTP). In this paper, FTP, phase-shifting and continuous wavelet transform (CWT) are briefly described and discussed. In addition, two-dimensional short-time Fourier transform (STFT) is also presented to extract wrapped phase maps. Simulations and experimental results are presented to show the performance of these phase-retrieval techniques in FPP.
    No preview · Article · Feb 2010 · Optics and Lasers in Engineering
  • C. Quan · H. Niu · C.J. Tay
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    ABSTRACT: A modified algorithm of windowed Fourier transform (WFT) for phase retrieval from electronic speckle-shearing fringe patterns with carriers is proposed. The algorithm is based on the introduction of a fast Fourier transform (FFT) in WFT to reduce computation time for fringe demodulation. Since boundary effects in FFT will influence the accuracy of phase retrieval, the Gerchberg method is employed to extrapolate the fringe pattern at the boundaries to reduce boundary effects. A theoretical analysis of the algorithm is presented. Both simulated and experimental results show that the proposed method has reduced the computation time significantly compared with the convolution method of WFT without sacrificing measurement accuracy.
    No preview · Article · Feb 2010 · Optics & Laser Technology
  • C. J. Tay · C. Quan · M. L. Ling · Q. Lin · G. S. Chua
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    ABSTRACT: In this article, the effect of a defective mask on 193 nm immersion lithography with a 6% attenuated phase-shifting mask is investigated. Two types of defect are studied: process related defect and haze defect. Several factors including defect location, size, transmission, phase, and illumination settings are considered. Exposure using a standard 45 nm SRAM cell shows that the printability of a defect on a mask depends on the pattern density and defect size and it is also shown that the impact of a defect on a polysilicon gate layer is worse than that on an active layer. A defect that is adjacent to a main feature causes more critical dimension (CD) variation than that between two main features. Simulation using a through pitch line and space pattern is used to investigate the impact of a haze defect. A change in transmission results in an increase in the CD variation in the main feature but not the critical defect size. However, a larger phase difference between the defect and background would increase the CD variation and reduces the critical defect size. Illumination with a low partial coherence setting increases the CD variation caused by defects.
    No preview · Article · Jan 2010 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
  • Cho Jui Tay · Chenggen Quan · Mingzhou Li
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    ABSTRACT: In this work, a white light interferometry technique has been developed for measuring the thickness of a multi-layer structure. Essentially, the method utilizes a white light source, which illuminates a test object mounted on a translation stage, using a modified Michelson interferometer configuration. Images of the object are recorded at certain prescribed vertical movements of the translation stage via a PZT. Tests are conducted on a dual layer semi-conductor wafer and a micro-gear. The results obtained show that the thickness and profile of a micro-gear fabricated from a polymer can be determined with good accuracy.
    No preview · Article · Jan 2010
  • Wen Chen · Chenggen Quan · Cho Jui Tay
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    ABSTRACT: In this paper, we propose a method for optical image encryption based on fractional Fourier transform (FRFT) and Arnold transform (ART) in phase-shifting digital holography. An input image is first divided into eight bit planes, and each bit plane is encrypted based on double random-phase masks and FRFT. Complex amplitude for the object is retrieved by phase-shifting digital holography in the hologram plane. The real and imaginary parts of the retrieved complex amplitudes for the 0th-7th bit planes are further encrypted using ART algorithm. Numerical results are shown to demonstrate the feasibility and effectiveness of the proposed technique. The sensitivity of security parameters, such as function orders in FRFT and iteration number in ART method, is also analyzed.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    No preview · Article · Dec 2009 · Proceedings of SPIE - The International Society for Optical Engineering
  • H. Niu · C. Quan · C. J. Tay
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    ABSTRACT: Time-frequency analysis is widely applied to the optical measurement for phase retrieval from fringe patterns. Windowed Fourier transform (WFT) is one of the time-frequency analysis methods and has recently received extensive study on phase retrieval from fringe patterns generated by the optical interferometry or structured light illumination. WFT has been applied for shape and deformation measurement in dynamic nondestructive testing. However, the computation time of WFT is longer than that of conventional Fourier transform method for fringe demodulation. This has restricted the WFT in the application for dynamic measurement. Therefore, a modified WFT is introduced to reduce the computation time. In this approach, the fast Fourier transform is implemented in the WFT algorithm to improve the computational efficiency and border effect of the proposed method for fringe analysis is discussed. The phase retrieval of the proposed method is simulated and the simulation results are compared with conventional Fourier transform method and convolution method of WFT in terms of noise reduction. The experimental work on shape and deformation measurement is conducted to verify the effectiveness and validity of the proposed method.
    No preview · Article · Dec 2009 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: A novel concept of contact holes patterning for 193 nm immersion lithography is demonstrated in this study. Conventional contact holes patterning involve targeting a square printed feature on the wafer and applying optical proximity correction (OPC) such as corner serifs addition and dimensional biasing. As dimension of contact holes reduces, the resolution enhancement provided by conventional OPC methods has become limited. This is because at smaller dimension, more light is diffracted towards higher order and is not captured in the pupil plane. As a result, the corners of the printed features are rounded and features appear circular as dimension reduces. Hence, the efforts made to generate OPC assist features using a square target are inefficient. In this paper, the patterning of contact hole using circular target is demonstrated. The imaging performance of isolated and regular contact holes array is reported. Comparison with conventional approach is made. The effects of the proposed method on critical dimension (CD), depth of focus (DOF), and image contrast is investigated.
    No preview · Article · Dec 2009 · Proceedings of SPIE - The International Society for Optical Engineering
  • B. Bhaduri · C. J. Tay · C. Quan
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    ABSTRACT: Digital speckle pattern interferometry (DSPI) is a tool for making qualitative as well as quantitative measurements of deformation of objects. Temporal and spatial phase shifting techniques have been introduced in DSPI for extracting quantitative deformation data from the system. Temporal phase-shifting technique requires at least three phase shifted intensity patterns for phase measurement. On the other hand, spatial phase shifting technique though require single frame before and after the object deformation, gives low spatial resolution result. In this paper we propose a temporal phase shifting technique that uses only two phase shifted speckle patterns before and after the object deformation by suppressing the dc-term from the intensity pattern either by an averaging technique in spatial domain or low-pass filter operation in the frequency domain. Both the simulation and experimental results are presented to validate the effectiveness of the proposed technique.
    No preview · Article · Dec 2009 · Proceedings of SPIE - The International Society for Optical Engineering
  • H. Niu · C. Quan · C.J. Tay
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    ABSTRACT: A novel two-dimensional (2D) Gabor continuous wavelet transform (CWT) for phase retrieval and fringe filtering of speckle fringe patterns with spatial carriers is proposed. Theoretical analysis of 2D Gabor CWT is presented and results are compared with advanced fan 2D CWT using both the computer simulated and experimental speckle fringe patterns. It is shown that noise reduction by 2D Gabor CWT demonstrates better results than that of the advanced fan 2D CWT. Two-dimensional Gabor CWT is also compared with 2D Fourier transform and results show that 2D Gabor CWT algorithm has better noise immunity.
    No preview · Article · Dec 2009 · Optics and Lasers in Engineering
  • Wen Chen · Chenggen Quan · Cho Jui Tay
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    ABSTRACT: In this paper, we propose a method for optical image encryption based on fractional Fourier transform (FRFT) and Arnold transform (ART) in phase-shifting digital holography. An input image is first divided into eight bit planes, and each bit plane is encrypted based on double random-phase masks and FRFT. Complex amplitude for the object is retrieved by phase-shifting digital holography in the hologram plane. The real and imaginary parts of the retrieved complex amplitudes for the 0th-7th bit planes are further encrypted using ART algorithm. Numerical results are shown to demonstrate the feasibility and effectiveness of the proposed technique. The sensitivity of security parameters, such as function orders in FRFT and iteration number in ART method, is also analyzed.
    No preview · Article · Dec 2009 · Proceedings of SPIE - The International Society for Optical Engineering
  • Wen Chen · Chenggen Quan · Cho Jui Tay
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    ABSTRACT: We propose a method to extend the depth of focus in a particle field measurement using a single-shot digital hologram. A focal plane is obtained for each pixel based on an entropy method, and a depth map is subsequently extracted. A synthesized extended focused image is determined correspondingly using the extracted depth map. In addition, a wavelet modulus maxima algorithm and Canny algorithm are further employed to detect the edges of each particle, and the sizes and a three-dimensional localization of the particles are also estimated. Preliminary results are presented to show the feasibility and effectiveness of the proposed technique.
    No preview · Article · Nov 2009 · Applied Physics Letters
  • W. Chen · C. Quan · C.J. Tay
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    ABSTRACT: In this paper, we propose a novel method to encrypt a color image based on Arnold transform (ART) and interference method. A color image is decomposed into three independent channels, i.e., red, green and blue, and each channel is then encrypted into two random phase masks based on the ART and interference method. Light sources with corresponding wavelengths are used to illuminate the retrieved phase-only masks during image decryption. The influence of security parameters on decrypted images is also analyzed. Numerical simulation results are presented to illustrate the feasibility and effectiveness of the proposed method.
    No preview · Article · Sep 2009 · Optics Communications
  • Source
    W. Chen · C. Quan · C.J. Tay · Y. Fu
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    ABSTRACT: Phase-shifting digital holographic technique is a powerful tool for the measurement of various physical parameters, such as object deformation and liquid or cell’s refractive index change. However, for an accurate measurement, phase-shifting error in the reference wave path is still a major issue. In this paper, three novel and simple algorithms are proposed to quantitatively detect and correct phase-shifting error for a pure phase object in two-step phase-shifting digital holography. Influence of phase-shifting error is illustrated, and the effectiveness of the proposed algorithms is demonstrated by numerical simulation results.
    Preview · Article · Jul 2009 · Optics Communications
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    H Shi · Y Fu · C Quan · C J Tay · X He
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    ABSTRACT: A method for the vibration measurement of a micro-electro-mechanical system (MEMS) structure based on digital holographic microscopy (DHM) is presented. A sequence of digital holograms of a vibrating micro-beam excited by varying voltage is captured by a high-speed CCD camera. The phase changes of the object at different instants are obtained by digital reconstruction. The displacement, velocity and acceleration are evaluated by both spatial and temporal Fourier and windowed Fourier analyses. The results show that digital holographic microscopy with Fourier analyses is an effective method for evaluating the dynamic characteristics of a MEMS component.
    Preview · Article · Apr 2009 · Measurement Science and Technology
  • C.J. Tay · C. Quan · W. Chen
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    ABSTRACT: In this paper, complex phasor (CP) method is employed in digital holographic interferometry. Unlike commonly used digital phase subtraction (DPS), the proposed technique processes a CP instead of phase. It is shown that the results obtained by directly filtering the phase produce large errors. It is demonstrated that the phase is not a signal but rather a property of a signal. In addition, the results obtained by the CP method are also compared with those obtained by conventional sine/cosine transformation method.
    No preview · Article · Mar 2009 · Optics & Laser Technology
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    ABSTRACT: Previous study has shown that off-axis illumination (OAI) which employs duplicate conventional source shape such as double dipole, double annular or double quadrupole can reduce the effect of line width fluctuation and process window degradation at the forbidden pitch. In this paper, influence of the new OAI source shape on line end shortening and corner rounding effect is studied. Despite the advantage of reduced line width fluctuation, the proximity effect at line ends and corners for new source shapes need to be examined because both lateral and longitudinal pattern fidelity is important in actual implementation. Simulation study will be used for the study of line end shortening and corner rounding effect using new source shapes and the results will be compared with those resulted from annular illumination. Line end structures such as end to end, staggered, and T-shaped patterns are used for line end shortening study. For corner rounding, L-shaped and U-shaped structure are used. The pattern density and line end separation of feature will be varied to determine the important factors that cause image distortion. Results has shown that new source shapes have similar line end shortening and corner rounding characteristic with the conventional one. Besides, the variation of new source shapes for different pattern density and line end separation is relatively smaller compared with conventional OAI source shapes.
    Full-text · Article · Mar 2009 · Proceedings of SPIE - The International Society for Optical Engineering
  • C. Quan · C. J. Tay · W. Chen
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    ABSTRACT: Digital holography (DH) and digital shearography (DS) both play an important role in non-destructive evaluation. In this paper, a novel method based on digital holographic interferometry (DHI) and complex phasor (CP) is proposed to determine displacement derivative. An algorithm is employed to filter the imaginary and real parts of complex values without the need of direct phase manipulation. Two-dimensional short time Fourier transform (STFT) is employed subsequently to process wrapped phase maps. An experiment is conducted to demonstrate the validity of the proposed method.
    No preview · Article · Mar 2009 · Optics Communications
  • Xiaodong Zhou · Selven Virasawmy · Chenggen Quan
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    ABSTRACT: Benzocyclobutene (BCB) is a thermosetting polymer that can form microfluidics and bond top and bottom layers of the microfluidics at the same time, and yields high repeatability and high bonding strength. This paper reports using photosensitive BCB to fabricate microfluidics and to bond with a thermal press for 4in. wafers. By optimizing the parameters for pattern development and using a three-stage temperature and pressure increment BCB bonding, we realize the whole wafer glass–Si or glass–glass bonding in thermal press without any crack. The wafer-level bonding shows a bonding percentage above 70%, a tensile stress above 4.94MPa, and a bonding repeatability over 95%. Furthermore, the bonding is compatible with thick electrode integration, that microfluidics with 380nm thick electrodes underneath can be well-bonded. Our bonding method much reduces the cost compared with bonding BCB in a wafer bonding machine.
    No preview · Article · Jan 2009 · Microsystem Technologies
  • C.J. Tay · C. Quan · R. Akkipeddi · M. Gopal
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    ABSTRACT: In this paper, we describe a method based on a vertical scanning interferometry (VSI) and a micro-Raman spectroscopy for the evaluation of residual profile and stresses of a InP based free-standing MEMS device. The membrane is designed to satisfy both mechanical and optical requirements for a wavelength division multiplexing (WDM) device. The device evaluated shows that the resulting surface profile deviation and residual stresses induced are within acceptably low levels.
    No preview · Article · Jan 2009
  • M. L. Ling · C. J. Tay · C. Quan · G. S. Chua · Q. Lin
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    ABSTRACT: In lithography, forbidden pitch refers to pitch that suffers degradation in the process window due to the application of off-axis illumination (OAI). Destructive light field interference of diffracted light from a mask at forbidden pitch causes reduction in image contrast and depth of focus (DOF) and limits the pitch range to be patterned. In this paper, a modification to conventional OAI shape is proposed to minimize the effect of forbidden pitch. The modification is based on the interaction of illumination source with pattern density. The modified source employs double annular illumination. Simulation is carried out to investigate the effect of the modified source for one dimensional line and space pattern with a pitch varying from 130 to 500 nm. Results shows that the maximum critical dimension fluctuation is around 3% compared to 13% in conventional annular illumination. Furthermore, the degradation in DOF is within 21% of DOF compared to 49% in conventional annular illumination.
    No preview · Article · Jan 2009 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures