To improve the security and efficiency of the image message transmission. This paper propose an optical image encryption scheme based on random phase mask and four-step phase shift digital holography. In the process of image encryption, the low frequency sub-band of the original images are superimposed by wavelet transform to increase the encryption efficiency. In this paper, Henon mapping generates two random phase masks. The initial values and control parameters of Henon mapping can be used as the main keys. The use of random phase mask makes the transmission and storage of the keys of sender and receiver more convenient. Moreover, the wavelength and diffraction distance are also used as the keys, which can enhance the security of encryption. With the help of random phase masks and four-step phase-shifting digital holography, the original image is encrypted into four cipher holograms. The simulation results show that the encryption algorithm proposed in this paper can reconstruct high-quality decrypted images and effectively resist various noise attacks
In the field of unpatterned wafer inspection, the biggest market share is dark field defect inspection, in which the signalto-noise ratio limits the detection limit. In order to improve the signal-to-noise ratio of the optical detection method based on the theory of dark-field scattered light. In this paper, the influence of the polarization characteristic of light on the scattering field is studied, and the signal-to-noise ratio of the scattering signal can be improved by controlling the polarization component of light. The results show that modulating the polarized light can achieve a higher signal-to-noise ratio.
Extreme ultraviolet lithography (EUV) is a key technology for micro-nano processing and is widely used in the chip manufacturing process. Mask optimization is one of the key resolution enhancement techniques in EUV lithography. In this paper, a thick mask optimization method based on particle swarm optimization (PSO) algorithm is proposed to improve simulation accuracy and imaging quality. In this work, we change the calculation order of formulas, which is used to accelerate the imaging calculations. The equivalent film layer method is used to approximate the reflection coefficients of thick mask multilayer film structures to improve the simulation accuracy. The inverse lithography problem for thick mask optimization is solved by particle swarm optimization algorithm. The simulation results show that this method can effectively improve the simulation accuracy and imaging quality.
A mask optimization method based on self-calibrated convolutions is proposed in this paper to reduce the imaging distortion caused by optical proximity effect(OPE). The network model was constructed by combining the inverse lithography technology(ILT), and the parameters of the network model were optimized by the dataset for training. The dataset includes the target pattern and the mask optimized by gradient descent method. The network model based on selfcalibrated convolutions can output an optimized mask according to the target pattern, and the optimized mask is passed through the lithography forward model to obtain the exposure pattern. By the simulation experiment, compared with the traditional gradient-based method, proposed method in this paper has high computational efficiency and small error.
Extreme ultra-violet (EUV) lithography photomask defects are a common problem in the lithography printing process, which has a serious impact on the lithography printing process. Therefore, it is necessary to detect and quickly locate the defect. Many researchers have used image processing and machine learning methods to quickly identify defects in EUV photomasks and subsequently repair them. This paper proposes a detection method based on neural network image segmentation, and we introduce an improved U-Net to predict photomask defects. Our experiments show that the network model has better accuracy. In the process of identifying the defect image, it is in good agreement with the ground truth.
The theory of compressed sensing shows that the original signal can be recovered by low sampling rate, so it is often used in the field of optical imaging. To solve the problem of excessive amount of image data and large computational burden, a new method based on column blocking and mixed blocking method is proposed in this paper. Simulation experiments and comparative analysis show that the proposed column blocking method has improved the quality of image reconstruction to a certain extent, while the mixed blocking method has significantly improved the speed and quality of image reconstruction.
With the development of the integrated circuit manufacturing process, the critical dimension of optical lithography is reduced. Due to the optical diffraction effect, the influence of the distortion of the lithography output pattern on the integrated circuit is gradually increasing. Mask optimization in lithography is a very critical issue. In this paper, a residual network-based mask optimization method is proposed. Using the optimization masks generated by the traditional gradient descent method and its corresponding initial input masks as the training set, the residual network is trained by the inverse lithography optimization process. The parameters of the residual network weight layer are optimized. The optimized results are projected in the forward lithography model to obtain an exposure pattern of the wafer. Compared with the traditional gradient descent method, this method can improve the calculation efficiency and realize the distortion correction of the images generated by lithography.
A three-dimensional profile measurement method based on digital photoelastic fringe analysis technology is proposed in this paper. According to the actual stress field of a disc under appropriate load, the photoelastic fringe patterns are generated. These patterns are illuminated on the reference plane and objects through a projector, which are regarded as the structured-light pattern sequence. Then a series of images including normal images and deformed fringe images are captured. These images contain two significant photoelastic parameters, isoclinic parameter and isochromatic parameter, which could be evaluated by the phase shifting method. Therefore, phase differences can be calculated by photoelastic isochromatic parameter after phase unwrapping. Depth information is carried in the phase differences and virtual 3D profile equal to real objects could be reconstructed. Experiments demonstrate that this method is robust and suitable for measuring objects with regular and general shape.
Wafer surface defect detection plays an important role in product yield improvement. Particles are the main source in the majority of defects on wafer. We calculate and analyze the scattering field around the particles on the un-patterned wafer surface by light scattering method. A model was built to calculate an isolated particle based on Mie theory firstly, and another model was built to calculate particle scattering field on a smooth wafer surface based on Bidirectional Reflectance Distribution Function (BRDF). We simulated the scattering field with different parameters set: incidence angle, polarization state and scattering angle channel. The results verify the feasibility of our method to calculate the scattering field.
The temperature compensation effect of FBG sensors is crucial to their measuring accuracy. In the design of a FBG sensor, two FBGs are often adopted to subject positive and negative strains through two packaging methods including all grating pasting and two-end pasting after grating pretension. Temperature compensation of the FBG sensor is often realized by using the difference of the wavelength shift of the two FBGs as the sensing signal. In current reports, temperature compensation is performed based on the assumption that the wavelength shifts of the two FBGs are the same. However, the difference of the wavelength shift is also influenced by the packaging methods and the temperature changing environment. This work presents an experimental study on the temperature compensation effect of two pair different packaged FBGs under abrupt temperature changing environment. For each packaging method, two FBGs with same parameters are pasted on the upper and lower surfaces of an equal-strength cantilever and assembled in a shell to serve as a FBG sensor. Boiling water and ice-water mixture are used to pour on the shell to form abrupt temperature changing, whereas an adjustable thermostat provides slowly temperature changing environment. Experimental results shows that the temperature compensation effects for the two different packaging method are same(within 21pm) when slowly temperature changing slowly, however, the compensation effects are significantly degraded during abrupt temperature increasing (58 pm and 48 pm for all grating pasting and two-end pasting, respectively). The results can provide a scientific reference for the design of FBG sensors.
In engineering practice, especially in the structural health monitoring (SHM) of civil engineering, the deformation of concrete is usually small, so a strain sensor don’t need a large measuring range but a high sensitivity. This work presents the structural design, measuring and sensitization principle, and full test of an embedded FBG strain sensor for SHM of reinforced concrete. Two capillary steel tubes protected by a stainless steel tube and embedded with each end fiber of a FBG have been proposed, which possesses the capacity of strain sensitization and adjustment. Experimental results show that sensor provides a sensitivity of 4.2 pm/με in measurement range of ±300με, which is 3.5 times than the bare FBG with center wavelength of 1550 nm. Test results also demonstrate that the sensor possesses good repeatability and creep resistance, which is promising for applications in civil engineering.
Hypernumerical aperture and polarized illumination are the key technologies of resolution enhancement of lithography. When the numerical aperture reaches 0.85 and above, especially in the immersion lithography, polarization effect must be taken into consideration. The performance of the projection lens needs to be characterized by rigorous polarization aberration. The vector polarization imaging system that is suitable for hypernumerical aperture is established, and the distortion effects introduced by polarization aberration are analyzed. Orientation Zernike polynomials-based method and Pauli–Zernike polynomials-based method are adopted to parameterize the polarization aberration represented by Jones pupil. Critical dimension error, placement error, and normal int. log slope index are introduced as the index to value imaging distortion. The proposed method and analysis conclusion would provide meaningful guidance for projection lens design of lithographic tools.
For lithographic tools, the forward model of imaging system is repeated many times in the inverse optimization algorithm of optical proximity correction (OPC). Fast and accurate imaging simulation is highly desirable as one of the most critical components in the forward modeling simulations. We have focused on investigating the physical properties of optical imaging in lithography and introduced the method of separation of variables in Mathematical Physics as the fundamental theory to deal with a wide range of process variables. We proposed a rigorous methodology from first principles to speed up image simulations. The proposed imaging formula can be rearranged by two parts, one with only variables, while the remaining part independent with the variables. Simulations for a variety of different process variables confirmed that the proposed method yields a superior quality of image with an accuracy of 10-3 and superior performance of speed. Therefore, the proposed method provides a novel theory and practical means for OPC and other resolution enhancement technologies (RETs) in optical lithography.
The NA of immersion lithography has reached 1.35, in which case polarization effect must be taken into account. The performance of the projection lens should be characterized by polarization aberration. We proposed a polarization aberration measurement theory and method, using the binary grating structure as the mask pattern, with intensity distribution signal as the measuring signal. Pauli Zernike polynomials are adopted to characterizing the polarization aberration, and a linear relationship between intensity signal and Pauli Zernike coefficients was derived. Simulation results show that using the proposed method, the polarization aberration can be reconstructed with relative error of refactoring to 10-2.
Information of lens aberration of lithographic tools is important as it directly affects the intensity distribution in the image plane. Zernike polynomials are commonly used for a mathematical description of lens aberrations. Due to the advantage of lower cost and easier implementation of tools, image based measurement techniques have been widely used. Lithographic tools are typically partially coherent systems that can be described by a bilinear model, which entails time consuming calculations and does not lend a simple and intuitive relationship between lens aberrations and the resulted images. Previous methods for retrieving lens aberrations in such partially coherent systems involve through-focus image measurements and time-consuming iterative algorithms. In this work, we propose a method for aberration measurement in lithographic tools, which only requires measuring two images of intensity distribution. Two linear formulations are derived in matrix forms that directly relate the measured images to the unknown Zernike coefficients. Consequently, an efficient non-iterative solution is obtained.
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