An in situ aberration measurement method using a phase-shift ring mask is proposed for a lithographic projection lens whose numerical aperture is below 0.8. In this method, two-dimensional phase-shift rings are designed as the measurement mask. A linear relationship model between the intensity distribution of the lateral aerial image and the aberrations is built by principal component analysis and multivariate linear regression analyses. Compared with the principal component analysis of the aerial images (AMAI-PCA) method, in which a binary mask and through-focus aerial images are used for aberration extraction, the aerial images of the phase-shift ring mask contain more useful information, providing the possibility to eliminate the crosstalk between different kinds of aberrations. Therefore, the accuracy of the aberration measurement is improved. Simulations with the lithography simulator Dr.LiTHO showed that the accuracy is improved by 15% and five more Zernike aberrations can be measured compared with the standard AMAI-PCA. Moreover, the proposed method requires less measured aerial images and is faster than the AMAI-PCA.
An in situ aberration measurement method using a two dimensional (2D) phase-shift ring mask has been proposed for
lithographic projection lenses, which is more accurate and faster than AMAI-PCA method. The defocus of the aerial
image of the 2D measurement mask is the main source of the measurement error of this method. In this paper, a defocus
measurement method for the aberration measurement method is proposed, in which the residual of the principal
component analysis process is used as the criterion. After the defocus is accurately measured, the most suitable linear
relationship model, which plays a very important role in the aberration measurement method, can be determined.
Simulations with the lithography simulator Dr. LiTHO demonstrated that the accuracy of the defocus measurement
method is approximately 1nm. The aberration measurement method can detect 12 Zernike aberrations (Z5~Z16) with
maximum systematic error of approximately 1mλ, when the suitable linear relationship model is used.
An in situ aberration measurement method using a phase-shift ring mask is proposed for lithographic projection lenses.
Two dimensional (2D) phase-shift rings are designed as the measurement mask. A linear model between the aerial image
intensity distribution and the aberrations is built by principal component analysis and multivariate linear regression
analyses. Compared with the AMAI-PCA method, in which a binary mask and through-focus aerial images at are used
for aberration extraction, the aerial images of the phase-shift ring mask contain more useful information. This provides
the possibility to eliminate the crosstalk between different kinds of aberrations. Therefore, the accuracy of aberration
measurement is improved. Simulations with the lithography simulator Dr. LiTHO showed that the accuracy is improved
by 15% and 5 more Zernike aberrations can be measured compared with AMAI-PCA. Moreover, the speed of aberration
measurement is improved because less aerial images are required using the new 2D mask.
An in situ aberration measurement technique based on an aerial image with an optimized source is proposed. A linear relationship between the aerial image and Zernike coefficients is established by the principal components and regression matrices, which are obtained in a modeling process through principal component analysis (PCA) and regression analysis. The linear relationship is used to extract Zernike aberrations from the measured aerial image in a retrieval process. The characteristics of regression matrix are analyzed, and the retrieval process of Zernike coefficients is optimized. An evaluation function for the measurement accuracy of Zernike aberrations is proposed, and then a fast procedure to optimize the illumination source is designed. Parameters of the illumination source are optimized according to the evaluation function and applied in our method. The simulators Dr.LiTHO and PROLITH are used to validate the method. Compared to the previous aberration measurement technique based on principal component analysis of an aerial image (AMAI-PCA), the number terms of Zernike coefficients that can be measured are increased from 7 to 27, and the measurement accuracy of Zernike aberrations is improved by more than 20%.
In this paper, we propose an aberration metrology (AM) of a lithographic projection lens based on aerial images (AI) by using a quadratic relationship model (Quad) between the aerial-image intensity distribution and the Zernike coefficients. The proposed method (AMAI-Quad) uses principal component analysis and multiple linear regression analyses for model generation. The quadratic model is, then, used to extract Zernike coefficients by a nonlinear least-squares minimizing technique. The best linear constrain condition is estimated by optimizing the illumination settings. Compared with earlier techniques, based on a linear relationship between Zernike coefficients and AIs, the new method can extend the orders of Zernike coefficients measured. The application of AMAI-Quad to AIs, computed by lithography simulators PROLITH and Dr.LiTHO, demonstrated an extension of measurement range to 90mλ and an enhancement of measurement accuracy by more than 30 percent.
A novel technique (AMAI-Quad) for aberration extraction of lithographic projection based on quadratic relationship
model between aerial-image intensity distribution and Zernike coefficients is proposed. Zernike coefficients in this case
represent the imaging quality of lithographic projection lens in a semiconductor wafer exposure scanner. The proposed
method uses principal component analysis and multivariate linear regression analysis for model generation. This
quadratic model is then used to extract Zernike coefficients by nonlinear least-squares. Compared with earlier techniques,
based on a linear relationship between Zernike coefficients and aerial images, proposed by Duan, the new method can
extend the types of aberrations measured. The application of AMAI-Quad to computed images of lithography simulators
PROLITH and Dr.LiTHO for randomly varied wavefront aberrations within a range of 50mλ demonstrated an accuracy
improvement of 30%.
An in-situ aberration measurement technique based on aerial image with optimized source is proposed. A linear
relationship between aerial image and Zernike coefficients is established by principle component analysis and regression
analysis. The linear relationship is used to extract aberrations. The impacts of the source on regression matrix character
and the Zernike aberrations measurement accuracy are analyzed. An evaluation function for the aberrations measurement
accuracy is introduced to optimize the source. Parameters of the source are optimized by the evaluation function using
the simulators Dr.LiTHO and PROLITH. Then the optimized source parameters are adopted in our method. Compared
with the previous aberration measurement technique based on principal component analysis of aerial image
(AMAI-PCA), the number terms of Zernike coefficients that can be measured are increased from 7 to 27, and the
Zernike aberrations measurement accuracy is improved by more than 20%.
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