Qiongyan Yuan

Coma measurement by use of an alternating phase-shifting mask mark with a specific phase width

The correlation between the coma sensitivity of the alternating phase-shifting mask (Alt-PSM) mark and the marks structure is studied based on the Hopkins theory of partially coherent imaging and positive resist optical lithography (PROLITH) simulation. It is found that an optimized Alt-PSM mark with its phase width being two-thirds its pitch has a higher sensitivity to coma than Alt-PSM marks with the same pitch and the different phase widths. The pitch of the Alt-PSM mark is also optimized by PROLITH simulation, and the structure of p=1.92lambda/NA and pw=2p/3 proves to be with the highest sensitivity. The optimized Alt-PSM mark is used as a measurement mark to retrieve coma aberration from the projection optics in lithographic tools. In comparison with an ordinary Alt-PSM mark with its phase width being a half its pitch, the measurement accuracies of Z(7) and Z(14) apparently increase.

Coma measurement of projection optics in lithographic tools based on relative image displacements at multiple illumination settings

In this paper, we propose a novel method for measuring the coma aberrations of lithographic projection optics based on relative image displacements at multiple illumination settings. The measurement accuracy of coma can be improved because the phase-shifting gratings are more sensitive to the aberrations than the binary gratings used in the TAMIS technique, and the impact of distortion on displacements of aerial image can be eliminated when the relative image displacements are measured. The PROLITH simulation results show that, the measurement accuracy of coma increases by more than 25% under conventional illumination, and the measurement accuracy of primary coma increases by more than 20% under annular illumination, compared with the TAMIS technique.

Common characteristics shared by different differential phase contrast imaging methods

There are many variations of differential phase contrast imaging methods. Although these imaging methods are different in configuration, they are alike in imaging by extracting differential phase information through the evaluation of the refraction angles. In this paper, we investigate common characteristics shared by various different differential phase contrast imaging methods.

Aberration induced intensity imbalance of alternating phase shifting mask in lithographic imaging

We discuss the aberration-induced intensity imbalance of alternating phase-shifting mask (Alt-PSM) in lithographic imaging, in contrast to numerous studies on mask-induced intensity imbalance. Based on the Hopkins theory of partial coherent imaging, a linear relationship between the intensity difference of adjacent peaks in an Alt-PSM image and even aberration is established by formulations and verified by numerical results. The application of the linear relationship is briefly discussed.

Translational-symmetry alternating phase shifting mask grating mark used in a linear measurement model of lithographic projection lens aberrations

A linear measurement model of lithographic projection lens aberrations is studied numerically based on the Hopkins theory of partially-coherent imaging and positive resist optical lithography (PROLITH) simulation. In this linearity model, the correlation between the marks structure and its sensitivities to aberrations is analyzed. A method to design a mark with high sensitivity is proved and declared. By use of this method, a translational-symmetry alternating phase shifting mask (Alt-PSM) grating mark is redesigned with all of the even orders, +/-3rd and +/-5th order diffraction light missing. In the evaluation simulation, the measurement accuracies of aberrations prove to be enhanced apparently by use of the redesigned mark instead of the old ones.

Analysis of Absorption and Phase Difference Images from Differential Interference Contrast Microscopy

Extraction of phase and amplitude information in differential interference contrast (DIC) microscopy is a challenging but stimulating task. In this paper, a simple straightforward non‐iterative method to extract the absorption and phase difference images for DIC is presented. According to the method proposed in [1], phase information can be acquired straightforwardly. The feasibility of our method is confirmed by experimental results of imaging liquid paraffin drops using a commercial DIC microscope. Compared with the available methods and previous research [1–4], our approach simplifies the procedures to extract the absorption and phase difference images without weak absorption limit.

Odd aberration measurement of projection optics in lithographic tools based on dipole illumination

Theoretical analysis of impact of illumination profile on measurement accuracy is given. A novel measurement technique using Alt-PSM marks under dipole illumination is proposed based on the analysis result.

Aberration measurement of lithographic projection lens by using a translational symmetry Alt-PSM grating mark

A method to design a mark with high sensitivity is proved and declared. A translational symmetry Alt-PSM grating mark is redesigned with all of the even orders, ±3rd and ±5th orders diffraction light missing.

High-Accuracy Measurement of Coma with the Optimized Alternating Phase-shifting Mask with a Specific Phase Width

The correlation between the coma sensitivity of the Alternating Phase-Shifting Mask (Alt-PSM) and the Alt-PSMs structure is studied. It is found that an optimized Alt-PSM whose phase width is two thirds of its pitch has a higher sensitivity to coma than Alt-PSMs with the same pitch and the different phase widths, when the pitch of the Alt-PSM makes only +/-1 and +/-3 orders diffraction light enter the lens pupil. The optimized Alt-PSM is used as a measurement mark to retrieve coma aberration from the projection optics in lithographic tools. In comparison with an ordinary Alt-PSM mark whose phase width is a half of its pitch, the measurement accuracies of Z7 and Z14 have increased by 15% and 31% respectively.

A novel method for measuring the coma aberration of lithographic projection optics by relative image displacements at multiple illumination settings

As the critical dimension shrinks, deterioration of image quality caused by coma aberrations of the lithographic projection optics has become a serious problem in optical lithography. Fast and accurate in-situ measurement techniques for measuring the coma aberration are necessary. In the present paper, we propose a novel method for measuring the coma aberrations of lithographic projection optics by use of a novel mark, which is composed of two fine-segmented phase-shifting gratings and two sufficiently large binary gratings. The coma aberration is extracted from the relative displacements between the phase-shifting gratings and the binary gratings at multiple illumination settings. The PROLITH simulation results show that compared with the TAMIS technique, the measurement accuracy of coma aberration increases by more than 34% under conventional illumination, and the measurement accuracy of low-order coma aberration increases by more than 28% under annular illumination.