Metrological sensitivity improvement of through-focus scanning optical microscopy by controlling illumination coherence

Park, Shin-Woong; You, Byeong Geon; Park, Gyunam; Kim, Youngbaek; Lee, Jun Ho; Cho, Joong Hwee; Ye, Yun; Kim, Hwi

doi:10.1364/oe.27.001981

Cited by 3 publications

(1 citation statement)

References 18 publications

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“…The dimensional information of the target is extracted by matching the intensity information with the simulation results in the database. For improving the performance, great attention has been paid to minimizing the dissimilarities between the intensity information acquisition and simulation conditions [12][13][14][15][16][17][18][19]. In the meantime, model-based TSOM utilizes only the optical intensity range and the mean-square intensity information of the TSOM image; hence, large amounts of intensity distribution information correlated to the dimensional information of the targets is ignored.…”

Section: Introductionmentioning

confidence: 99%

MEMS High Aspect Ratio Trench Three-Dimensional Measurement Using Through-Focus Scanning Optical Microscopy and Deep Learning Method

Shi

Gao

et al. 2022

Applied Sciences

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High-aspect-ratio structures have become increasingly important in MEMS devices. In situ, real-time critical dimension and depth measurement for high-aspect-ratio structures is critical for optimizing the deep etching process. Through-focus scanning optical microscopy (TSOM) is a high-throughput and inexpensive optical measurement method for critical dimension and depth measurement. Thus far, TSOM has only been used to measure targets with dimension of 1 μm or less, which is far from sufficient for MEMS. Deep learning is a powerful tool that improves the TSOM performance by taking advantage of additional intensity information. In this work, we propose a convolutional neural network model-based TSOM method for measuring individual high-aspect-ratio trenches on silicon with width up to 30 μm and depth up to 440 μm. Experimental demonstrations are conducted and the results show that the proposed method is suitable for measuring the width and depth of high-aspect-ratio trenches with a standard deviation and error of approximately a hundred nanometers or less. The proposed method can be applied to the semiconductor field.

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Section: Introductionmentioning

confidence: 99%

MEMS High Aspect Ratio Trench Three-Dimensional Measurement Using Through-Focus Scanning Optical Microscopy and Deep Learning Method

Shi

Gao

et al. 2022

Applied Sciences

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Motion-free TSOM using a deformable mirror

et al. 2020

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Through-focus scanning optical microscopy (TSOM) is a model-based optical metrology method that involves the scanning of a target through the focus of an optical microscope. Unlike a conventional optical microscope that directly extracts the diffraction-limited optical information from a single in-focus image, the TSOM method extracts nanometer scale sensitive information by matching the target TSOM data/image to reference TSOM data/images that are either experimentally or computationally collected. Therefore, the sensitivity and accuracy of the TSOM method strongly depends on the similarities between the conditions in which the target and reference TSOM images are taken or simulated, especially the lateral instability during through-focus scanning. As a remedy to the lateral instability, we proposed the application of adaptive optics to the through-focus scanning operation and initially developed a closed-loop system with a tip/tilt mirror and a Shack-Hartmann sensor, with which we were able to keep the plane position within peak-to-valley (PV) 33 nm. We then further developed a motion-free TSOM tool reducing the instability down to practically zero by the replacement of the tip/tilt mirror with a deformable mirror that performs through-focus scanning by deforming its mirror surface. The motion-free TSOM tool with a × 50 (NA 0.55) objective lens could provide a scanning range of up to ± 25 µm with a minimum step of 25 nm at a maximum update rate of 4 kHz. The tool was demonstrated to have a recognition accuracy of < 4 nm for critical dimension (CD) values in the range of 60 ∼ 120 nm with a reference TSOM image library generated by a Fourier modal method matching various observations conditions.

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Defect height estimation via model-less TSOM under optical resolution

et al. 2021

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We propose a new method of through-focus scanning optical microscopy (TSOM) without a reference database, i.e., a model-less TSOM method. Building a TSOM reference database is time-consuming or even impractical in some TSOM applications that involve complex structures, such as 3D NAND, or irregular shapes such as defects. The proposed model-less TSOM method was used to determine just the height of defect particles, for the first time as far as we are aware. Defect height is the only relevant dimension for the display panel application. Specifically, we analyzed 40 organic light-emitting diode (OLED) surface defects using a lab-developed motion-free TSOM tool consisting of a 50× objective lens (numerical aperture (NA) 0.55), a 532-nm light source, an imaging detector with a 7.5-µm pitch, and a deformable mirror. The tool is in-line and capable of achieving high throughput non-destructively, both relevant features for industrial applications. We investigated linear regression relations between newly defined TSOM parameters (TSOM height, TSOM area and TSOM volume) and the defect heights, which were first measured by atomic force microscopy (AFM). Following defect classification based on in-focus images, we successfully found that the AFM height has a linear correlation with 50% TSOM height (H50%) within ± 20.3 nm (1σ) error over the range of 140 to 950 nm. The one-sigma error, i.e., 20.3 nm, was approximately λ/26 or 1/43 of the depth of focus (DOF) of the applied microscope.

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Metrological sensitivity improvement of through-focus scanning optical microscopy by controlling illumination coherence

Cited by 3 publications

References 18 publications

MEMS High Aspect Ratio Trench Three-Dimensional Measurement Using Through-Focus Scanning Optical Microscopy and Deep Learning Method

MEMS High Aspect Ratio Trench Three-Dimensional Measurement Using Through-Focus Scanning Optical Microscopy and Deep Learning Method

Motion-free TSOM using a deformable mirror

Defect height estimation via model-less TSOM under optical resolution

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