Mr. Jaeseok Bae Profile

Jaeseok Bae

at Univ of Science and Technology

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Publications (3)

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Proceedings Article | 3 October 2022 Presentation + Paper

An interferometric method for simultaneous measurement of thickness, refractive index, and surface profile of a silicon wafer

Jungjae Park, Jaeseok Bae, Jonghan Jin

Proceedings Volume 12221, 122210R (2022) https://doi.org/10.1117/12.2632346

KEYWORDS: Refractive index, Semiconducting wafers, Silicon, Interferometers, Wafer-level optics, Optical testing, Mirrors, Integrated optics, Beam splitters, Statistical analysis

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We propose an optical system capable of simultaneously measuring physical thickness, group refractive index, and surface profile of a single-layer substrate based on a spectral domain interferometer. Specifically, the proposed method can be functionally divided into two parts; one is the Mach-Zehnder configuration for thickness and refractive index measurements, the other is the Michelson configuration for surface profile measurement. To integrate two different configurations into a single system, two fiber components of an optical circulator and a 2-by-1 optical coupler were installed for the purpose of acquiring both signals reflected from and transmitted through the sample. In addition, the Michelson configuration was realized by replacing a right-angle turning mirror with a beamsplitter and adding a reference mirror in the Mach-Zehnder layout. For feasibility test of the proposed method, a 100-mm-diameter silicon wafer was laterally scanned within a square area of 50 mm2 using a two-axis motorized linear stage. The reference mirror for surface profile measurement was suitably positioned along the optical axis to prevent the overlap between the optical path differences. As a result, the distribution maps of physical thickness, group refractive index, and surface profile were successfully measured over the target area of the silicon wafer. In the proposed setup, the measured surface profile of a plane-parallel substrate like a silicon wafer represents the bending information in its natural state. The proposed method is highly applicable to the semiconductor or display devices inspection where thickness and surface profile measurement should be monitored simultaneously.

Proceedings Article | 21 June 2019 Paper

Precise thickness measurement and comparison of step-shaped microfluidic channel mold using optical interferometry

Jungjae Park, Jaeseok Bae, Jonghan Jin

Proceedings Volume 11056, 110561R (2019) https://doi.org/10.1117/12.2525970

KEYWORDS: Refractive index, Silicon, Semiconducting wafers, Microfluidics, Interferometers, Optical interferometry, Profilometers, Optical testing

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Optical interferometry is one of the suitable methods which can be used to measure the physical thicknesses of microscale structures because this approach can measure optical path differences accurately with a non-contact method. In this paper, on the basis of the simultaneous measurement of the physical thickness and refractive index of an optically transparent plane-parallel plate, a spectral-domain interferometer capable of measuring the physical thickness and refractive index of separate layers in a step-shaped structure with two layers was proposed and realized. For a feasibility test, a microfluidic channel mold with two layers was selected as a sample. For verification of the measured thickness in a double-layered region, a contact-type surface profilometer equipped with laser interferometers on the x-y-z axes was used for a thickness comparison. However, it is never simple to compare measured thicknesses due to positioning errors and the different measuring sizes of each method. For these reasons, the corresponding thickness value was defined as an offset between height values at center points of the single-layered and double-layered region in a specific area of 5 mm × 5 mm. For an accurate determination of the offset, the slopes of the surface profile were removed. The assumption that the surface profile of the bottom layer in the double-layered region is very flat was applied to calculate the thickness from the measured surface profile, and this assumption was checked as to whether it is acceptable or not in this study. In conclusion, the physical thicknesses according to a surface profilometer and by the proposed method were determined to be 106.332 μm and 106.304 μm, respectively, in good agreement within the respective uncertainty values.

Proceedings Article | 21 June 2019 Paper

Analysis of measurement error caused by swing motion for determining the physical thickness and group refractive index of a large glass panel

Jonghan Jin, Jaeseok Bae, Jungjae Park

Proceedings Volume 11056, 1105604 (2019) https://doi.org/10.1117/12.2525670

KEYWORDS: Glasses, Refractive index, Error analysis, Interferometers, Motion measurement, Light sources, Optical interferometry, Motion analysis, Inspection, Mathematical modeling

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The optical interferometry is a non-contact dimensional measurement technique which is capable of ultra-high-precision measurements. Fundamentally, it provides the optical path difference instead of the geometrical path difference. For thickness measurements of glass panels, the physical thickness can be extracted from the optical thickness when the refractive index of the glass panel is precisely given. Otherwise, the precision of an optical interferometer cannot be maintained owing to errors in the refractive index. To overcome this problem, several studies based on optical interferometry for simultaneously measuring the physical thickness and refractive index have been proposed and realized. For in-line inspections, the vibration problem becomes serious with increased dimensions of thin glass panels. When delivering large glass panels, a large amount of vibration is inevitable. In this paper, a transmission-type spectral-domain interferometer for determining physical thicknesses and group refractive indices of large glass panel, which can be operated even under vibration conditions is introduced. For an in-line inspection, large tilt angles of glass panels are created by swing motion when delivering these glass panels at a high-speed. Even if the proposed method determines physical thickness values successfully under the severe vibration condition used here, the measurement error caused by the vibration effect should be investigated and analyzed to correct the measured thickness values. To do this, a theoretical analysis of the error was performed by mathematical modeling. Moreover, the error of the physical thickness was experimentally analyzed at various tilt angles of the large glass panel. The uncertainty was evaluated to be about 436 nm based on the results of these investigations.

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