• Current Optics and Photonics
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• 제1권5호
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• pp.505-513
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• 2017

Measuring the thickness of thin films is strongly required in the display industry. In recent years, as the size of a pattern has become smaller, the substrate has become larger. Consequently, measuring the thickness of the thin film over a wide area with low spatial sampling size has become a key technique of manufacturing-yield management. Interferometry is a well-known metrology technique that offers low spatial sampling size and the ability to measure a wide area; however, there are some limitations in measuring the thickness of the thin film. This paper proposes a method to calculate the thickness of the thin film in the following two steps: first, pre-estimation of the thickness with the phase at the peak position of the interferogram at the bottom surface of the thin film, using white-light phase-shift interferometry; second, accurate correction of the measurement by fitting the interferogram with the theoretical pattern through the estimated thickness. Feasibility and accuracy of the method has been verified by comparing measured values of photoresist pattern samples, manufactured with the halftone display process, to those measured by AFM. As a result, an area of $880{\times}640$ pixels could be measured in 3 seconds, with a measurement error of less than 12%.

• 한국정밀공학회지
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• 제23권9호
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• pp.102-110
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• 2006

We discuss two possibilities of using femtosecond pulse lasers as a new interferometric light source for enhanced precision surface-profile metrology. First, a train of ultra-fast laser pulses yields repeated low temporal coherence, which allows unequal-path scanning interferometry, which is not feasible with white light. Second, the high spatial coherence of femtosecond pulse lasers enables large-sized optics to be tested in nonsymmetric configurations with relatively small-sized reference surfaces. These two advantages are verified experimentally using Fizeau and Twyman-Green type scanning interferometers.

• 한국군사과학기술학회지
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• 제9권3호
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• pp.109-115
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• 2006

The investigation of the polarization cross-coupling in fiber coils was made using white light Michelson interferometer. The white light interferometer has a light source of about 13nm spectral bandwidth and measurement resolution of less than -80dB. The measurement found that the 200m fiber coil has a polarization cross-coupling of about -64dB in average and -46dB in maximum.

• 한국광학회지
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• 제16권4호
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• pp.319-325
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• 2005

고속으로 간섭피크의 위치를 찾기 위해 일련의 아날로그 신호처리를 수행하는 백색광간섭(WLI)센서용 신호처리 방식을 고안하고, 이를 WLI 온도센서 시스템에 적용하였다. 새로운 신호처리방식을 적용한 결과 잡음은 $0.019^{\circ}C/\sqrt{Hz}$로 측정되었으며, 선형성도 우수하였다. 그러나 보상용 간섭계에서의 온도변화가 센서출력의 드리프트로 나타났으며, 현재의 구성에서 드리프트의 온도 의존성은 $1.42{\mu}m/^{\circ}C$인 것으로 계산되었다. 또한 간섭피크간 간격이 광원의 가간섭길이에 비해 충분히 넓지 않은 경우 간섭무늬 피크의 간격과 신호처리기가 측정한 피크 간격과의 관계가 비선형적으로 나타날 수 있음도 확인하였다.

• 한국광학회지
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• 제12권5호
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• pp.362-370
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• 2001

간섭계의 수차는 물체광과 기준광이 서로 상쇄하는 것으로 알려져 있지만, 물체가 기울어진 경우 완벽한 상쇄가 이루어지지 않아 간섭무늬에 영향을 준다. 본 논문에서는 수치 해석을 통해 이 현상이 백색광 주사 간섭무늬의 두 정점 중, 위상 정점에 직접적인 영향을 주어 오차로 작용함을 보인다. 위상 정점은 가시도 정점에 비하여 높은 분해능과 외란에 대해 강인한 반면, 광학계의 수차에 의해 차수 계산의 부정확함이 유발되고, 측정 정밀도가 떨어지는 단점을 갖는다. 두 정점의 차이 값 계산을 실험한 결과, 위상 정점은 100nm 수준의 오차를 갖고, 특히 그 오차가 광학계의 정렬 오차에 기인함을 보인다.

• 한국광학회지
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• 제11권6호
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• pp.395-399
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• 2000

백색광 간섭계에서는 신속하고 그리고 정확하게 주사방향의 간섭무늬 봉우리점을 추출하는 것이 중요한 관건이다. 봉우리점 산출 속도 향상을 목표로 하여 많은 연구가 진행되어 왔지만, 본 연구에서는 가장 간단한 셈법을 이용하여 기준 시료가 얼마나 정확하게 재구성 되는가를 비교 검토하였다. 두 방법 모두 nm 수준의 정밀도로 단차를 측정할 수 있었는데 역상관을 이용한 셈법이 표면 구조나 수직한 면의 재구성에 더 충실한 결과를 산출함이 관찰되었다.

• Journal of the Optical Society of Korea
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• 제3권2호
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• pp.35-40
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• 1999

One of main error sources in white light scanning interferometry is the inaccuracy of scanning mechanisms in that PZT(piezoelectric transducer) micro-actuators are preferably used. We propose a new calibration method that is capable of identifying actual scanning errors directly by analyzing the spectral distribution of sampled interferograms. This calibration provides an effective means of self-compensation for the non-linearity errors caused by PZT hysteresis, enhancing the measurement uncertainty to a level of 5 nanometers over an entire measuring range of 100 ${\mu}{\textrm}{m}$.

• 한국기계가공학회지
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• 제10권2호
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• pp.104-109
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• 2011

I present a method of aspheric surface profile measurement using 2nd derivative of local area profile. This method is based on the principle of curvature sensor which measures the local 2nd derivative under test along a line. The profile is then reconstructed from the data on the each point. Unlike subaperture-stiching method and slope detection method, 2nd derivative method has strong points from a geometric point of view in measuring the aspheric surface profile. The second derivative terms of surface profile is an intrinsic property of the test piece, which is independent of its position and tip-tilt motion. The curvature is measured at every local area with high accuracy and high lateral resolution by using White-light scanning interferometry.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.424-428
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• 2005

This paper shows a non-contact optical method to inspect micron scale parts which will be manufactured in micro-factory system. This inspection system should have some characteristics like a small size, flexibility, and high measuring speed. In the viewpoint of measuring capabilities, it also has resolution under micron scale with measuring range over millimeter scale. Two methods will be presented in this paper, one is Moire and the other is white-light scanning interferometry. Also some experimental results will be presented to show the possibilities of the proposed inspection system.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 동계학술발표회 논문집
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• pp.17-18
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• 2007