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Fizeau-type interferometric probe to measure geometrical thickness of silicon wafers.
Jin, Jonghan,Maeng, Saerom,Park, Jungjae,Kim, Jong-Ahn,Kim, Jae Wan Optical Society of America 2014 Optics express Vol.22 No.19
<P>We developed an optical interferometric probe for measuring the geometrical thickness and refractive index of silicon wafers based on a Fizeau-type spectral-domain interferometer, as realized by adopting the optical fiber components of a circulator and a sheet-type beam splitter. The proposed method enables us to achieve a much simpler optical composition and higher immunity to air fluctuations owing to the use of fiber components and a common-path configuration as compared to a bulk-type optical configuration. A femtosecond pulse laser having a spectral bandwidth of 80 nm at a center wavelength of 1.55 µm and an optical spectrum analyzer having a wavelength uncertainty of 0.02 nm were used to acquire multiple interference signals in the frequency domain without a mechanical phase-shifting process. Among the many peaks in the Fourier-transformed signals of the measured interferograms, only three interference signals representing three different optical path differences were selected to extract both the geometrical thickness and group refractive index of a silicon wafer simultaneously. A single point on a double-sided polished silicon wafer was measured 90 times repetitively every two seconds. The geometrical thickness and group refractive index were found to be 476.89 µm and 3.6084, respectively. The measured thickness is in good agreement with that of a contact type method within the expanded uncertainty of contact-type instruments. Through an uncertainty evaluation of the proposed method, the expanded uncertainty of the geometrical thickness was estimated to be 0.12 µm (k = 2).</P>
Precision depth measurement of through silicon vias (TSVs) on 3D semiconductor packaging process.
Jin, Jonghan,Kim, Jae Wan,Kang, Chu-Shik,Kim, Jong-Ahn,Lee, Sunghun Optical Society of America 2012 Optics express Vol.20 No.5
<P>We have proposed and demonstrated a novel method to measure depths of through silicon vias (TSVs) at high speed. TSVs are fine and deep holes fabricated in silicon wafers for 3D semiconductors; they are used for electrical connections between vertically stacked wafers. Because the high-aspect ratio hole of the TSV makes it difficult for light to reach the bottom surface, conventional optical methods using visible lights cannot determine the depth value. By adopting an optical comb of a femtosecond pulse laser in the infra-red range as a light source, the depths of TSVs having aspect ratio of about 7 were measured. This measurement was done at high speed based on spectral resolved interferometry. The proposed method is expected to be an alternative method for depth inspection of TSVs.</P>
Jin, Jonghan,Kim, Jae Wan,Kang, Chu-Shik,Kim, Jong-Ahn The Optical Society 2010 Optics express Vol.18 No.23
<P>We propose and demonstrate a novel method to enhance the visibility of an optical interferometer when measuring low reflective materials. Because of scattering from a rough surface or its own low reflectivity, the visibility of the obtained interference signal is seriously deteriorated. By amplifying the weak light coming from the sample based on an injection-locking technique, the visibility can be enhanced. As a feasibility test, even with a sample having a reflectivity of 0.6%, we obtained almost the same visibility as a metal coated mirror. The suggested visibility enhanced interferometer can be widely used for measuring low reflective materials.</P>
Absolute Distance Measurements Using the Optical Comb of a Femtosecond Pulse Laser
Jonghan Jin,Young-Jin Kim,Yunseok Kim,Seung-Woo Kim 한국정밀공학회 2007 International Journal of Precision Engineering and Vol.8 No.4
We describe a new way of implementing absolute displacement measurements by exploiting the optical comb of a femtosecond pulse laser as a wavelength ruler. The optical comb is stabilized by locking both the repetition rate and the carrier offset frequency to an Rb clock of frequency standard. Multiwavelength interferometry is then performed using the quasi-monochromatic beams of well-defined generated wavelengths by tuning an external cavity laser diode consecutively to preselected light modes of the optical comb. This scheme of wavelength synthesizing allows the measurement of absolute distances with a high precision that is traceable to the definition of time. The achievable wavelength uncertainty is 1.9×<SUP>-10</SUP>, which allows the absolute heights of gauge blocks to be determined with an overall calibration uncertainty of 15 nm (k = 1). These results demonstrate a successful industrial application of an optical frequency synthesis employing a femtosecond laser, a technique that offers many possibilities for performing precision length metrology that is traceable to the well-defined international definition of time.
Thickness and refractive index measurement of a silicon wafer based on an optical comb
Jin, Jonghan,Kim, Jae Wan,Kang, Chu-Shik,Kim, Jong-Ahn,Eom, Tae Bong The Optical Society 2010 Optics express Vol.18 No.17
<P>We have proposed and demonstrated a novel method that can determine both the geometrical thickness and refractive index of a silicon wafer at the same time using an optical comb. The geometrical thickness and refractive index of a silicon wafer was determined from the optical thickness using phase information obtained in the spectral domain. In a feasibility test, the geometrical thickness and refractive index of a wafer were measured to be 334.85 mum and 3.50, respectively. The measurement uncertainty for the geometrical thickness was evaluated as 0.95 mum (k = 1) using a preliminary setup.</P>
Pitch Measurement of 150 ㎚ 1D-grating Standards Using an Nano-metrological Atomic Force Microscope
Jonghan Jin,Ichiko Misumi,Satoshi Gonda,Tomizo Kurosawa 한국정밀공학회 2004 International Journal of Precision Engineering and Vol.5 No.3
Pitch measurements of 150 ㎚ one-dimensional grating standards were carried out using a contact mode atomic force microscopy with a high resolution three-axis laser interferometer. This measurement technique was named as the 'nano-metrological AFM'. In the nano-metrological AFM, three laser interferometers were aligned precisely to the end of an AFM tip. Laser sources of the three-axis laser interferometer in the nano-metrological AFM were calibrated with an I2-stabilized He-Ne laser at a wavelength of 633 ㎚. Therefore, the Abbe error was minimized and the result of the pitch measurement using the nano-metrological AFM could be used to directly measure the length standard. The uncertainty in the pitch measurement was estimated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM). The primary source of uncertainty in the pitch-measurements was derived from the repeatability of the pitch-measurements, and its value was about 0.186 ㎚. The average pitch value was 146.65 ㎚ and the combined standard uncertainty was less than 0.262 ㎚. It is suggested that the metrological AFM is a useful tool for the nano-metrological standard calibration.
정밀질량분석기를 활용한 우레탄폼의 장기열전도도 예측을 위한 분석기법
김진석(Jin Seok Kim),전종한(Jonghan Chun),이진복(Jin Bok Lee),이효진(Hyo-Jin Lee) 대한설비공학회 2010 설비공학 논문집 Vol.22 No.10
A proprietary device is adopted to break out the membrane of cell in the rigid polyurethane foam. As it is known, the membrane of cell is hardly tearing-off thoroughly in a mechanical way due to both its elastic characteristic and micro sized pores. In this study, a novel experimental approach is introduced to burst out all gases inside the cells of the rigid polyurethane foam by abrasively grinding micro-cells completely into fine powder. The biggest advantage of this approach is to be capable of releasing all gases out from the cell even in the micro pores. As clearly reflected from the repeatability, the accuracy of the result is highly improved and high confidence in the data sets as well. For the measurements of not only gas composition but partial pressure for each gas simultaneously as well, a precision gas mass spectrometer is used in-line directly to the abrasive grinding device. To control the starting point of the polyurethane foam, all samples were prepared on site in the laboratory. Manufactured time is one of the most critical factors in characterization of cell gas composition because it is known that one of gas composition, especially, carbon dioxide, is diffused out dramatically in a short period of time as soon as it is foamed.