Ph.D. Optical Science and Engineering
M.S. Electrical Engineering
B.E. Electronics Engineering
RESEARCH INTERESTS
Integration of Technologies, Information Science, Data Modeling,
8
Scopus Publications
Scopus Publications
Absolute thickness measurement of silicon wafer using wavelength scanning interferometer Young-Sik Ghim, Amit Suratkar, Angela Davies, Yun-Woo Lee Proceedings of SPIE the International Society for Optical Engineering, 2011 Wavelength scanning interferometry based on a reflectometry model is proposed for measuring the absolute thickness profile of a thin silicon wafer. A Fourier-based method of wavelength scanning interferometry is limited to thicker wafers because of a tuning range limitation of the source. As an example, the minimum thickness measurable with the conventional Fourier-based technique using a 4 nm-tunable (500 GHz) 1550 nm laser is approximately 170 μm. Our proposed method enables an extension of thickness measurements with a reduction in systematic measurement error, representing a significant advance. The so-called 'ripple-error' or 'fringe-bleed through' is much lower with a reflectometry-based analysis compared to a Fourier-based analysis. Our method was verified by measuring and testing several wafers with various thicknesses.
Reflectometry-based wavelength scanning interferometry for thickness measurements of very thin wafers Young-Sik Ghim, Amit Suratkar, Angela Davies Optics Express, 2010 With the development of microelectronics, the demand for silicon wafers is greatly increased for various purposes, especially the use of thin wafers for smart cards, cellular phones and stacked packages. In this paper, we describe an innovative scheme of combining wavelength scanning interferometry (4 nm tuning range centered at 1550 nm) with spectroscopic reflectometry that enables us to measure the thickness profile of thin wafers below 100 microm with high thickness resolution. The performance of this method is compared with that of an existing technique and verified by measuring several thin wafers.
Interferometric technique for faceted microstructure metrology using an index matching liquid Daryl Purcell, Amit Suratkar, Angela Davies, Faramarz Farahi, Heidi Ottevaere, Hugo Thienpont Applied Optics, 2010 Microstructured optical products are becoming more widespread due to advances in manufacturing. Many of these structures contain faceted surfaces with steep slopes. Adequate metrology for such surfaces is lacking. We describe an interferometric technique that combines plane wave illumination with an index matching liquid to achieve high quality, high speed measurements of such faceted microstructures. We account for refraction at the interfaces, rather than consider only optical path length changes due to the index liquid, and this significantly improves the facet angle measurement. We demonstrate the technique with the measurement of an array of micropyramids and show that our results are in good agreement with measurements taken on a contact profilometer. We also extend the technique to measure opaque microcorner cubes by implementing an intermediate replication step.
Absolute length (thickness) measurements using wavelength scanning interferometry Proceedings of the 23rd Annual Meeting of the American Society for Precision Engineering Aspe 2008 and the 12th Icpe, 2008
Uncertainty analysis on the absolute thickness of a cavity using a commercial wavelength scanning interferometer Amit Suratkar, Young-Sik Ghim, Angela Davies Proceedings of SPIE the International Society for Optical Engineering, 2008 Wavelength scanning interferometry offers many advantages over traditional phase shifting interferometry, most significantly the elimination of mechanical movement of the part/s for phase modulation by implementing a tunable light source. Further, Fourier analysis on the interference time history enables this technique to accurately measure distances, treating the distance between two optical surfaces as an interferometric cavity. We propose to evaluate the uncertainty in the thickness measurement of a transparent cavity using a commercial Fizeau wavelength scanning interferometer. This work follows the theory and measurement performed in a previous manuscript of measuring absolute distances of opaque objects using a commercial wavelength scanning interferometer. The limits in measuring a cavity using the commercial wavelength scanning interferometer depend on many factors such as temperature variations that affect the test and reference cavity, uncertainty in the reference cavity calibration, tuning rate non-linearities, etc. In addition to an analytical approach, a simulation is described to better understand the measurement process and the uncertainty associated in measuring absolute distances (thickness) of cavities. Preliminary experimental results on the absolute thickness of a transparent cavity are reported along with uncertainty sources.
New interferometric technique to measure the length (thickness) of opaque objects using a commercial interferometer Amit R. Suratkar, Angela D. Davies, Faramarz Farahi Proceedings of SPIE the International Society for Optical Engineering, 2007 Wavelength scanning interferometry offers many advantages over traditional phase shifting interferometry, most significantly the elimination of mechanical movement of the part/s for phase modulation by implementing a tunable light source. Further, Fourier analysis on the interference time history enables this technique to accurately measure distances, treating the distance between two optical surfaces as an interferometric cavity. We propose to use a newly acquired wavelength scanning Fizeau interferometer from Zygo Corporation, the MST (Multiple Surface Transform) to explore the limits of absolute thickness metrology to measure an opaque cavity, such as a gauge block. While transparent cavities can be measured with ease in a Fizeau setup, opaque cavities need additional optics. A two mirror Sagnac configuration in conjunction with the interferometer from Zygo Corporation is used to measure the length (thickness) of a 1 inch gauge block. Current gauge block measurements rely on comparison methods to determine the fractional length with respect to a reference or master gauge block or use techniques which require the absolute length of the gauge block to be previously known. By using wavelength scanning interferometry, the absolute length of the gauge block can be determined directly within limits of the repeatability of the instrument. While other techniques implement a point by point approach for measurement or use interpolation methods, we simply use a large aperture to provide the thickness variation over the sample. Experimental results of a 1 inch gauge block along with an uncertainty estimate are discussed.
Uncertainty analysis on the absolute thickness of a cavity using wavelength shifting interferometry Amit R. Suratkar, Angela A. Davies Optics Infobase Conference Papers, 2006 Wavelength shifting interferometry is implemented to determine the absolute thickness of a cavity. We propose to perform a general uncertainty analysis on the thickness of a Zerodur block and determine the major contributors towards uncertainty.
Measuring the wavefront distortion of a microlens array using an index matching liquid Daryl Purcell, Amit Suratkar, Angela Davies, Faramarz Farahi Optics Infobase Conference Papers, 2006 This paper describes a method in which the overall geometry and form errors of each lens in a microlens array are measured simultaneously by the use of a planar wave.
