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5 June 2013 Simultaneous measurement of the thickness profile and refractive index distribution of silicon wafers
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Abstract
We describe a method to simultaneously measure both thickness profile and refractive index distribution of a silicon wafer based on a lateral scanning of the wafer itself. By using dispersive interferometer principle based on a broadband source, which is a femtosecond pulse laser with 100 nm spectral bandwidth, both thickness profile and refractive index distribution can be measured at the same time using a single scanning operation along a lateral direction. The proposed measurement system was tested using an approximately 90 mm range with a 0.2 mm step along the center-line, except for the rim area in a ϕ100 silicon wafer. As a result, the thickness profile was determined to have a wedge-like shape with an approximately 2 μm difference at an averaged thickness of 478.03 μm. Also, the mean value of the refractive index distribution was 3.603, with an rms value of about 0.001. In addition, the measurement uncertainty of the thickness profile was evaluated by considering two uncertainty components that are related to the scanning operation, like the yaw motion of the motorized stage and the long-term stability of an optical path difference in an air path. The measurement reliability of both the thickness profile and refractive index distribution can be increased through several methods such as an analysis of the correlation between the thickness profile and the refractive index distribution and a comparative measurement using a contact-type method; these potential methods are the subject of our future work.
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Jungjae Park, Jonghan Jin, Jae Wan Kim, Chu-Shik Kang, and Jong-Ahn Kim "Simultaneous measurement of the thickness profile and refractive index distribution of silicon wafers", Proc. SPIE 8706, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXIV, 87060V (5 June 2013); https://doi.org/10.1117/12.2014799
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