13 May 2015 Inspection of mechanical and electrical properties of silicon wafers using terahertz tomography and spectroscopy
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Abstract
Two different THz applications in the semiconductor industry were explored and validated against established reference measurement techniques and simulations. The first application investigated the possibility of measuring mechanical deformation behaviour of silicon wafers. Time-domain THz tomography mapping scans were carried out to measure wafer thickness and flatness, both in the native state and under different external mechanical loads. These measurements were carried out for a variety of wafers, and the ensuing deformation maps used to validate newly developed numerical simulation models for wafer deformation, and vice versa. In the second part of this paper, carrier dynamics of optically injected charges were investigated by THz spectroscopy. THz pump/probe measurements were carried out in transmission and reflection arrangements on silicon wafers illuminated by a metal halide light source. The light source generates free charge carriers in the semiconductor material that affect the transmission and reflection properties of the semiconductor material. The results of the THz measurements are compared to established standard techniques, like microwave-detected photo-conductance decay (MWPCD) or quasi-steady-state photo conductance (QSSPC) measurements. The defective areas identified with the THz measurements are in good agreement with the defective areas identified by the reference methods. A common benefit of time-domain THz measurements is that the wafer thickness, which is an important measure for the interaction volume of the THz radiation with the semiconductor material, can be calculated from the time- domain signals. The results indicate that THz spectroscopy and imaging can be valuable tools for defect analysis and quality control of silicon wafers, especially since the measurement is fully contact-free and can determine mechanical and electrical properties within a single modality.
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Thomas Arnold, Thomas Arnold, Wolfgang Muehleisen, Wolfgang Muehleisen, Johannes Schicker, Johannes Schicker, Christina Hirschl, Christina Hirschl, } "Inspection of mechanical and electrical properties of silicon wafers using terahertz tomography and spectroscopy", Proc. SPIE 9483, Terahertz Physics, Devices, and Systems IX: Advanced Applications in Industry and Defense, 94830W (13 May 2015); doi: 10.1117/12.2176999; https://doi.org/10.1117/12.2176999
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