Through-focus scanning-optical-microscope imaging method for nanoscale dimensional analysis
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.Optics Letters (Impact Factor: 3.29). 10/2008; 33(17):1990-2. DOI: 10.1364/OL.33.001990
We present a novel optical technique that produces nanometer dimensional measurement sensitivity using a conventional bright-field optical microscope, by analyzing through-focus scanning-optical-microscope images obtained at different focus positions. In principle, this technique can be used to identify which dimension is changing between two nanosized targets and to determine the dimension using a library-matching method. This methodology has potential utility for a wide range of target geometries and application areas, including nanometrology, nanomanufacturing, semiconductor process control, and biotechnology.
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- "Through-focus scanning optical microscopy (TSOM)         allows conventional optical microscopes to collect dimensional information by combining 2D optical images captured at several through-focus positions, transforming a conventional optical microscope into a 3D metrology tool. TSOM is not a resolution enhancement method but an image comparison method and has been demonstrated through simulations to provide lateral and vertical measurement sensitivity of less than a n anometer. "
Conference Paper: TSV reveal height and dimension metrology by the TSOM method[Show abstract] [Hide abstract]
ABSTRACT: This paper reports on an investigation to determine whether through-focus scanning optical microscopy (TSOM) is applicable to micrometer-scale through-silicon via (TSV) reveal metrology. TSOM has shown promise as an alternative inspection and dimensional metrology technique for FinFETs and defects. In this paper TSOM measurements were simulated using 546 nm light and applied to copper TSV reveal pillars with height in the 3 μm to 5 μm range and diameter of 5 μm. Simulation results, combined with white light interferometric profilometry, are used in an attempt to correlate TSOM image features to variations in TSV height, diameter, and sidewall angle (SWA). Simulations illustrate the sensitivity of Differential TSOM Images (DTI’s) using the metric of Optical Intensity Range (OIR), for 5 μm diameter and 5 μm height TSV Cu reveal structures, for variation of SWA (Δ = 2°, OIR = 2.35), height (Δ = 20 nm, OIR = 0.28), and diameter (Δ = 40 nm, OIR = 0.57), compared to an OIR noise floor of 0.01. In addition, white light interferometric profilometry reference data is obtained on multiple TSV reveal structures in adjacent die, and averages calculated for each die’s SWA, height, and diameter. TSOM images are obtained on individual TSV’s within each set, with DTI’s obtained by comparing TSV’s from adjacent die. The TSOM DTI’s are compared to average profilometry data from identical die to determine whether there are correlations between DTI and profilometry data. However, with several significant TSV reveal features not accounted for in the simulation model, it is difficult to draw conclusions comparing profilometry measurements to TSOM DTI’s when such features generate strong optical interactions. Thus, even for similar DTI images there are no discernible correlations to SWA, diameter, or height evident in the profilometry data. The use of a more controlled set of test structures may be advantageous in correlating TSOM to optical images.
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- "different types of dimensional variations and different magnitudes, a wide variety of target geometries can be used, and the requirement for defining the "Best Focus" is eliminated        "
ABSTRACT: We present a novel optical through-focus scanning optical microscopy (TSOM) method that produces nanoscale dimensional measurement sensitivity using a conventional optical microscope. The TSOM method uses optical information from multiple focal planes for dimensional analysis. The TSOM method can be used for nanoscale dimensional and defect analysis for a wide variety of target geometries and sizes. We present here an application of the method to analyze the size and shape of nanoparticles. We present the analysis based on simulations and also provide experimental data.
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- "This information may be obtained using an appropriate data acquisition and analysis method. Based on this, and on the observation of a distinct signature for different parametric variations, we introduced a new method for nanoscaledimensional analysis with nanometer sensitivity for threedimensional , nanosized targets using a conventional brightfield optical microscope      . The method is referred to as the 'through-focus scanning optical microscopy' (TSOM pronounced as 'tee-som') imaging method. "
ABSTRACT: Through‐focus scanning optical microscopy (TSOM) is a relatively new method that transforms conventional optical microscopes into truly three‐dimensional metrology tools for nanoscale to microscale dimensional analysis. TSOM achieves this by acquiring and analyzing a set of optical images collected at various focus positions going through focus (from above‐focus to under‐focus). The measurement resolution is comparable to what is possible with typical light scatterometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). TSOM method is able to identify nanometer scale difference, type of the difference and magnitude of the difference between two nano/micro scale targets using a conventional optical microscope with visible wavelength illumination. Numerous industries could benefit from the TSOM method—such as the semiconductor industry, MEMS, NEMS, biotechnology, nanomanufacturing, data storage, and photonics. The method is relatively simple and inexpensive, has a high throughput, provides nanoscale sensitivity for 3D measurements and could enable significant savings and yield improvements in nanometrology and nanomanufacturing. Potential applications are demonstrated using experiments and simulations.