Scatterometrie
Introduction |
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The term scatterometry summarizes multiple non-imaging optical measurement methods used to reconstruct periodic structures down to nanometer size, i.e. below the optical Abbe-limit. Scatterometry has proved to be a powerful technique for CD and profile metrology and has established itself as one of the mainly applied methods for CD metrology in semiconductor industry.
Principle of operation |
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Scatterometry measures the reflected/scattered light from the sample to be analyzed. It is very closely related to the method of reflectometry but uses polarization as additional information channel. This way structures that cannot be imaged with a standard microscopic measurement setup can be reconstructed [1]. This demanding task is achieved by solving the so called inverse problem: the structure parameters to be identified are obtained by comparing measured and simulated spectra and minimizing the difference between both by adapting the simulation model [2].
For the scatterometric measurements there are different common setups, which often only differ in the measurands and measurement-parameters. The most important setups are depicted in the following image.
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Fig. 1: Different scatterometric configurations |
Applications |
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The ITO has a commercial spectroscopic ellipsometer (UVISEL by Horiba Jobin Yvon). With this tool scatterometric measurements can be performed. The incident and exit angle can be varied and a wavelength dependent (spectral) measurement of different measurands can be obtained. It is used to characterize optical constants of materials as well as the thickness of single layers in multilayer stacks.
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Fig. 2: Spectroscopic Ellipsometer (Uvisel by Horiba Jobin Yvon) |
Additionally a setup combining white light interferometry and Fourier scatterometry has been built which is used to characterize sub-lambda periodic nanostructures [2-3].
Simulation |
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For the simulation of scatterometric measurements we use the simulation tool MicroSim [4] which has been developed at our institute. MicroSim simulates the optical diffraction of periodic structures using the RCWA (rigorous coupled wave analysis) method [5].
Current research topics |
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Our current research topics, in cooperation with different industrial partners, deal with the influence of line-edge roughness [6-8] on the scatterometric measurements as well as possibilities to extend, improve and investigate the limits [9-10] of current scatterometric measurement setups, with emphasis on future semiconductor industry applications.
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| Fig. 3: A complex model of a rough line with different structure parameters |
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Fig. 4: Measured and simulated pupil images for a white light interference Fourier scatterometry measurement of a silicon line grating of 200 nm line width. |
References |
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| [1] |
T. Schuster, S. Rafler, W. Osten, P. Reinig, T. Hingst, "Scatterometry from crossed grating structures in different configurations", Proc. SPIE 6617, 661715-1 – 661715-9 (2007) |
| [2] |
Ferreras Paz, V., Peterhänsel, S., Frenner, K., & Osten, W. (2012). Solving the inverse grating problem by white light interference Fourier scatterometry. Light: Science & Applications. (accepted for publication) |
| [3] |
Ferreras Paz, V., Peterhansel, S., Frenner, K., Osten, W., Ovsianikov, A., Obata, K., & Chichkov, B. (2011). Depth sensitive Fourier-Scatterometry for the characterization of sub-100 nm periodic structures. Proceedings of SPIE (Vol. 8083, p. 80830M–80830M–9). doi:10.1117/12.889439 |
| [4] |
M. Totzeck: „Numerical simulation of high-NA quantitative polarization microscopy and corresponding near-fields", Optik 112 (9), 399-406 (2001) |
| [5] |
T. Schuster, J. Ruoff, N. Kerwien, S. Rafler, W. Osten, "Normal vector method for convergence improvement using the RCWA for crossed gratings", J. Opt. Soc. Am. A 24(9), 2880-2890 (2007) |
| [6] |
Bilski, B., Frenner, K., & Osten, W. (2011). About the influence of Line Edge Roughness on measured effective–CD. Optics Express, 19(21), 19967. doi:10.1364/OE.19.019967 |
| [7] | Bilski, B., Frenner, K., & Osten, W. (2012). Sensitivity analysis of line-edge roughness measured by means of scatterometry: a simulation-based investigation. Proceedings of SPIE, 8324, 83240J–83240J–9. doi:10.1117/12.916348 |
| [8] |
T. Schuster, S. Rafler, K. Frenner, W. Osten, “Influence of line edge roughness (LER) on angular resolved and on spectroscopic scatterometry”, Proc. SPIE 7155, 71550W (2008) |
| [9] |
Ferreras Paz, V., Schuster, T., Frenner, K., Osten, W., Szikszai, L., Mört, M., Hohle, C., et al. (2009). Simulation based sensitivity analysis and optimization of Scatterometry measurements for future semiconductor technology nodes. In W. Osten & M. Kujawinska (Eds.), Fringe 2009: 6th International Workshop on Advanced Optical Metrology (pp. 592–595). Springer Berlin Heidelberg. doi:10.1007/978-3-642-03051-2_101 |
| [10] |
Osten, W., Ferreras Paz, V., Frenner, K., Lyda, W., & Schau, P. (2011). Different approaches to overcome existing limits in optical micro- and nano-metrology. Proceedings of SPIE, 8011, 80116K–80116K–30. doi:10.1117/12.905277 |