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13 October 2011 EUV and x-ray scattering methods for CD and roughness measurement
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Abstract
Currently, scatterometry in semiconductor industry is performed in the visible and UV spectral ranges and is used to monitor process variations in production and development. The new challenge is to establish scatterometry as a traceable and absolute metrological method for dimensional measurements on semiconductor photomasks. In scatterometry, the properties of the photomasks structures are derived from an optimization which minimizes the difference between the measured scatter intensities and intensities calculated by numerical methods like FEM. We demonstrate that the inclusion of the roughness into the model provides simultaneously a better structure reconstruction and information on the structure roughness. The inclusion of the roughness is essential for the quality of the structure reconstruction from angular resolved scatterometry. Scattering with short wavelength radiation increases the sensitivity to structure details. Small angle X-ray scattering (SAXS) was already used in transmission mode for CD measurements at wafers. We used grazing incidence SAXS (GISAXS), i.e. the measurement of the scatter around the reflected X-ray beam in total reflection geometry for the characterization of EUV photomasks. We demonstrate the GISAXS diffraction pattern of periodic lines for large optical diffraction gratings to point out how generally structure parameters show up in these measurements. For absorber lines at an EUV test mask, the scatter figures became rather complex due to contributions from the various layers and surface structures of the mask. It is shown that GISAXS allows to derive geometrical properties and layer thicknesses for structured surface in a direct way without the need for numerical modelling. The information of SAXS can be used to complement EUV scatterometry. Particularly, it provides independent information on roughness and layer structures.
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Frank Scholze, Akiko Kato, Jan Wernecke, and Michael Krumrey "EUV and x-ray scattering methods for CD and roughness measurement", Proc. SPIE 8166, Photomask Technology 2011, 81661P (13 October 2011); https://doi.org/10.1117/12.896847
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