IMPACT OF MODEL UNCERTAINTIES TO THE RECONSTRUCTION OF SURFACE PROFILES IN SCATTEROMETRY |
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| Hermann Gross, Andreas Rathsfeld, Frank Scholze, Markus Bär |
- Abstract:
- Scatterometry is a non-imaging indirect optical method in wafer metrology to characterize periodic surface structures with dimensions in the micro- and nanometer range. It is also important to lithography masks designed for extreme ultraviolet lithography (EUVL), where light with wavelengths in the range of 13 nm is applied. The solution of the inverse problem, i.e. the determination of periodic surface structures with respect to their critical dimensions (CD) and other profile properties from light diffraction patterns, is incomplete without knowledge of the uncertainties associated with the reconstructed parameters. With decreasing feature sizes of lithography masks, increasing demands on metrology techniques and their uncertainties arise. The numerical simulation of the diffraction process for periodic 2D structures can be realized by the finite element solution of the two-dimensional Helmholtz equation. The inverse problem can be formulated as a non-linear operator equation. The operator maps the sought mask parameters to the efficiencies of diffracted plane wave modes. The operator equation can be solved by optimization, i.e., minimizing the deviation of the calculated efficiency or phase shift values from the measured ones. Clearly, the uncertainties of the reconstructed profile parameters essentially depend on the uncertainties of the input data and can be estimated by various methods. A Monte Carlo procedure and an approximate covariance method is applied to evaluate the reconstruction algorithm. Particularly, we analyze the impact of uncertainties in the model parameters by the Monte Carlo method. Reconstruction results and their uncertainties are presented for the measurements of typical EUV masks. They are composed of 140 nm wide TaN absorber lines of about 80 nm height, a period of 420 nm, and with an underlying MoSi-multilayer stack of 49 periods.
- Keywords:
- scatterometry, inverse scattering, lithography masks
- Download:
- IMEKO-WC-2009-TC21-171.pdf
- DOI:
- -
- Event details
- Event name:
- XIX IMEKO World Congress
- Title:
Fundamental and Applied Metrology
- Place:
- Lisbon, PORTUGAL
- Time:
- 06 September 2009 - 11 September 2009