Mathematical model for calculating speckle contrast through focus

Rene A. Claus; Andrew R. Neureuther; Patrick P. Naulleau

doi:10.1117/12.2012535

1 April 2013 Mathematical model for calculating speckle contrast through focus

Rene A. Claus, Andrew R. Neureuther, Patrick P. Naulleau

Proceedings Volume 8679, Extreme Ultraviolet (EUV) Lithography IV; 86791Y (2013) https://doi.org/10.1117/12.2012535
Event: SPIE Advanced Lithography, 2013, San Jose, California, United States

Abstract

The significantly reduced wavelength and the reflective nature of EUV masks causes phase variations resulting from roughness on the mask to result in intensity variations when the wafer is out of focus. These variations should be understood and modeled to control LER and device yield. A typical approach to modeling the effects of roughness is to image many masks using a thin mask simulator. These images can then be statistically analyzed to get the speckle properties. A model already exists that can relate speckle contrast to LER. This paper presents a method to compute the speckle image intensity using a single convolution with the roughness. This can be used to compute speckle through focus quickly. The presented technique takes into account defocus and the illumination coherence. It can be applied to phase roughness and amplitude roughness (reflectivity variations). In addition to speed improvements, the convolution kernel provides insights into the interaction of the source mask and mask roughness showing that, depending on the illumination coherence and defocus, not all roughness frequencies are attenuated equally.

Citation Download Citation

Rene A. Claus, Andrew R. Neureuther, and Patrick P. Naulleau "Mathematical model for calculating speckle contrast through focus", Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 86791Y (1 April 2013); https://doi.org/10.1117/12.2012535

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