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22 March 2010 Identification, modeling, and observation of disturbing effects in EUV interferometer lithography
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The challenge of the Integrated Circuit size reducing leads to the development of new processes for future years. In the lithography domain, since several years, the EUV Lithography appears as a possible technique to reach the ITRS roadmap requirements. The EUV interferometry Lithography is still nowadays an efficient way to study and improve the EUV resist behaviors. Although the interferometer principle seems to be obvious, the optimization of its use is only reached regarding some huge constraints. In this work accurate numerical models and experimental studies have been developped. It shows that some undesirable effects can reduce the interference region and disturb the contrast of the resist printed lines. The EUV light is identified as the first issue. The beam divergence of EUV light affects the contrast quality of the fringes. The photometry computation, taking into account the optimum angular source light width is then detailed. The second cause is the Fresnel diffraction of light due to boundaries of the grating windows. Its superimposition with diffraction orders induces a damage of local printed interferences. This phenomenon leads to an edge disturbance of the interference fringes. The third cause addressed is the decrease of the interference area by the position of the wafer out of the focal distance. Possible shadowing effects are also shown.
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M. Saib, M. Besacier, C. Constancias, and P. Michallon "Identification, modeling, and observation of disturbing effects in EUV interferometer lithography", Proc. SPIE 7636, Extreme Ultraviolet (EUV) Lithography, 763628 (22 March 2010);

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