Aberration control and characterization in a state of the art photolithographic lens have the tightest tolerances of any optical system. This is especially true in next generation extreme ultraviolet lithography systems with estimates for the wavefront tolerance below 500 pm RMS. These systems use radiation at a wavelength of 13.5 nm. No materials sufficiently refract this radiation, so reflective lens designs must be used. The mirrors are constructed as Bragg reflectors and much of the intense power of the source is ultimately distributed through the system as heat with each reflection. Moreover, the angle dependent reflection of these mirrors can also lead to amplitude asymmetries across the pupil. While interferometric techniques are the de-facto standard of wavefront analysis, they require the use of additional optics and are therefore difficult to implement during system use. Moreover, interferometric techniques cannot measure amplitude pupil variation.
In this work both the pupil amplitude and phase variation of several EUV lithography systems will be measured using images of binary targets formed by each system. Using the systems’ own images to monitor its wavefront has the benefit of providing an aberration monitor during system use. Models will be constructed between wavefront variation and a space-domain basis in which the effects of aberrations are separable. This allows both the amplitude and pupil variation to be rapidly extracted from these systems. Finally, the theory of anamorphic primary aberrations will be developed and the image-based method will be extended to these types of systems.
Microsystems Engineering (Ph.D.)
Department, Program, or Center
Microsystems Engineering (KGCOE)
Bruce W. Smith
Levinson, Zachary A., "Measurement of Amplitude and Phase Pupil Variation for EUV Lithography Systems" (2018). Thesis. Rochester Institute of Technology. Accessed from
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