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Designing multilayer mirror structures to achieve high pupil transmittance uniformity in EUV lithography
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DOI：10.1117/1.OE.65.4.045103.png)
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Abstract
En 中文
The purpose of this work is to develop design schemes for extreme ultraviolet (EUV) multilayer mirrors to deal with a large asymmetric distribution of angle of incidence (AOI) as posed by high numerical aperture (NA) EUV projection optics. A six-mirror projection optics with an NA of 0.26 has been considered to design multilayer mirrors by rigorous investigation of pupil transmittance uniformity. For mirror surfaces having rotational asymmetry and a large inter-field span in AOI (the second but last mirror surface), the conventional uniform and radially graded Mo/Si-based periodic thickness mirrors (PTM) are found to fail to achieve appreciable pupil uniformity. 2D distributed PTM design, which satisfies Bragg criteria pointwise, also fails to achieve pupil uniformity due to large inter-field span and rotational asymmetry in AOI. To cope with such a surface, an approach with a laterally graded and vertically aperiodic thin film structure has been developed. This method is capable of achieving high pupil transmittance uniformity (standard deviation similar to 1.95%) and average pupil transmittance (similar to 65.5%). The demonstrated method can also be applied to beyond extreme ultraviolet projection optics around 7 nm wavelength for next-generation semiconductor chip manufacturing technology.
Keywords:
EUV lithography
EUV mirror
bragg mirror
projection optics
pupil map
Journal
O
IF:
1.2
Papers:
178
Citations:
1.1W
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