|
The optical train is a key element of each lithography scanner. The single patterning resolution limit of a scanner is determined by the characteristics and performance of its imaging system consisting of illumination and projection optics. The most relevant performance parameters of the illumination system are the maximum achievable setting flexibility, off-axis imaging capability (sigma) and pupil fill ratio (PFR). The key drivers of the projection optics are numerical aperture (NA), aberration level, and stray light.
In this paper, we present an overview of the current EUVL generation and the optical system, designed to improve resolution limit, contrast and overlay performance within the scanner. The projection optics features a NA of 0.33 with significantly reduced aberration levels. These key scanner parameters have been substantially reduced to improve overlay and image contrast supporting volume production.
While double patterning is a possible extension with the current generation of EUVL tools, there is still a strong desire to print smaller chip patterns directly. Therefore a next generation of EUV called “High-NA EUV” is already in preparation. This tool generation with an optical system -ZEISS Starlith®5000- will have a NA of 0.55 and a resolution of 8nm for direct printing of these finest features. Achieving 8nm resolution means tighter specifications for the wavefront. Therefore, extreme aspheres with improved accuracy of the mirror surface are needed that pose next to the large size of the mirrors and the anamorphic design another challenge to the optics manufacturing. To build these systems a completely new production infrastructure is needed which is under installation in parallel with the product design and technology development. In this paper the current progress of the development will be shown.
|
