EUV Imaging Objective with Radially Graded Multilayer Reflectors
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Solution Overview
Problem
Current EUV lithography systems face challenges such as image distortions due to spherical aberrations and astigmatism caused by non-paraxial rays, limited Bragg-reflecting areas, and increased complexity with multiple optical elements, which hinder efficient manufacturing of next-generation integrated circuits.
Innovation Solution
An adjustable EUV imaging apparatus with concentric spherical reflectors that satisfy the Bragg condition at each point, allowing for variable de-magnifications and Bragg angles, and enabling rotation of the ray pattern to optimize photon throughput and reduce imaging errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Schwarzschild objectives are used with non-paraxial rays, then image transfer is achieved, but severe image distortions occur due to spherical aberration and astigmatism
Solution Approach 1:
The patent applies local quality by making the d-spacing of the multilayer reflector vary radially from the optical axis, creating different local properties across the reflector surface. Specifically, the d-spacing increases from the center toward the edge, which compensates for the non-paraxial ray angles and eliminates spherical aberration and astigmatism while maintaining sharp images across the entire field of view.
Solution Approach 2:
The patent changes the physical parameter of d-spacing in the multilayer reflector structure to optimize performance for non-paraxial rays. By radially varying the d-spacing parameter, the system achieves corrected imaging for EUV lithography applications, transforming the conventional fixed d-spacing design into an optimized variable parameter structure that eliminates optical aberrations.
2Ease of manufacture
If the Bragg condition is satisfied only locally on reflectors, then manufacturing is simplified, but the Bragg-reflecting area is limited requiring multiple exposures
Solution Approach 1:
The patent applies local quality by making the d-spacing of the multilayer reflector vary radially from the optical axis, creating different local properties across the reflector surface. Specifically, the d-spacing increases from the center toward the edge, which compensates for the non-paraxial ray angles and eliminates spherical aberration and astigmatism while maintaining sharp images across the entire field of view.
Solution Approach 2:
The patent achieves multi-functionality by designing a single reflector structure that simultaneously satisfies the Bragg condition across its entire surface for all incident angles. The radial variation in d-spacing ensures that every point on the reflector contributes to the imaging process, enabling the entire object to be imaged in a single exposure rather than requiring multiple sequential exposures.
3Area of stationary object
If lateral grading of d-spacing is applied to increase Bragg-reflecting area, then reflecting area increases, but spherical symmetry is destroyed causing additional imaging errors
Solution Approach 1:
The patent applies local quality by making the d-spacing of the multilayer reflector vary radially from the optical axis, creating different local properties across the reflector surface. Specifically, the d-spacing increases from the center toward the edge, which compensates for the non-paraxial ray angles and eliminates spherical aberration and astigmatism while maintaining sharp images across the entire field of view.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables stigmatic imaging with increased photon throughput, reduced image distortions, and the ability to image entire objects in a single exposure, improving the manufacturing process for next-generation integrated circuits by maximizing Bragg reflecting areas and eliminating astigmatism.
Implementation Method 1
an objective wherein the Bragg condition is simultaneously fulfilled at each point on the surfaces of two spherical reflectors
Implementation Method 2
two spherical reflectors... each pair includes a convex reflector with a radius of curvature R1 and a Bragg angle θ1, and a concave reflector with a radius of curvature R2 and a Bragg angle θ2
Data Source
AI summary
Disclosed is an imaging apparatus for EUV spectroscopy, EUV microscopy, EUV lithography, and x-ray imaging. This new imaging apparatus could, in particular, make significant contributions to EUV lithography at wavelengths in the range from 10 to 15 nm, which is presently being developed for the manufacturing of the next-generation integrated circuits. The disclosure provides a novel adjustable imaging apparatus that allows for the production of stigmatic images in x-ray imaging, EUV imaging, and EUVL. The imaging apparatus of the present invention incorporates additional properties compared to previously described objectives. The use of a pair of spherical reflectors containing a concave and convex arrangement has been applied to a EUV imaging system to allow for the image and optics to all be placed on the same side of a vacuum chamber. Additionally, the two spherical reflector segments previously described have been replaced by two full spheres or, more precisely, two spherical annuli, so that the total photon throughput is largely increased. Finally, the range of permissible Bragg angles and possible magnifications of the objective has been largely increased.