Projection Optics with Free-Form Surfaces for Microlithography
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Solution Overview
Problem
Current projection optics for microlithography systems inadequately utilize refractive subunits, leading to suboptimal imaging performance and limited structural resolution due to the asymmetric and incomplete use of components.
Innovation Solution
Incorporation of static free-form surfaces in the projection optics, which cannot be described by a rotationally symmetrical function, allowing for more effective utilization of refractive components and enabling higher numerical apertures and improved imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional projection optics with rotationally symmetrical surfaces are used, then the design is simpler and easier to manufacture, but the utilization of refractive subunits is asymmetric and incomplete, leading to limited structural resolution
Solution Approach 1:
The patent applies asymmetry by replacing rotationally symmetrical optical surfaces with free-form surfaces that have no rotational symmetry. The free-form reflection surface and free-form refraction surface are specifically designed to asymmetrically direct light beams, enabling complete utilization of refractive subunits and achieving higher structural resolution in the image field.
Solution Approach 2:
The patent transitions from two-dimensional rotationally symmetrical surfaces to three-dimensional free-form surfaces with complex curvature variations in multiple directions. This dimensional complexity allows for independent control of light paths in different spatial dimensions, enabling superior imaging performance and resolution.
2Manufacturing precision
If more refractive components are used to increase image-side numerical aperture, then higher structural resolution is achieved, but the components are not effectively utilized due to asymmetric beam paths
Solution Approach 1:
The free-form surfaces create symmetric light propagation paths through asymmetric surface geometries, ensuring that light beams pass symmetrically through all refractive components in the subunits. This symmetric beam path enables effective utilization of every refractive component, maximizing component utilization efficiency while achieving high structural resolution.
3Adaptability or versatility
If static free-form surfaces are used, then degrees of freedom for guiding imaging light are increased and component utilization is improved, but the design and manufacturing complexity increases
Solution Approach 1:
The patent employs asymmetric free-form surfaces that provide maximum light guidance flexibility by independently controlling ray paths in all directions. These surfaces are designed with specific asymmetric curvature profiles that enable precise beam shaping and routing, achieving superior adaptability in guiding imaging light through the optical system.
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 use of static free-form surfaces increases the degrees of freedom for guiding imaging light, resulting in higher structural resolution and more efficient use of refractive components, enabling larger image-side numerical apertures and improved imaging performance.
Implementation Method 1
A reflection surface of the mirror is configured as a static free-form surface which cannot be described by a rotationally symmetrical function
Implementation Method 2
The use of at least one free-form surface can allow an imaging beam path in the at least one refractive subunit of the projection optics that utilises the components contained therein more effectively
Data Source
AI summary
A projection optics for microlithography, which images an object field in an object plane into an image field in an image plane, where the projection optics include at least one curved mirror and including at least one refractive subunit, as well as related systems, components, methods and products prepared by such methods, are disclosed.