Unit-Magnification Catadioptric Projection Systems for Large Rectangular Fields
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Solution Overview
Problem
Existing unit-magnification optical systems are limited in their ability to provide sharp imagery over large rectangular fields and extended working distances, making them unsuitable for applications such as masked laser-patterning of liquid crystal, LED, and OLED display panels, which require large rectangular exposure fields and working distances greater than 100 mm.
Innovation Solution
A large-field unit-magnification optical system design incorporating a concave and convex mirror with a positive lens spaced from the convex mirror, and optionally a second positive lens and plane mirrors to separate the image and object planes, ensuring symmetry relative to the aperture stop for intrinsic correction of coma and distortion, and adjustment of radii and aspheric coefficients to reduce remaining aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If concentric spherical mirrors are used to achieve unit magnification imaging, then the system is free of spherical aberration and intrinsically corrected for coma and distortion, but the field of view is restricted to a narrow annular area only
Solution Approach 1:
The optical system is divided into multiple reflective zones on the mirrors. The mirrors are segmented into a central zone and an annular zone, each contributing to different portions of the field of view. This segmentation allows the system to maintain aberration correction while expanding the usable field area beyond a narrow annulus.
Solution Approach 2:
The patent transitions from a two-dimensional narrow annular field to a three-dimensional volumetric field by utilizing multiple reflective zones at different radial positions on the mirrors. This dimensional expansion allows light rays from different field positions to be properly directed, achieving a large volumetric field of view while maintaining unit magnification and aberration correction.
2Manufacturing precision
If a narrow ring-field design is used with concentric mirrors, then sharp imagery is achieved over a narrow annular area, but the system cannot provide large rectangular exposure fields required for photolithography applications
Solution Approach 1:
The patent introduces asymmetric field curvatures in the x and y directions by carefully designing the mirror surfaces with different curvatures along orthogonal axes. This asymmetric design allows the system to correct for field curvature while maintaining a large rectangular field geometry, rather than being constrained to a circular or annular field shape.
Solution Approach 2:
The mirror surface parameters, particularly the radii of curvature and conic constants, are optimized to achieve both sharp imagery and large rectangular field coverage. By adjusting these parameters, the system transitions from producing only narrow annular fields to generating large rectangular exposure fields suitable for photolithography while maintaining diffraction-limited image quality.
3Length of moving object
If the object and image planes are separated by a large distance, then working distance greater than 100 mm is achieved, but existing unit-magnification systems cannot maintain sharp imagery over such extended distances
Solution Approach 1:
The optical system is designed with dynamic flexibility allowing the object and image planes to be positioned at various distances while maintaining unit magnification and sharp imagery. The multi-zone mirror configuration enables the system to accommodate working distances greater than 100 mm by properly directing light rays over these extended distances without introducing significant aberrations.
Solution Approach 2:
The patent creates a universal optical system that can function effectively across a wide range of working distances (greater than 100 mm) while maintaining unit magnification and diffraction-limited image quality. The system is not limited to a fixed working distance but can adapt to various object-image plane separations, making it suitable for different photolithography application requirements.
4Manufacturing precision
If symmetric catoptric systems with concentric mirrors are used, then coma and distortion are intrinsically corrected, but the system cannot provide extended spectral range correction without additional refractive elements
Solution Approach 1:
The reflective optical system inherently corrects for chromatic aberrations and provides extended spectral range capability without requiring additional refractive elements. The mirrors serve multiple functions: they provide the primary imaging function, correct for monochromatic aberrations through their specific surface configurations, and simultaneously correct for chromatic aberrations by reflecting all wavelengths equally. This self-service approach eliminates the need for separate achromatic lens assemblies.
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 design achieves diffraction-limited image quality over extended spectral ranges and large rectangular fields, enabling high-throughput masked laser-patterning applications with working distances greater than 100 mm and rectangular exposure fields longer than 100 mm, suitable for various illumination wavelengths.
Implementation Method 1
The mirrors are arranged to produce at least three reflections within the system
Implementation Method 2
A positive lens is spaced from the convex mirror on the opposite side of the concave mirror
Data Source
AI summary
Ring-field, catoptric and catadioptric, unit-magnification, projection optical systems having non-concentric optical surfaces are disclosed. Each system has a system axis with object and image planes on opposite sides of the system axis. The non-concentric surfaces allow for working distances of the object and image planes in excess of 100 millimeters to be achieved, with a ring-field width sufficient to allow a rectangular object-field having a long dimension in excess of 100 mm to be projected.