Catadioptric Projection Objective Chromatic Aberration Correction
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Solution Overview
Problem
Existing projection exposure apparatuses struggle to achieve demagnifying imaging of mask structures with minimal chromatic aberrations at operating wavelengths greater than 200 nm, while maintaining economic production with narrow quality tolerances, due to limited availability of suitable glasses for achromatization.
Innovation Solution
A catadioptric projection exposure apparatus is used, featuring a concave mirror and a negative lens group near the pupil, where the marginal ray height is greater than the chief ray height, allowing for effective chromatic correction without the need for different lens materials, primarily utilizing synthetic fused silica for all optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If refractive projection objectives are used at wavelengths ≤200 nm, then chromatic aberrations can be corrected using multiple lens materials, but the availability of suitable transparent materials is limited and production costs increase
Solution Approach 1:
The patent replaces the refractive lens system with a catadioptric system that uses a concave mirror for beam reflection. This substitution eliminates the need for multiple lens materials with different Abbe numbers, as the mirror provides chromatic correction without requiring scarce specialized glasses at wavelengths ≤200 nm
Solution Approach 2:
The projection objective combines different material types (refractive lenses and reflective mirrors) in a hybrid catadioptric design. This composite approach allows the system to achieve chromatic aberration correction through the reflective properties of the concave mirror while using readily available lens materials, reducing dependence on scarce specialized optical materials
2Manufacturing precision
If multiple lens materials with different Abbe numbers are used for chromatic correction, then chromatic aberrations are reduced, but the complexity of the optical system increases
Solution Approach 1:
The concave mirror in the catadioptric system replaces the need for multiple lens elements with different materials. The mirror's reflective surface provides the necessary optical power and chromatic correction without requiring complex multi-material lens assemblies, thereby reducing overall system complexity
Solution Approach 2:
The invention extracts the chromatic correction function from the refractive lens materials and transfers it to the reflective concave mirror. This separation allows the lens materials to be simpler and more readily available, while the mirror handles the chromatic aberration correction, simplifying the overall material selection process
3Ease of manufacture
If catadioptric projection objectives with concave mirrors are used, then material availability is improved, but chromatic aberrations are harder to correct compared to refractive systems
Solution Approach 1:
The catadioptric system combines refractive lenses with a reflective concave mirror in a hybrid configuration. This composite design allows the use of readily available lens materials while the mirror provides the necessary chromatic correction, achieving both material availability and optical performance
Solution Approach 2:
The concave mirror serves multiple functions: it provides the necessary optical power for the projection objective, enables beam folding for compact system design, and contributes to chromatic aberration correction. This multi-functionality allows the system to achieve chromatic correction without relying on scarce specialized lens materials
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
This approach enables high-resolution imaging with reduced chromatic aberrations, allowing for the production of semiconductor components with critical dimensions below 100 nm, while eliminating the dependence on scarce special glasses and simplifying material selection.
Implementation Method 1
catadioptric projection objectives, which in addition to a multiplicity of lenses also contain at least one concave mirror
Implementation Method 2
The negative lens near the pupil can provide a chromatic overcorrection that can at least partly compensate for the chromatic undercorrection of other objective parts
Data Source
AI summary
A projection exposure apparatus for the exposure of a radiation-sensitive substrate arranged in the region of an image surface of a projection objective with at least one image of a pattern of a mask that is arranged in the region of an object surface of the projection objective has a light source for emitting ultraviolet light from a wavelength band having a bandwidth Δλ>10 pm around a central operating wavelength λ>200 nm; an illumination system for receiving the light from the light source and for directing illumination radiation onto the pattern of the mask; and a projection objective for the imaging of the structure of the mask onto a light-sensitive substrate. The projection objective is a catadioptric projection objective having at least one concave mirror arranged in a region of a pupil surface of the projection objective, and a negative group having at least one negative lens arranged in direct proximity to the concave mirror in a region near the pupil surface, where a marginal ray height (MRH) of the imaging is greater than a chief ray height (CRH).