Projection Lens Wavefront Manipulator for Overlay Accuracy
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Solution Overview
Problem
Current projection lenses for microlithography face challenges in achieving high superimposition accuracy between successive exposure steps, leading to inadequate overlay and increased fabrication costs due to insufficient correction of aberrations and distortion in the imaging process.
Innovation Solution
A projection lens with a wavefront manipulation system that dynamically influences the wavefront of electromagnetic radiation by using a manipulator with a reversible surface shape and refractive index distribution, allowing for targeted correction of field-dependent distortion and aberrations, thereby improving overlay accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional projection lenses are used for microlithography, then the imaging process can be performed, but superimposition accuracy between successive exposure steps is insufficient leading to inadequate overlay
Solution Approach 1:
The projection lens is divided into multiple lens groups (first lens group, second lens group, third lens group) with distinct functions. The first lens group handles initial imaging, the second lens group provides distortion correction, and the third lens group performs final focusing. This segmentation allows each group to be optimized for specific tasks, improving overall overlay accuracy without requiring complete redesign of the entire lens system.
Solution Approach 2:
The patent employs variable focus lenses within the lens groups that can dynamically adjust their focal lengths during the imaging process. This dynamic adjustment capability allows the lens to compensate for field-dependent distortion and maintain high overlay accuracy across different field positions and exposure conditions, resolving the contradiction between maintaining simple structure and achieving precision.
2Device complexity
If the projection lens structure is simplified, then device complexity is reduced, but field-dependent distortion and aberrations are not sufficiently corrected
Solution Approach 1:
The second lens group is designed with multi-functional elements that simultaneously perform distortion correction, aberration reduction, and imaging tasks. By making this lens group universal in its capabilities, the patent achieves comprehensive distortion correction without adding separate dedicated correction components, thus maintaining relatively simple overall structure while improving manufacturing precision.
Solution Approach 2:
The patent utilizes lens elements with variable optical parameters (focal length, refractive index) that can be adjusted during operation. By changing these parameters dynamically, the lens system can adapt to different field positions and exposure conditions, providing effective distortion correction across the entire field without requiring a complex fixed-structure design.
3Manufacturing precision
If multiple lens groups are added to improve overlay accuracy, then manufacturing precision increases, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple functional requirements into integrated lens groups. For example, the second lens group simultaneously performs distortion correction, aberration control, and imaging functions that could otherwise require separate components. This merging approach achieves high superimposition accuracy while limiting the increase in device complexity and cost.
Solution Approach 2:
Different lens groups are designed with locally optimized properties tailored to their specific functions. The first lens group is optimized for initial imaging, the second for distortion correction with specific optical characteristics, and the third for final focusing. This local quality optimization allows each group to perform its function efficiently, achieving high overall precision without requiring all groups to be equally complex.
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 enhances superimposition accuracy between exposure steps, reducing overlay errors and fabrication costs by enabling precise field-dependent distortion correction without introducing significant additional aberrations.
Implementation Method 1
a wavefront manipulation system for dynamically influencing the wavefront of the projection radiation passing from the object plane to the image plane of the projection lens
Implementation Method 2
altering the surface shape and/or refractive index distribution of the first manipulator surface
Implementation Method 3
transparent refractive optical elements having refractive power (lens elements)
Implementation Method 4
reflective elements having refractive power, that is to say curved mirrors. Typically, at least one concave mirror is contained
Data Source
AI summary
A projection lens for imaging a pattern arranged in an object plane of the projection lens into an image plane of the projection lens via electromagnetic radiation having an operating wavelength λ<260 nm has a multiplicity of optical elements having optical surfaces which are arranged in a projection beam path between the object plane and the image plane. Provision is made of a wavefront manipulation system for dynamically influencing the wavefront of the projection radiation passing from the object plane to the image plane.