Projection Lens Wavefront Manipulator for Overlay Error Correction
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Solution Overview
Problem
Current microlithographic projection exposure methods face challenges in achieving high superimposition accuracy between successive exposure steps, leading to overlay errors that increase fabrication costs and reduce yield due to inadequate overlay precision.
Innovation Solution
A projection lens with a wavefront manipulation system that dynamically alters the wavefront of projection radiation using a manipulator surface with a reversible actuating device, allowing for targeted field-dependent distortion correction and improved superimposition accuracy by adjusting the optical path length changes across the image field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional projection lenses are used without wavefront manipulation, then the device complexity is low, but the superimposition accuracy between successive exposure steps deteriorates due to uncorrected field-dependent distortion
Solution Approach 1:
A wavefront manipulator is introduced as an intermediary optical element between the object plane and image plane. This manipulator includes a manipulator surface with variable optical path length that dynamically corrects field-dependent distortion in the projection radiation, thereby improving superimposition accuracy without requiring changes to the fundamental lens structure
Solution Approach 2:
The wavefront manipulator employs a variable optical path length between the object plane and manipulator surface, allowing dynamic adjustment of the correction effect. This enables the system to adapt to different exposure conditions and maintain optimal superimposition accuracy across varying operational parameters
2Measurement precision
If the numerical aperture NA is increased to improve resolution, then the resolution capability improves, but the field-dependent distortion increases leading to worse superimposition accuracy
Solution Approach 1:
The system changes the optical path length parameter dynamically across the field of view using the wavefront manipulator. By varying the optical path length as a function of field position, the system compensates for the increased field-dependent distortion that occurs at higher numerical apertures, thereby maintaining both high resolution and high superimposition accuracy
3Productivity
If multiple exposure steps are performed to achieve high integration density, then the productivity increases, but the overlay errors accumulate leading to worse manufacturing precision
Solution Approach 1:
The wavefront manipulator system incorporates feedback control to measure and correct field-dependent distortion in real-time during each exposure step. By continuously monitoring and adjusting the optical path length to compensate for distortion, the system prevents overlay error accumulation across multiple exposure steps, maintaining high manufacturing precision throughout the fabrication process
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 successive exposure steps, reducing overlay errors and improving the precision of fabricated structures, thereby increasing the yield and reducing fabrication costs.
Implementation Method 1
a wavefront manipulator for dynamically altering the wavefront of the projection radiation passing from the object plane to the image plane of the projection lens
Implementation Method 2
The first manipulator includes a first actuating device, which allows the surface shape and/or the refractive index distribution of the first manipulator surface to be altered reversibly
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 (OS) 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.