Asymmetric Lithography Mark Detection for Defocus Correction
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Solution Overview
Problem
Existing detection systems for aligning substrates and molds in imprint apparatuses suffer from defocus errors that affect the accuracy of relative position measurement between marks on the objects.
Innovation Solution
A detection device with an illumination system that forms asymmetric light intensity distributions and uses asymmetric or symmetric aperture stops to illuminate marks, combined with a processor that corrects for defocus based on correlation with defocus amounts, enabling high-accuracy relative position detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional detection system with symmetric illumination and aperture stop is used, then the system structure is simple, but defocus errors occur that reduce measurement precision
Solution Approach 1:
The patent applies asymmetry by configuring the illumination system to create an asymmetric light intensity distribution on the pupil surface, or by using an asymmetric aperture stop. This asymmetric configuration causes the imaging position to shift in response to defocus, enabling the system to detect and correct defocus errors. The asymmetric illumination pattern or aperture stop breaks the symmetry that would otherwise make the system insensitive to defocus, thereby improving measurement precision without requiring complex additional components.
2Measurement precision
If defocus is present in the detection system, then the alignment process is simpler, but the position detection accuracy deteriorates due to defocus errors
Solution Approach 1:
The patent implements feedback by using the asymmetric illumination or aperture stop to generate a signal that indicates the presence and magnitude of defocus. The image sensor detects the shifted imaging position caused by defocus, and this information is fed back to the alignment system. The processor uses this feedback to calculate correction values that compensate for the defocus error, thereby maintaining high detection accuracy throughout the alignment process without requiring manual intervention to adjust for defocus.
3Measurement precision
If symmetric illumination is used, then the illumination system is simpler, but the system cannot detect defocus amounts
Solution Approach 1:
The patent applies asymmetry to the illumination light distribution by configuring the illumination system to produce an asymmetric intensity pattern on the pupil surface. This asymmetric distribution is specifically designed so that when defocus occurs, the resulting image shift can be detected. The asymmetric illumination pattern acts as a probe that is sensitive to defocus, enabling the system to measure defocus amounts by detecting the direction and magnitude of the image position shift caused by the interaction between the asymmetric illumination and the optical system's defocus state.
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 allows for precise alignment of substrates and molds by accurately determining the relative position between marks, reducing measurement errors due to defocus and enhancing the overall alignment process.
Implementation Method 1
a first detection system including a first image sensor and a first aperture stop and configured to form images of diffracted lights from the first mark and the second mark illuminated with the first illumination light by the illumination system on an imaging surface of the first image sensor
Data Source
AI summary
Device detects a relative position between first and second marks arranged to be superimposed The device includes illumination system to illuminate the first and second marks with first illumination light, first detection system including first image sensor and first aperture stop and configured to form images of diffracted lights from the first and second marks illuminated with the first illumination light on the first image sensor via the first aperture stop, and processor to obtain the relative position between the first and second marks. The first illumination light forms first light intensity distribution asymmetric with respect to the optical axis of the illumination system on pupil surface of the illumination system, or the first aperture stop is asymmetric with respect to the optical axis of the first detection system.