Pupil-Relay Optics for EUV Reticle Pupil Intensity Measurement
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Solution Overview
Problem
Conventional deep ultraviolet (DUV) inspection systems are inadequate for resolving features and defects in smaller node sizes, and extreme ultraviolet (EUV) inspection systems face challenges with beamsplitters that strongly absorb EUV wavelengths, leading to low reflection and transmission coefficients, which complicates the detection of pupil intensity profiles.
Innovation Solution
The implementation of imaging optics with an aperture stop, objective optics, and pupil-relay optics that can be configured between field-imaging and pupil-imaging modes, allowing for the detection of field and pupil images on a detector, and a method to compensate for relay-reflectivity profiles to determine the pupil-intensity profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If beamsplitters are used in EUV inspection systems to simplify optical design and enable pupil intensity profile measurement, then optical design is simplified and measurement capability is enabled, but light loss increases significantly due to low reflection and transmission coefficients (25-35%)
Solution Approach 1:
The patent removes the beamsplitter from the optical path entirely, extracting the problematic light-loss element while preserving the essential functionality through alternative means (direct imaging of the pupil plane using reflective optics)
Solution Approach 2:
The patent creates an optical copy or image of the pupil plane directly on the detector using reflective optics, eliminating the need for beamsplitter-based reference beam creation while maintaining measurement capability
2Ease of manufacture
If DUV inspection systems are used for mask inspection, then the systems are non-actinic and easier to implement, but the image resolution and contrast are insufficient for smaller node sizes
Solution Approach 1:
The patent changes the fundamental operating parameter from non-actinic DUV wavelengths to actinic EUV wavelengths (13.5 nm), transforming the inspection system's interaction with the mask to achieve the resolution and contrast needed for smaller node sizes while maintaining system feasibility
3Measurement precision
If EUV inspection systems use actinic radiation (13.5 nm) to resolve smaller node sizes, then measurement precision is improved, but beamsplitter implementation becomes difficult due to strong absorption
Solution Approach 1:
The patent extracts the beamsplitter component from the EUV inspection system, removing the source of complexity and light loss while maintaining the ability to perform pupil intensity profile measurements through direct imaging of the pupil plane
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
Enables accurate measurement of pupil intensity profiles and field images, enhancing the detection of defects in EUV masks by overcoming the limitations of DUV and EUV inspection systems, particularly in resolving smaller node sizes and improving defect detection capabilities.
Implementation Method 1
The objective optics include a first objective mirror, a second objective mirror, a third objective mirror, and a fourth objective mirror; and pupil-relay optics, wherein the pupil-relay optics include at least a first pupil-relay mirror
Data Source
AI summary
An inspection system may be an EUV reticle inspection tool. The inspection system may include objective optics and imaging optics. The imaging optics may include pupil-relay optics. A first pupil-relay mirror of the pupil-relay optics may be extended into and retracted from the imaging path to enable imaging field images and pupil images on a detector. The pupil images may be used for measuring the intensity profile in pupil. Configurations of the pupil-relay optics may include the first pupil-relay mirror extending between a second and third objective mirrors of the objective optics or extending between fourth objective mirror of the objective optics and the detector.