Scheimpflug Catoptric Optics for Unobscured EUV Reticle Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
EUVL and EUV reticle inspection tools face challenges in achieving high magnification and resolution due to obscuration issues in mirror-based optical systems, which hinder the detection of defects in reflective reticles used in EUV lithography.
Innovation Solution
A catoptric system utilizing Scheimpflug optics and non-concentric optics is employed to generate high magnification images without obscuration, using a combination of concave mirrors configured to redirect light beams along oblique angles, followed by non-concentric optics to normalize the image plane, ensuring high intensity and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mirror-based optical systems are used in EUVL inspection tools, then the system can achieve high magnification, but obscuration occurs that degrades image intensity and resolution
Solution Approach 1:
The patent introduces oblique angles into the optical path configuration, transitioning from conventional normal-incidence optics to Scheimpflug optics that operate at non-zero angles. This dimensional change in the optical path geometry allows the system to achieve high magnification while avoiding obscuration, as the oblique angle configuration enables light to pass around obstructing elements rather than being blocked by them.
Solution Approach 2:
The patent changes the optical parameters by introducing oblique angles (non-zero incidence angles) into the optical path. By adjusting these angular parameters, the system achieves both high magnification and high resolution simultaneously, overcoming the traditional trade-off where increasing magnification would cause obscuration and degrade image quality.
2Object-generated harmful factors
If Scheimpflug optics are used to achieve high magnification without obscuration, then image intensity and resolution improve, but the image plane becomes oblique requiring additional non-concentric optics
Solution Approach 1:
The patent introduces non-concentric optics as an intermediary component that mediates between the Scheimpflug optics and the final image sensor. This intermediary system normalizes the oblique image plane produced by Scheimpflug optics into a conventional planar image that can be properly captured by standard sensors, thereby completing the optical path while maintaining the benefits of obscuration-free high-magnification imaging.
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 system achieves unobscured, highly magnified images with significantly improved resolution, enhancing the ability to detect and correct defects in EUV reticles, thereby improving the efficiency and effectiveness of EUV reticle inspection tools.
Implementation Method 1
Scheimpflug optics include two or more mirrors collectively configured and arranged in accordance with the Scheimpflug condition to collect the patterned light beams sourced from the imaged area and to redirect the light beams along a first optical axis such that the redirected light beams form an intermediate image at an intermediate image plane that is oblique to the object plane
Implementation Method 2
non-concentric optics includes two or more additional mirrors that are configured and arranged to correct the oblique light beam problem by normalizing the image plane (i.e., redirecting the light beams from the first optical axis to a second optical axis that is normal/perpendicular to the intermediate image plane)
Data Source
AI summary
A catoptric (mirror-based) optical system uses Scheimpflug optics and non-concentric optics to generate unobscured highly magnified images (e.g., >100×) in EUV reticle inspection tools. The Scheimpflug optics collect light beams from an object plane and directs the light beams along a first optical axis to generate an intermediate image at an intermediate image plane that is oblique to the object plane. The non-concentric optics redirect the light beams from the first optical axis to a second optical axis that is perpendicular to the intermediate image plane and generates a magnified image on a final image plane that is parallel to the intermediate image plane. The Scheimpflug optics may include a first mirror positioned to collect light beams reflected normal to the object plane and a second mirror positioned adjacent to the normal direction and configured to redirect the light beams onto the first optical axis.