Three-Mirror Relay Optics for Small Wafer Defect Inspection
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Solution Overview
Problem
Existing inspection tools are becoming less efficient and effective in detecting smaller defects due to advancements in large-scale circuit integration and size reduction.
Innovation Solution
An imaging objective with a three-mirror all-reflective relay system, featuring different curvatures, provides a diffraction-limited intermediate image, allowing for efficient defect detection and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inspection tools are used, then existing defect detection capability is maintained, but detection effectiveness deteriorates as defects become smaller
Solution Approach 1:
The patent employs three spherical mirrors with different curvatures in the relay optics to achieve diffraction-limited imaging performance. The curved reflective surfaces enable precise control of light paths and wavefronts, maintaining high measurement precision for detecting smaller defects while avoiding the limitations of conventional optical systems.
Solution Approach 2:
The patent replaces conventional lens-based optical systems with an all-reflective optical system using spherical mirrors. This substitution eliminates chromatic aberrations and reduces stray light issues inherent in refractive systems, thereby improving detection reliability for smaller defects through diffraction-limited performance.
2Adaptability or versatility
If all-reflective optical systems are used, then broadband inspection capability is achieved, but system complexity increases
Solution Approach 1:
The patent uses three spherical mirrors with specifically designed different curvatures to simplify the all-reflective optical system while maintaining broadband inspection capability. The spherical geometry provides inherent aberration correction properties that reduce system complexity compared to using aspherical or complex multi-element lens systems.
Solution Approach 2:
The all-reflective optical system with three spherical mirrors serves multiple functions: it provides broadband inspection capability, achieves diffraction-limited performance, and maintains a fixed image plane. This multi-functionality reduces the need for additional optical components, thereby managing system complexity while enhancing versatility.
3Measurement precision
If diffraction-limited intermediate image is produced, then imaging precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs spherical mirrors instead of aspherical mirrors, which are much easier to manufacture with high precision. The spherical geometry provides a good balance between achieving diffraction-limited imaging precision and maintaining feasible manufacturing precision requirements for the mirror surfaces.
Solution Approach 2:
The three spherical mirrors are positioned and configured with different curvatures to distribute the imaging requirements across multiple components. This allows each mirror to be manufactured with moderate precision while the combined system achieves diffraction-limited performance, reducing the burden on individual component manufacturing.
4Object-affected harmful factors
If three spherical mirrors with different curvatures are used, then aberrations and stray light are reduced, but device complexity increases
Solution Approach 1:
The patent replaces conventional lens-based relay optics with an all-reflective system using three spherical mirrors. This substitution inherently reduces chromatic aberrations and allows for better control of stray light through reflective surfaces, while the spherical geometry simplifies the overall system design compared to complex lens assemblies.
Solution Approach 2:
The use of three spherical mirrors with different curvatures provides effective aberration correction and stray light reduction. The spherical surfaces offer inherent symmetry and predictable optical paths that simplify the design process and reduce the need for additional corrective elements, thereby managing device complexity while achieving the desired reduction in harmful optical factors.
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 diffraction-limited performance, enabling confocal applications and reducing aberrations, stray light, and manufacturing costs while maintaining a fixed image plane for improved defect inspection efficiency.
Implementation Method 1
The relay includes three spherical mirrors positioned to deliver a projection of the intermediate image to a fixed image plane. The three spherical mirrors may be all reflective mirrors with substantially no obscuration
Implementation Method 2
a front objective configured to produce a diffraction limited intermediate image
Data Source
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AI summary
Imaging objectives and inspection systems equipped with such imaging objectives are disclosed. The imaging objective may include a front objective configured to produce a diffraction limited intermediate image. The imaging objective may also include a relay configured to receive the intermediate image produced by the front objective. The relay may include three spherical mirrors positioned to deliver a projection of the intermediate image to a fixed image plane.