Wafer Defect Inspection Imaging Objective with Spherical Mirror Relay
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Solution Overview
Problem
Existing inspection tools for semiconductor devices become less efficient in detecting smaller defects due to recent advancements in large-scale circuit integration and size reduction, necessitating improved inspection systems.
Innovation Solution
An imaging objective with a front objective configured to produce a diffraction-limited intermediate image and a three-spherical mirror relay, which delivers the image to a fixed location, providing a cost-effective and efficient solution for defect detection in semiconductor wafers and other polished plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inspection tools are used, then manufacturing cost is lower, but detection precision deteriorates for smaller defects
Solution Approach 1:
The imaging objective is segmented into two distinct parts: a front objective that produces a diffraction-limited intermediate image, and a relay system with three spherical mirrors that delivers this intermediate image to the detector. This segmentation allows each component to be optimized independently - the front objective for achieving diffraction-limited performance and the relay for cost-effective image delivery - thereby resolving the contradiction between precision and complexity.
Solution Approach 2:
An intermediate image is introduced as a mediator between the object plane and the detector. The front objective creates this intermediate image with diffraction-limited performance, which then serves as the input for the relay system. This intermediary approach enables the system to achieve high precision without requiring the entire optical path to be complex, as only the critical imaging function needs to be diffraction-limited.
2Manufacturing precision
If refractive optics are used, then manufacturing precision can be achieved, but lens heating and stray light increase
Solution Approach 1:
The patent replaces refractive optical elements (lenses) with reflective optical elements (spherical mirrors) in the relay system. This substitution eliminates lens heating and stray light issues inherent to refractive optics, while maintaining the ability to achieve diffraction-limited performance through the front objective. The reflective relay system provides a clean optical path without the harmful effects of glass absorption and scattering.
Solution Approach 2:
The patent changes the optical parameter from refractive index-based focusing (lenses) to reflective geometry-based focusing (spherical mirrors). By using mirrors with specific curvatures and positions, the system achieves the same imaging function without the thermal and stray light problems of refractive optics. This parameter change fundamentally alters how the optical system manages heat and stray light.
3Measurement precision
If high numerical aperture is used, then detection precision improves, but manufacturing cost increases
Solution Approach 1:
The optical system is segmented such that only the front objective requires high precision for diffraction-limited performance, while the relay system can use lower-cost spherical mirrors. This segmentation allows the system to achieve high detection precision without requiring all optical components to be expensive high-precision elements, thereby resolving the contradiction between precision and manufacturing cost.
Solution Approach 2:
The relay system with spherical mirrors creates an optical copy of the intermediate image at the detector plane. This copying process allows the system to achieve the necessary image quality without requiring the entire optical path to maintain high numerical aperture, as the spherical mirrors can replicate the image with lower manufacturing complexity and cost.
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 enables diffraction-limited performance, allowing for confocal applications, reducing aberrations, lens heating, and stray light, while maintaining a low manufacturing cost due to the all-reflective design and reduced numerical aperture, thereby enhancing the efficiency of defect inspection systems.
Implementation Method 1
a front objective configured to produce a diffraction limited intermediate image
Implementation Method 2
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 the detector
Data Source
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.