Focal Plane Image Splitting for Optical Inspection Uniformity
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Solution Overview
Problem
Existing optical inspection systems face challenges in increasing inspection speed and maintaining image quality when splitting images, as splitting before the focal plane leads to intensity reduction and non-uniformity, and existing methods like beam splitters result in light loss and altered angular distribution.
Innovation Solution
The image is split using beam splitters or lenses positioned at or within the focal plane, allowing for reduced non-uniformities and light loss by directing different portions of the image to multiple detectors, which act as an optically continuous surface, preserving angular distribution and intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If image splitting is performed before the focal plane using mirrors, then the field of view is enlarged, but intensity reduction and non-uniformity occur
Solution Approach 1:
A beam splitter is introduced as an intermediary optical element to divide the image into multiple portions for simultaneous detection. The beam splitter is positioned at the focal plane to ensure uniform intensity distribution across all detector portions, eliminating the non-uniformity problem caused by mirror-based splitting before the focal plane.
Solution Approach 2:
The patent transitions from a single detector to multiple detectors arranged in different spatial dimensions, allowing simultaneous capture of different image portions. This dimensional expansion enables enlarged field of view while maintaining intensity uniformity through proper beam splitter positioning at the focal plane.
2Productivity
If beam splitters are used to split the image, then the image can be divided for multiple detectors, but light loss occurs due to reflection
Solution Approach 1:
The patent optimizes the beam splitter parameters, specifically positioning it at the focal plane where the light distribution is most uniform. This parameter change minimizes the reflective losses while maintaining effective image splitting for parallel detection, thereby improving inspection speed without excessive light loss.
Solution Approach 2:
The beam splitter is designed to transmit a sufficient portion of light (more than the minimum 50% theoretical reflection) to the detectors by optimizing its orientation and position at the focal plane. This partial action approach ensures adequate light intensity reaches the detectors while still achieving effective image splitting for enhanced inspection productivity.
3Productivity
If multiple detectors are used to increase field of view, then inspection speed increases, but device complexity increases
Solution Approach 1:
The imaging system is segmented into multiple detection channels, each handling a specific portion of the image. This segmentation allows parallel processing of different image regions, significantly increasing inspection speed. The complexity is managed by using a beam splitter to naturally divide the optical path into distinct segments that can be processed independently.
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
This approach enhances inspection speed and accuracy by maintaining image quality and reducing light loss, while avoiding the issues of intensity reduction and non-uniformity associated with traditional splitting methods.
Implementation Method 1
The array of components may be configured to rotate the polarization of light entering the components. The components may be positioned so that the difference between rotation angles imparted by a pair of adjacent components in the array is ninety degrees.
Implementation Method 2
When using beam splitters, some of the rays (usually 50%) are reflected from the beam splitter while the rest of the rays are transmitted.
Implementation Method 3
Another embodiment provides that the array of components comprises an array of lenses. The lens array may be positioned so that light from a first portion of the image is focused by a first lens in the array to a first detector, and light from a second portion of the image is focused by a second lens in the array to a second detector.
Data Source
AI summary
In an optical inspection tool, an image of an object under inspection, such as a semiconductor wafer, may be obtained using imaging optics defining a focal plane. Light comprising the image can be split into portions that are detected using multiple detectors which each register a portion of the image. The image of the object at the focal plane can be split into two, three, or more parts by polarization-based beam splitters and/or lenses positioned tangent to the focal plane. The splitting apparatus may comprise a pair of arrays of half-cylinder lenses comprising a convex side and a flat side. The arrays can be positioned with the cylinder axes perpendicular to one another and the flat sides facing each other. Thus, the pair of arrays can divide incoming light into a plurality of rectangular portions without introducing non-uniformities which would occur if several spherical lenses are configured for use in a rectangular array.