Faraday Rotator Positioning for Optical Inspection Systems
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Solution Overview
Problem
In semiconductor manufacturing, the use of Faraday rotators in reflective optical illumination systems leads to a significant reduction in light intensity, compromising inspection accuracy and increasing inspection time, while also generating a strong magnetic field that can affect adjacent elements, particularly the polarizing beam splitter.
Innovation Solution
The Faraday rotator is positioned between the polarizing beam splitter and the target, with a Faraday rotation angle within a specific range (−0.5 to 0.5 degrees), minimizing its influence on adjacent elements and optimizing light transmission to maintain sufficient light intensity for accurate inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Faraday rotator is used in a reflective optical illumination system to maintain polarization, then the light intensity is reduced to one-quarter of the original, but the inspection accuracy and time are improved
Solution Approach 1:
A λ/4 plate is introduced as an intermediary optical element between the light source and the mask. This plate converts linearly polarized light to circularly polarized light before reflection, and converts the reflected circularly polarized light back to linearly polarized light with preserved intensity, thereby mediating between the polarization maintenance requirement and the light intensity constraint
Solution Approach 2:
The patent changes the polarization state parameter of the light from linear to circular using the λ/4 plate, which fundamentally alters how the light interacts with the reflective mask surface. This parameter change enables the system to maintain both high light intensity and proper polarization control, resolving the intensity loss problem
2Productivity
If a Faraday rotator is positioned close to the polarizing beam splitter to control Faraday rotation, then the light transmission is optimized, but the magnetic field generated by the Faraday rotator affects adjacent optical elements
Solution Approach 1:
The patent eliminates the harmful magnetic field effect by replacing the Faraday rotator with a λ/4 plate that uses optical birefringence instead of magnetic fields. The λ/4 plate achieves the same polarization control function without generating magnetic interference, thereby converting the harmful magnetic field problem into a beneficial field-free optical solution
Solution Approach 2:
The patent substitutes the magneto-optic Faraday rotator system with an all-optical λ/4 plate system. This replacement eliminates the need for magnetic fields and electrical current in the optical path, substituting a purely optical mechanism that avoids magnetic interference with adjacent elements
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 configuration minimizes the degradation of light intensity and reduces the Faraday rotation effect on adjacent optical elements, enabling high-accuracy inspection of fine patterns on semiconductor masks and templates with reduced inspection time.
Implementation Method 1
a polarizing beam splitter configured to illuminate a target with light from the light source
Implementation Method 2
a sensor configured to capture an image of the inspection target by incidence of light reflected from the target
Implementation Method 3
a Faraday rotator provided between the polarizing beam splitter and the target
Data Source
AI summary
An imaging capturing apparatus comprising, a light source, a polarizing beam splitter configured to illuminate a target with light from the light source, a sensor configured to capture an image of the inspection target by incidence of light reflected from the target through the polarizing beam splitter, and a Faraday rotator provided between the polarizing beam splitter and the target and disposed away from the polarizing beam splitter such that a Faraday rotation angle in the polarizing beam splitter is within a range of an angle equal to or larger than -0.5 degrees and an angle equal to or smaller than 0.5 degrees.