Faraday Rotator Polarization Control for Mask Inspection Light Loss
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Solution Overview
Problem
In semiconductor manufacturing, the reflected illumination optical system used for mask inspection experiences significant light degradation, leading to reduced inspection accuracy and longer inspection times due to the halving of light quantity at each reflection, making it challenging to detect fine defects in mask patterns.
Innovation Solution
An image capturing device is designed with a polarization beamsplitter, Faraday rotator, and half-wavelength plate to minimize light degradation by rotating the polarization plane of light and optimizing the magnetic field or optical material thickness, allowing for higher light transmission and improved defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reflected illumination optical system is used for mask inspection, then the inspection can be performed with a straightforward optical path, but the light quantity degrades significantly (reduced to one-quarter of the original) due to multiple reflections, leading to reduced inspection accuracy and longer inspection times
Solution Approach 1:
The invention changes the polarization state parameter of light through a Faraday rotator and half-wavelength plate to achieve 90-degree polarization rotation. This allows the optical system to transmit light efficiently while maintaining the reflected illumination configuration, thereby improving light quantity and inspection accuracy without altering the basic optical path structure
Solution Approach 2:
The invention introduces a polarization control system (Faraday rotator and half-wavelength plate) as an intermediary between the light source and the mask. This intermediary component enables the light to maintain sufficient intensity after reflection by optimizing its polarization state, thus resolving the contradiction between ease of operation and measurement precision
2Device complexity
If a reflected illumination optical system is used for mask inspection, then the optical path can be simplified, but the inspection time increases due to insufficient light quantity requiring longer exposure
Solution Approach 1:
By changing the polarization parameters of light using the Faraday rotator and half-wavelength plate, the system maximizes light transmission efficiency. This allows the simplified optical structure to maintain high light quantity, thereby reducing inspection time and improving productivity without increasing device complexity
Solution Approach 2:
The polarization control system ensures continuous and efficient light transmission through the optical path by optimizing the polarization state at each stage. This maintains sufficient light quantity throughout the inspection process, enabling faster inspection speeds while keeping the optical system structure simple
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 enables high-accuracy inspection with minimal light degradation, allowing for the detection of fine defects in mask patterns without the need for a half mirror, thereby improving inspection efficiency and accuracy.
Implementation Method 1
a Faraday rotator having an optical material 1004a configured to rotate a polarization plane of light reflected from the polarization beamsplitter by changing intensity of a magnetic field or changing the thickness of the optical material
Data Source
AI summary
An image capturing device comprising, a light source configured to emit light having a predetermined wavelength, a polarization beamsplitter configured to receive the light from the light source, a Faraday rotator configured to rotate a polarization plane of the light via the polarization beamsplitter by changing the intensity of the magnetic field, an objective lens configured to illuminate an inspection target with the light transmitted through the Faraday rotator and a sensor configured to capture an optical image of the inspection target by causing the light reflected by the inspection target to be incident through the objective lens, the Faraday rotator, and the polarization beamsplitter.