Defect Inspection Device Using Polarization Separation for Signal Noise
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Solution Overview
Problem
Existing defect inspection technologies face challenges in accurately detecting fine defects on semiconductor substrates due to the weakness of scattered light from defects being mixed with background scattered light, making it difficult to separate the defect signal from the background noise, especially when the defects are smaller than 20 nm in size.
Innovation Solution
A defect inspection method and device that adjusts the polarization state and intensity distribution of laser light to irradiate the sample at an inclined angle, using a condensing lens to collect scattered light and separate it based on polarization direction, allowing for precise detection and processing of defect signals to distinguish between noise and defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarized light detection is performed to enhance defect signal, then defect detection sensitivity is improved, but it becomes difficult to separate defect signal from background scattered light in principle
Solution Approach 1:
The patent transitions from conventional single-point detection to three-dimensional angular detection. By arranging detectors at multiple angles (including oblique angles) relative to the sample surface, the system captures scattered light from defects in three-dimensional space. This dimensional expansion enables separation of defect signals from background scattered light through angular discrimination, resolving the contradiction between detection sensitivity and signal separation capability.
Solution Approach 2:
The patent segments the detection space into multiple angular zones by positioning multiple detectors at different angles. Each detector captures scattered light from specific angular regions, allowing the system to distinguish defect signals (which scatter at specific angles) from background scattered light (which has different angular distribution). This spatial segmentation resolves the signal separation issue while maintaining high detection sensitivity.
2Loss of information
If spatial filter is used to filter background scattered light, then background light reduction is achieved, but detection region is widened and hinders defect signal detection
Solution Approach 1:
Instead of using spatial filters that block light in the image plane, the patent employs angular filtering by positioning detectors at specific three-dimensional angles. This approach filters background scattered light based on its angular distribution characteristics without requiring physical masks that would reduce the detection area. The angular dimension provides selective background rejection while preserving full access to the sample surface.
3Illumination intensity
If oblique polarized illumination is used to enhance defect scattered light intensity, then defect signal intensity is improved, but polarization directions of background scattered light and defect scattered light change depending on emission direction
Solution Approach 1:
The patent segments the detection into multiple angular channels, each with optimized polarization analysis. Rather than attempting to analyze all scattered light at once with complex polarization optics, the system divides detection into discrete angular zones where polarization characteristics are more predictable and can be processed independently. This segmentation simplifies the overall polarization analysis while maintaining enhanced defect signal detection.
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 enables accurate detection and measurement of fine defects, providing stable inspection results while reducing heat damage to the sample and allowing for rapid scanning of the entire surface, improving the signal-to-noise ratio and enhancing defect detection sensitivity.
Implementation Method 1
condensing scattered light beams generated from the sample that has been irradiated with the shaped laser light
Implementation Method 2
adjusting a polarization direction of the scattered light beams that have been condensed by the condensing lens, mutually separating the scattered light beams of which the polarization directions have been adjusted depending on the polarization direction
Implementation Method 3
scattered light generated from the fine defect is very weakened, becomes difficult to discriminate between the scattered light generated from the defect and background scattered light
Data Source
AI summary
A defect inspection method includes irradiating a sample with laser, condensing and detecting scattered light beams, processing signals that detectors have detected and extracting a defect on a sample surface, and outputting information on the extracted defect. Detection of the scattered light beams is performed by condensing the scattered light beams, adjusting polarization directions of the condensed scattered light beams, mutually separating the light beams depending on the polarization direction, and detecting the light beams by a plurality of detectors. Extraction of the defect is performed by processing output signals from the detectors by multiplying each detection signal by a gain, discriminating between a noise and the defect, and detecting the defect.