Defect Inspection Device Using Polarized Illumination
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Solution Overview
Problem
In optical defect inspection of substrates, bridge defects in high aspect ratio and short interval line and space patterns are difficult to detect due to challenges in illuminating and scattering light efficiently, especially with anisotropic shapes, and interference from surrounding patterns.
Innovation Solution
A defect inspection device and method using a combination of vertical and oblique illumination with polarization conversion to ensure illuminating light reaches bridge defects, enhancing scattered light detection by using a light source, objective lens, and detection optical systems with polarization filters to isolate and process scattered light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical inspection is used, then the inspection process is simple, but bridge defects in high aspect ratio and short interval L & S patterns cannot be detected
Solution Approach 1:
The inspection system is segmented into multiple independent illumination units (vertical illumination unit and oblique illumination unit) and multiple detection optical systems. Each unit can be independently controlled and optimized for specific defect types, allowing the complex inspection task to be divided into manageable segments that can be processed separately and combined for comprehensive defect detection
Solution Approach 2:
The patent introduces polarization dimension to the optical inspection system by incorporating polarization conversion units and polarization-selective optical filters. This adds a new dimension (polarization state) to the existing illumination and detection processes, enabling the system to distinguish bridge defects from background patterns through polarization contrast that is not available in conventional scalar optical inspection
2Measurement precision
If illuminating light is applied to bridge defects, then scattered light can be detected, but the L & S pattern causes noise that disables defect detection
Solution Approach 1:
The patent converts the harmful scattered light from the L & S pattern into a beneficial signal by using polarization modulation. The illumination units apply polarized light at specific angles, and the polarization conversion units modify the polarization state interactively with the pattern structures. This transforms the previously harmful diffuse scattering into polarized scattered light that carries both pattern information and defect information, which can then be separated using polarization-selective detection
Solution Approach 2:
The system dynamically changes illumination parameters (polarization angle, incident angle) and detection parameters (polarization filter orientation) to optimize the contrast between defect signal and pattern noise. By varying these parameters across multiple illumination and detection configurations, the system can enhance defect visibility while suppressing pattern-related noise through differential processing
3Measurement precision
If polarization conversion is applied, then scattered light from defects can be isolated, but the device complexity increases
Solution Approach 1:
The polarization conversion units are designed to perform multiple functions: they can convert linear polarization to circular polarization, modify polarization angles, and work in conjunction with oblique and vertical illumination modes. This multi-functionality reduces the need for separate specialized components for each illumination mode, thereby limiting the increase in overall device complexity while maintaining enhanced polarization control capabilities
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
Enables high-sensitivity detection of bridge defects by ensuring sufficient scattered light intensity and reducing noise from surrounding patterns, improving detection accuracy and efficiency.
Implementation Method 1
a polarization conversion unit that converts the laser emitted from the light source into linearly polarized light, and applies the laser passed through the polarization conversion unit to the line pattern formed on the sample, with the laser being set in a state polarized in a direction orthogonal to a longitudinal direction of the line pattern
Implementation Method 2
an optical filter that selectively transmitting a scattered light component from the defect on the sample having the line pattern by converting the polarization state of the reflected/scattered light entered and condensed by the objective lens into linear polarization
Implementation Method 3
an objective lens; a detection optical system unit which condenses and detects light that is reflected/scattered from the sample illuminated with the laser applied by the vertical illumination unit or the oblique illumination unit but that enters the objective lens
Implementation Method 4
a light source that emits laser
Implementation Method 5
having the defect cause the scattered light with high efficiency sometimes becomes difficult depending on the correlation between the polarization direction of the illuminating light reaching the defect position and the directional property of the defect
Data Source
AI summary
To detect a bridge defect between lines of a line pattern formed on a sample at pitches narrower than the wavelength of inspection light, a defect inspection device is configured to comprise: a light source which emits laser; a vertical illumination unit which applies the laser to the sample from a vertical direction via an objective lens by converting the laser into linearly polarized light by using a polarization conversion unit in a state polarized in a direction orthogonal to the longitudinal direction of the line pattern; an oblique illumination unit which applies the laser to the sample from an oblique direction; a detection optical unit including an optical filter which selectively transmits a scattered light component from the defect by converting the polarization state of the reflected/scattered light; and a signal processing unit which detects the defect on the sample by processing a detection signal.