Polarized Oblique Defect Imaging for Minute Surface Inspection
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Solution Overview
Problem
Conventional defect inspection methods face challenges in achieving high-sensitivity detection of minute defects due to reduced light detection quantity and decreased resolution, particularly when the optical axis is inclined relative to the sensor surface, leading to defocusing and difficulty in optimizing antireflection film thickness.
Innovation Solution
A defect inspection apparatus with a polarization control unit that separates and rotates light by specific polarization directions, using a sensor unit with an array-shaped light receiving portion and antireflection film, and adjusting the optical axis and sensor arrangement angles to enhance light absorption and imaging resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical axis of the detection system is inclined to detect reflected light from the defect, then the quantity of light detected by the sensor decreases, but the resolution of the image formed on the sensor surface improves
Solution Approach 1:
The patent introduces polarization dimension to the optical detection system. By controlling the polarization state of incident and reflected light, the system can optimize both light collection efficiency and image resolution simultaneously, resolving the contradiction between detecting sufficient light and achieving high resolution under oblique illumination conditions
Solution Approach 2:
The patent changes the polarization parameter of light to resolve the contradiction. By adjusting polarization control units to match the polarization state of incident light with the optimal detection polarization state, the system maximizes light detection quantity while maintaining high image resolution through controlled oblique illumination geometry
2Quantity of substance
If the incident angle of light on the sensor surface is reduced to optimize antireflection film effectiveness, then light absorption efficiency improves, but the variation in incident angle increases making it difficult to optimize film thickness
Solution Approach 1:
The patent applies preliminary action by pre-optimizing the antireflection film thickness for the specific oblique incident angle range used in the inspection system. The film thickness is designed in advance to match the predetermined illumination geometry, ensuring high light absorption efficiency without requiring complex adaptive mechanisms
Solution Approach 2:
The patent makes the antireflection film design universal for the entire inspection field by carefully selecting the incident angle range and corresponding film thickness. This single optimized film design works effectively across all detection positions, eliminating the need for position-dependent film thickness variations
3Quantity of substance
If the imaging magnification is reduced to bring the incident angle closer to normal direction, then light absorption by the sensor improves, but the resolution decreases making it difficult to detect minute defects
Solution Approach 1:
The patent resolves this contradiction by introducing polarization control as an additional dimension. This allows the system to maintain high imaging magnification for resolution while using polarization-matched oblique illumination to ensure sufficient light absorption, eliminating the need to reduce magnification
Solution Approach 2:
The patent changes the polarization parameter to enable high magnification operation. By controlling polarization states to match between incident light and sensor response, the system achieves both high light absorption and high resolution simultaneously, avoiding the trade-off that would otherwise require magnification reduction
4Measurement precision
If oblique illumination is used to detect minute defects, then the quantity of illumination required increases, but the antireflection film effectiveness is compromised due to polarization characteristics
Solution Approach 1:
The patent changes the polarization parameter of the illumination light to match the optimal detection polarization state. This parameter optimization ensures that the antireflection film works effectively at oblique angles, maximizing light absorption efficiency and reducing the total quantity of illumination needed while maintaining high defect detection sensitivity
Solution Approach 2:
The patent implements feedback through polarization control units that adjust the polarization state of incident light based on the detected polarization characteristics of reflected light from defects. This feedback mechanism optimizes the illumination quantity by ensuring maximum light absorption efficiency through matched polarization states
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 and high-resolution imaging detection of minute defects, even with varying operation distances, by optimizing light absorption and reducing defocusing effects.
Implementation Method 1
a first wavelength plate that rotates a polarization direction of incident light
Implementation Method 2
a polarization beam splitter that separates light whose polarization direction is rotated by the first wavelength plate depending on the polarization direction
Implementation Method 3
an antireflection film at a position conjugate with the illumination spot with which the sample surface is irradiated
Data Source
AI summary
A defect inspection apparatus includes an illumination unit configured to irradiate a surface of a sample with a linear illumination spot; a condensing detection unit configured to condense reflected light of the illumination spot and to control a polarization state of the incident light to form an optical image; and a sensor unit configured to output the optical image and including an array-shaped light receiving portion and an antireflection film at a position conjugate with the illumination spot, in which the condensing detection unit includes a polarization control unit configured to increase light incident efficiency to the sensor unit. The normal line of the light receiving surface of the sensor unit is inclined from the optical axis of the condensing detection unit by 10 degrees or more and less than 80 degrees. The light condensing detection unit increases the optical magnification in the lateral direction of the illumination spot.