Oblique Illumination Defect Inspection with Adjustable Aperture
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Solution Overview
Problem
In optical dark-field defect inspection, vertical illumination is not effective for certain defect types, directions, or background patterns, leading to insufficient light reaching defects and reduced sensitivity in detection, especially when background patterns interfere with illumination and specular reflection is difficult to manage.
Innovation Solution
A defect inspection device with a light source, linear light condensing units, objective pupil optics, and a specular reflection light-blocking unit to control illumination and block specular reflection, allowing for sensitive defect detection by adjusting light-blocking widths and angles to optimize detection conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If vertical illumination is used for defect inspection, then the inspection setup is simple, but the illumination light is blocked by background patterns and cannot sufficiently reach defects, reducing detection sensitivity
Solution Approach 1:
Instead of using vertical illumination from above, the patent uses oblique illumination from the side, directing light at an angle to the sample surface. This inverted approach to illumination geometry allows light to reach defects that are obscured by background patterns in vertical illumination, thereby improving detection sensitivity without significantly increasing system complexity
Solution Approach 2:
The patent transitions from one-dimensional vertical illumination to two-dimensional oblique illumination by introducing an angular component. The illumination light is directed at a specific angle (e.g., 45 degrees) relative to the sample surface, creating a new dimensional approach that enables light to bypass background pattern obstructions and reach defects more effectively
2Object-affected harmful factors
If TTL illumination with a mirror is used to block specular reflection, then specular reflection is blocked, but the width of the light-blocking unit cannot be arbitrarily adjusted, preventing optimization of detection aperture conditions
Solution Approach 1:
The patent replaces the static mirror-based light-blocking unit with a dynamic adjustable aperture unit that can change its opening width. This aperture unit can be adjusted to different positions and sizes to optimize detection conditions for various defect types and illumination angles, providing flexibility that was not possible with fixed mirror configurations
Solution Approach 2:
The adjustable aperture unit serves multiple functions: it blocks specular reflection like the mirror, but also allows optimization of detection aperture conditions for different defect types, illumination angles, and inspection requirements. This multi-functional component replaces the single-function mirror while enhancing system versatility
3Measurement precision
If oblique illumination is used to improve defect detection, then detection sensitivity improves, but the illumination system becomes more complex
Solution Approach 1:
The patent introduces an objective pupil optical unit as an intermediary component that simplifies the oblique illumination system. This unit includes a pupil lens and aperture unit that work together to control and optimize the oblique illumination path, making the system more manageable and easier to adjust while maintaining the sensitivity benefits of oblique illumination
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 defects with various characteristics by ensuring sufficient illumination reaches the defects and effectively managing specular reflection, improving detection accuracy and reducing noise from background patterns.
Implementation Method 1
a first light-condensing unit that linearly condenses the laser beam emitted from the light source
Implementation Method 2
a second light-condensing unit that condenses light irradiated by the irradiation unit and generated from a sample
Implementation Method 3
a specular reflection light-blocking unit that blocks specular reflection light from the sample
Data Source
AI summary
A defect-inspection device includes an irradiation unit having an objective-pupil-optical unit that allows illumination light linearly condensed by a first light-condensing unit to pass through, and an objective lens that allows the illumination light having passed through the objective-pupil-optical unit to pass through; an irradiation-position-control unit that controls a passing position of the illumination light in the objective-pupil-optical unit disposed at a pupil surface of the objective lens; a detection unit having a second light-condensing unit that condenses light irradiated by the irradiation unit and generated from a sample, a specular-reflection light-blocking unit that blocks specular-reflection light from the sample and light components generated near the pupil surface among the light beams condensed by the second light-condensing unit, and an image-forming unit that images the light that is condensed by the second light-condensing unit and is not blocked by the specular-reflection light-blocking unit into a detector; and a defect-determination unit that detects a defect on a surface of the sample on the basis of a signal of the image imaged by the image-forming unit.