Oblique Illumination Lens Unit for Substrate Defect Detection
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Solution Overview
Problem
Conventional optical inspection tools face limitations in enhancing resolution for detecting surface defects on substrates, particularly with oblique illumination, due to physical constraints such as focal distance and lens diameter, which hinder precise imaging of groove-shaped defects and other surface irregularities.
Innovation Solution
The optical inspection tool incorporates a lens unit with at least a pair of beam paths that allow for oblique illumination, featuring empty spaces or flat regions within the lenses to accommodate increased lens diameter and reduced focal distance, enabling precise positioning of the substrate and enhanced image resolution through auxiliary light sources and sensing units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lens diameter is increased to improve resolution, then the resolution is improved, but the device size and complexity increase
Solution Approach 1:
The lens unit is divided into multiple lens groups (first lens group, second lens group, third lens group) with different functions. The first lens group handles oblique illumination, the second handles reflected light collection, and the third handles focus adjustment. This segmentation allows each group to be optimized independently, achieving high resolution without requiring a single large complex lens.
Solution Approach 2:
The patent introduces a beam path that travels through the substrate thickness direction (vertical dimension) rather than only lateral dimensions. The oblique incident light beam passes through the substrate from above, and the reflected light is collected from below, utilizing the third dimension to achieve high resolution imaging without increasing lateral lens diameter.
2Measurement precision
If the focal distance is reduced to improve resolution, then the resolution is improved, but the working space and ease of operation are reduced
Solution Approach 1:
The patent makes the focal distance adjustable by providing a movable lens group (third lens group) that can be shifted along the optical axis. This dynamic adjustment capability allows the system to achieve high resolution at reduced focal distance while maintaining ease of operation through motorized or manual positioning mechanisms.
Solution Approach 2:
The lens unit is segmented into multiple groups with independent movement capabilities. The third lens group can be shifted to adjust focal distance, while the first and second lens groups maintain fixed positions for stable illumination and light collection. This segmentation allows focal distance adjustment without affecting other functional aspects.
3Measurement precision
If oblique illumination is used to detect groove-shaped defects, then the detection capability is improved, but the light path obstruction increases
Solution Approach 1:
The patent utilizes the vertical dimension by passing the oblique incident light beam through the substrate thickness direction. The light enters from above at an oblique angle, reflects off surface defects, and the reflected beam is collected from below. This vertical path arrangement eliminates lateral obstruction issues and enables effective detection of groove-shaped defects.
Solution Approach 2:
The optical path is segmented into separate functional zones: the first lens group for oblique illumination, the substrate region for light interaction, and the second lens group for reflected light collection. This segmentation allows oblique illumination to be implemented without light path obstruction by spatially separating the illumination and collection paths.
4Measurement precision
If multiple beam paths are implemented to improve resolution, then the resolution and detection accuracy are improved, but the device complexity increases
Solution Approach 1:
The lens unit is designed with multi-functionality where the first lens group serves both as an illumination system for oblique incident light and as part of the imaging system. The second lens group simultaneously collects reflected light and focuses it onto the imaging sensor. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall device complexity while maintaining high detection accuracy.
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 allows for improved resolution and precise defect detection by maintaining unobstructed light paths, even with increased lens diameter and reduced focal distance, effectively addressing the limitations of conventional tools and enhancing image clarity for surface defects.
Implementation Method 1
a lens unit (60, 57, 59) and a chuck (53) located below the lens unit
Implementation Method 2
When surface defects SD such as particles or scratches exist on the surface of the substrate 1, the second incident light 9b is irregularly reflected from the defect surfaces to generate scattered light 9s
Data Source
AI summary
An optical inspection tool used to detect surface defects of a substrate include a chuck for holding a substrate and a lens unit disposed over the chuck. The lens unit includes at least a pair of oblique beam paths therein, wherein light penetrating the beam paths travels without angular deflection. The beam paths take the form of spaces formed through the lens unit, or flat portions formed on a lens within the lens unit. A camera is installed on the lens unit, and the camera converts light passing through the lens unit into an image. Methods of detecting surface defects of the substrate using the inspection tool are also provided.