Defect Inspection Illumination System for Narrow Wafer Scanning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional defect inspection methods for semiconductor wafers face challenges in efficiently changing the incidence angle of illumination light with a narrow illumination width, leading to reduced inspection speed and increased costs due to the need for expensive high-output lasers and complex lens or mirror replacements.
Innovation Solution
A defect inspection device with an illumination optical system that includes a laser light source, beam expander, anamorphic optical unit, cylindrical optical unit, and relay lens, allowing for precise control of illumination angle, direction, and polarization, along with optical coatings to reduce power loss, enabling efficient illumination of a narrow region on the wafer without the need for expensive mirror or lens changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a cylindrical lens or mirror is used to condense light to a narrow width (1-2 μm or smaller), then the illumination width is reduced, but the wavefront aberration increases and requires precise curvature or thickness control
Solution Approach 1:
The illumination optical system is divided into multiple functional components: a cylindrical lens for initial light condensation, a movable stage for position adjustment, and a relay lens for final image formation. This segmentation allows each component to be optimized independently, with the cylindrical lens handling the narrow width requirement and the relay lens correcting any aberrations and positioning the final image accurately.
Solution Approach 2:
A relay lens is introduced as an intermediary between the cylindrical lens and the wafer. The relay lens serves as a mediator that takes the light from the cylindrical lens, corrects wavefront aberrations, and forms the final narrow illumination image on the wafer surface. This intermediary component enables the system to achieve narrow illumination width while maintaining acceptable wavefront quality.
2Measurement precision
If the incidence angle is changed to 60 or 70 degrees to match target defects, then defect detection capability is improved, but the illumination intensity decreases due to light spread
Solution Approach 1:
The system employs a movable stage that can dynamically adjust the position of the cylindrical lens and relay lens assembly. This dynamic positioning capability allows the system to optimize the illumination geometry for different defect types and incidence angles without changing the optical components themselves, thereby maintaining high illumination intensity across various inspection configurations.
Solution Approach 2:
The system changes operational parameters (positioning coordinates of the movable stage, focal length of relay lens) rather than changing the physical optical components to achieve different incidence angles. This parameter-based adjustment maintains the narrow illumination width and high intensity while adapting to different defect detection requirements.
3Adaptability or versatility
If replaceable cylindrical lenses or mirrors are used to change incidence angle, then adaptability to different defect types is improved, but the time to replace components increases
Solution Approach 1:
Instead of using replaceable optical components, the system employs a dynamic movable stage that can be positioned at different coordinates to achieve various incidence angles. This dynamic positioning system eliminates the need for physical component replacement, allowing rapid adjustment between different inspection configurations without stopping or manual intervention.
Solution Approach 2:
The movable stage serves multiple functions: it positions the cylindrical lens, adjusts the incidence angle, and optimizes the illumination geometry for different defect types. This single multi-functional component replaces what would otherwise require multiple specialized optical elements, reducing complexity and adjustment time.
4Illumination intensity
If a high output laser is used to maintain illumination intensity with narrow width, then illumination intensity is maintained, but the cost increases
Solution Approach 1:
The illumination system segments the light path into distinct functional stages: a cylindrical lens for initial condensation, a movable stage for positioning, and a relay lens for final image formation. This segmentation allows the use of a standard laser source combined with optimized optical components rather than requiring a high-output laser, reducing overall system cost while maintaining illumination intensity.
Solution Approach 2:
The relay lens creates an optical copy or image of the light from the cylindrical lens, concentrating it into the final narrow illumination pattern on the wafer. This optical copying process efficiently delivers high intensity to the target area without requiring the laser source itself to be high-power, as the relay lens concentrates the available light energy.
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 solution allows for improved inspection sensitivity with a narrow illumination width, reduced costs by using lower output lasers, and enhanced illumination efficiency, while maintaining high inspection speed and accuracy.
Implementation Method 1
a cylindrical optical unit which condenses the laser beam passed through the anamorphic optical unit in one direction and forms a linearly condensed light image as an intermediate image
Implementation Method 2
a relay lens unit which forms the linearly condensed light image on a surface of the specimen mounted on the table unit to illuminate a linear region on the specimen
Implementation Method 3
a polarization condition of the laser beam passing through the anamorphic optical unit and the cylindrical optical unit is a specific linearly polarized condition, wherein optical coatings are applied to surfaces of a cylindrical lens of the cylindrical optical unit, said optical coating corresponding to the polarization state of the laser beam to reduce power loss of the laser beam
Data Source
AI summary
To increase the illumination efficiency by facilitating the change of the incident angle of illumination light with a narrow illumination width according to an inspection object and enabling an illumination region to be effectively irradiated with light, provided is a defect inspection method for obliquely irradiating a sample mounted on a table that is moving continuously in one direction with illumination light, collecting scattered light from the sample obliquely irradiated with the illumination light, detecting an image of the surface of the sample formed by the scattered light, processing a signal obtained by detecting the image formed by the scattered light, and extracting a defect candidate, wherein the oblique irradiation of the light is implemented by linearly collecting light emitted from a light source, and obliquely projecting the collected light onto the surface of the sample, thereby illuminating a linear region on the surface of the sample.