Light Shaping Diffusers for Semiconductor Inspection Illumination
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Solution Overview
Problem
Optical inspection systems for semiconductor objects face issues with illumination loss and non-uniform illumination due to oblique Kohler illumination, resulting in degraded images and inefficiencies in defect identification.
Innovation Solution
The integration of light shaping diffusers in the optical path to adjust the angular distribution and shape of illuminating light, matching the illuminated area to the imaged area and minimizing intensity outside the imaged region, thereby achieving more uniform and efficient illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If oblique Kohler illumination is used to illuminate the semiconductor object, then the illumination area can be adjusted, but the illuminated area becomes elliptical with high aspect ratio causing illumination loss
Solution Approach 1:
The patent introduces a light shaping diffuser that transforms the circular angular distribution of light from the source into an elliptical angular distribution. This asymmetric transformation matches the elliptical illuminated area shape on the semiconductor object, ensuring that light is concentrated within the imaged area boundaries rather than spilling outside, thereby reducing illumination loss while maintaining adequate illumination area.
2Illumination intensity
If oblique illumination is used to illuminate the object, then illumination area can be controlled, but non-uniform illumination intensity occurs across the illuminated area
Solution Approach 1:
The light shaping diffuser creates different local illumination characteristics across the illuminated area. By engineering the diffuser with varying optical properties at different locations, it compensates for the non-uniform intensity distribution caused by oblique illumination, ensuring more uniform illumination across the entire illuminated area including regions at different distances from the light source.
3Area of stationary object
If the illuminated area is set larger to cover the imaged area, then complete coverage is achieved, but illumination loss increases due to light outside the imaged area
Solution Approach 1:
The patent addresses the area coverage problem by transforming the angular distribution of light in angular space rather than directly in object space. The light shaping diffuser modifies the angular characteristics of light rays, which then naturally converge to illuminate the precise area needed on the semiconductor object, achieving complete coverage of the imaged area without excessive spill-out and illumination loss.
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 approach reduces illumination loss and non-uniformities, leading to improved image quality and more effective defect identification in semiconductor inspection systems.
Implementation Method 1
an optical inspection tool can include a light source and/or other components configured to direct light to an object under inspection... one or more light shaping diffusers in an optical path between the light source and the object under inspection
Data Source
AI summary
An optical inspection system or tool can be configured to adjust the distribution of light by using one or more diffusers. The diffusers can be variable in some embodiments. For example, the angular or spatial distribution of the illumination can be adjusted to minimize intensity of illumination outside of an imaged area to thereby reduce illumination loss. The angular or spatial distribution may additionally or alternatively be adjusted so that the illumination across an illuminated area is substantially uniform. The use of one or more diffusers may aid in the inspection of semiconductor objects including, but not limited to, semiconductor wafers and the like.