Photomask Inspection Aperture for Uniform, Low-Distortion EUV Images
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Solution Overview
Problem
Existing lithography techniques fail to meet the requirements for high-quality photomask image inspection, particularly in advanced semiconductor technologies where defects in EUV photomasks are difficult to identify due to small size and complexity.
Innovation Solution
The inspection apparatus is modified with a redesigned aperture for the inspection radiation beam, featuring a greater diameter and symmetrical shape to increase radiation intensity and reduce image distortion, combined with a tuned tilt angle for improved light collection performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional aperture design is used for inspection radiation beam, then the inspection operation can be performed, but the image intensity uniformity is poor and distortion is high
Solution Approach 1:
The patent applies asymmetry principle by positioning the aperture off-center relative to the optical axis. The aperture is located at a distance of 0.5-2 times the radius of the projection optics box from the optical axis, creating an asymmetric configuration that optimizes light collection from the tilted photomask surface while maintaining acceptable image quality
Solution Approach 2:
The patent applies local quality principle by optimizing the aperture's position and size specifically for the inspection function. The aperture dimensions and location are tailored to match the numerical aperture requirements of the projection optics box, creating locally optimized light collection that improves defect detection in specific regions of the photomask
2Use of energy by moving object
If the aperture diameter is increased to collect more light, then light collection performance improves, but image distortion increases
Solution Approach 1:
The patent applies parameter changes principle by systematically varying the aperture's position parameter (distance from optical axis) and size parameter (diameter) to find the optimal balance. The aperture is positioned at 0.5-2 times the radius of the projection optics box, and its diameter is optimized to collect sufficient light while maintaining image quality within acceptable distortion limits
3Ease of manufacture
If a symmetrical aperture is used, then the design is simple, but it cannot accommodate the tilted illumination required for EUV photomask inspection
Solution Approach 1:
The patent deliberately introduces asymmetry to accommodate the tilted illumination requirement. The aperture is positioned off-center at a distance of 0.5-2 times the projection optics box radius, allowing it to receive radiation from the tilted photomask surface. This asymmetric positioning enables the system to handle the specific geometric requirements of EUV photomask inspection while maintaining a relatively simple single-aperture design
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
The proposed scheme enhances defect detection effectiveness by generating inspection images with greater intensity uniformity and reduced distortion, improving the ability to identify defects in EUV photomasks.
Implementation Method 1
an aperture stop configured to receive a second radiation beam reflected from the photomask through an aperture of the aperture stop
Data Source
AI summary
An inspection apparatus includes: an inspection apparatus includes: a stage configured to receive a photomask; a radiation source configured to emit a first radiation beam for inspecting the photomask; and an aperture stop configured to receive a second radiation beam reflected from the photomask through an aperture of the aperture stop, wherein the aperture is tangent at a center of the aperture stop.