Photomask Inspection Aperture Layout for EUV Defect Detection
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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 symmetrical shape and increased diameter, and the incident radiation tilt angle is tuned to enhance light collection and reduce image distortion, resulting in improved defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing aperture design is used for photomask inspection, then device complexity is maintained at acceptable levels, but image intensity uniformity and quality are insufficient for detecting small defects in advanced semiconductor technologies
Solution Approach 1:
The patent applies asymmetry by transitioning from a symmetrical circular aperture to an asymmetrical rectangular aperture design. This rectangular aperture with specific width and height dimensions enables improved light collection in critical directions while maintaining manufacturing feasibility, thereby enhancing defect detection quality without excessive complexity increase
Solution Approach 2:
The patent implements parameter changes by optimizing the aperture dimensions (width and height), adjusting the tilt angle of the incident radiation beam, and modifying the aperture position relative to the optical axis. These parameter optimizations directly improve image intensity uniformity and defect detection capability while keeping the overall system complexity manageable
2Reliability
If conventional inspection methods are used, then manufacturing processes remain simple, but defect detection effectiveness is insufficient due to image distortion and poor intensity uniformity
Solution Approach 1:
The patent improves reliability by optimizing critical parameters including the rectangular aperture dimensions, the tilt angle of the incident radiation beam relative to the photomask surface, and the aperture position in the projection optics box. These parameter changes enhance image quality and defect detection effectiveness
Solution Approach 2:
The patent replaces conventional mechanical inspection approaches with an optimized optical inspection system that uses precisely controlled radiation beams and aperture geometries. This substitution enables non-contact, high-precision defect detection with improved reliability
3Illumination intensity
If standard aperture design is used, then manufacturing and operation remain straightforward, but light collection efficiency is insufficient leading to poor image quality
Solution Approach 1:
The patent employs asymmetry in the aperture design by using a rectangular shape with specifically optimized width and height ratios. This asymmetric design maximizes light collection efficiency in the directions most critical for defect detection while maintaining straightforward manufacturing and operation procedures
Solution Approach 2:
The patent applies local quality by positioning the rectangular aperture at specific locations in the projection optics box and orienting it at particular angles. This localized optimization of aperture position and orientation enhances light collection efficiency without complicating the overall system operation
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 generates inspection images with greater intensity uniformity and reduced distortion, significantly enhancing the effectiveness of defect detection in EUV photomasks.
Implementation Method 1
receive a second radiation beam reflected from the photomask
Data Source
AI summary
An inspection apparatus includes: an inspection apparatus includes: a stage configured to support 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 has a diameter, a minor axis or a diagonal equal to a distance measured from a center of the aperture stop to a periphery the aperture stop.