Flare-Measuring Mask for EUV Projection Optical Systems
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Solution Overview
Problem
Conventional flare-measuring methods for projection optical systems, especially those using extreme ultraviolet light, face challenges in accurately measuring flare information across all directions due to increased area without bar-shaped patterns at farther image plane positions, making it difficult to evaluate flare contribution uniformly.
Innovation Solution
A flare-measuring method and mask pattern using aperture patterns with inclined straight line portions and connecting segments, and sectoral patterns arranged symmetrically around a central block area, allowing for accurate flare measurement by projecting images through the optical system and determining light ratios, enabling correct measurement within a predetermined angle range and easy processing on a polar coordinate system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bar-shaped patterns are arranged in multiple directions to evaluate flare anisotropy, then directional flare comparison is improved, but the area without patterns increases at farther image plane positions, reducing measurement accuracy
Solution Approach 1:
The evaluating pattern is segmented into multiple straight line portions (first, second, third, fourth straight line portions) arranged in different directions, each contributing to flare measurement in specific angular ranges. This segmentation allows comprehensive directional coverage while maintaining pattern density across the entire image plane, eliminating the large gap areas problem of conventional methods.
Solution Approach 2:
The invention transitions from conventional two-dimensional rectangular coordinate system arrangements to a polar coordinate system approach, where patterns are arranged radially from the image center. This dimensional change enables uniform angular distribution of measuring points across the image plane, ensuring that flare can be evaluated in all directions without creating large unused areas at the periphery.
2Device complexity
If conventional evaluating patterns are used, then simple pattern structure is maintained, but flare contribution from all directions cannot be evaluated uniformly
Solution Approach 1:
The evaluating pattern employs asymmetric straight line portions with different orientations (first and second straight line portions in one direction, third and fourth in another direction) to systematically probe flare characteristics across different angular ranges. This asymmetric arrangement within a symmetric radial framework enables comprehensive directional measurement while maintaining overall pattern symmetry for ease of manufacture.
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 allows for precise measurement and correction of flare information across all directions, improving the accuracy of pattern correction and image formation on the wafer, even in high-resolution EUV exposure systems.
Implementation Method 1
irradiating the radiation onto the mask to project an image of the pattern via the optical system
Implementation Method 2
if a scattered light, which is generated due to the surface roughness of an optical member constructing a projection optical system, forms any flare as a blur of an image around the image to be imaged by the genuine light flux
Data Source
AI summary
A method for measuring flare information of a projection optical system includes arranging, on an object plane of the projection optical system, a sectoral pattern surrounded by a first side, a second side which is inclined at a predetermined angle with respect to the first side, and an inner diameter portion and an outer diameter portion which connect both ends of the first side and both ends of the second side; projecting an image of the sectoral pattern via the projection optical system; and determining the flare information based on a light amount of the image of the sectoral pattern and a light amount provided at a position away from the image. With the flare measuring method, it possible to correctly measure the flare information in an arbitrary angle range.