Anamorphic EUV Mask Measurement System for High NA Lithography
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Solution Overview
Problem
High NA EUV lithography processes face challenges in efficiently measuring and correcting mask patterns due to the asymmetry in reduction ratios, leading to low productivity and increased costs in defect inspection and correction processes, especially when using anamorphic optical systems.
Innovation Solution
A high-performance anamorphic aerial image measuring system utilizing a coherent EUV light source, an x-ray toroidal mirror, an x-ray beam splitter, an anamorphic zone-plate lens, and an anamorphic photo sensor to focus and measure EUV light with different numerical apertures in horizontal and vertical directions, allowing for noise removal and high-resolution pattern analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high NA EUV scanner with anamorphic optical system is used to achieve NA value of 0.55 or larger, then the resolution and pattern formation capability are improved, but the device complexity and manufacturing difficulty increase due to asymmetric reduction ratios in different directions
Solution Approach 1:
The patent applies asymmetry principle by designing an anamorphic optical system with different reduction ratios in orthogonal directions (1:8 in scanning direction, 1:4 in perpendicular direction). This asymmetric configuration enables achieving high NA value of 0.55 or larger while maintaining the required resolution for scaled-down semiconductor devices with half pitch of 16 nm or less
Solution Approach 2:
The optical system is segmented into distinct functional components with specific reduction ratios: a first optical system providing 1:8 reduction in the scanning direction and a second optical system providing 1:4 reduction in the perpendicular direction. This segmentation allows independent optimization of each direction's optical path to achieve the desired high NA while managing system complexity
2Manufacturing precision
If the reduction ratio is decreased from 1:4 to 1:8 to achieve higher NA value, then the numerical aperture is improved, but the productivity of pattern exposing process deteriorates
Solution Approach 1:
The patent resolves this contradiction by applying asymmetric reduction ratios in different directions rather than uniformly decreasing the reduction ratio. The 1:8 reduction is applied only in the scanning direction to achieve NA 0.55, while the 1:4 reduction is maintained in the perpendicular direction to preserve productivity. This directional asymmetry allows selective optimization of resolution without sacrificing overall exposing efficiency
3Manufacturing precision
If mask patterns are manufactured with asymmetry in pattern size to suit anamorphic optical system, then the pattern accuracy on wafer is improved, but the mask manufacturing complexity and inspection difficulty increase
Solution Approach 1:
The patent addresses mask manufacturing complexity by systematically applying asymmetry principle. Mask patterns are designed with predetermined asymmetric dimensions that correspond to the anamorphic optical system's reduction ratios. By pre-calculating and pre-configuring the asymmetric pattern sizes, the patent simplifies the manufacturing process compared to attempting to correct asymmetric distortions after pattern formation
Solution Approach 2:
The patent applies preliminary action by pre-designing and pre-configuring asymmetric mask patterns before the exposing process. The mask patterns are manufactured with predetermined asymmetric dimensions that anticipate the anamorphic reduction, eliminating the need for complex post-exposure corrections and simplifying both manufacturing and inspection processes
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
Enables accurate and efficient measurement of EUV mask patterns with improved resolution and productivity, reducing wafer-level defects and increasing yield by effectively addressing the asymmetry in anamorphic optical systems.
Implementation Method 1
an x-ray toroidal mirror focusing the generated EUV light on an incidence surface to have different focal lengths in horizontal and vertical directions of the incidence surface
Implementation Method 2
an anamorphic zone-plate lens focusing the transmitted portion of the beam emitted from the x-ray beam splitter on the mask, the anamorphic zone-plate lens having the same focal length and different numerical apertures (NA) in a vertical direction of an incidence surface
Implementation Method 3
an anamorphic photo sensor, which is configured to measure an energy of the reflected portion of the coherent EUV light when the coherent EUV light is reflected by the EUV mask
Data Source
AI summary
A system of measuring an image of a pattern in a high NA scanning-type extreme ultra-violet (EUV) mask is disclosed. The system may include a light source generating an EUV light; an toroidal mirror; an flat mirror allowing light, which is reflected by the toroidal mirror, to be incident into the mask; an beam splitter; a light detection part; an anamorphic zone-plate lens focusing a transmitted portion of a light emitted from the beam splitter on the mask; a stage; and an anamorphic photo sensor, which is configured to measure an energy of a reflected portion of the coherent EUV light, is composed of a detector array, and has different sizes from each other in horizontal and vertical directions of an incidence surface of the detector array.