EUV Mask Blank Substrate Flatness Control
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Solution Overview
Problem
Current methods for manufacturing substrates for EUV lithography mask blanks fail to achieve sufficient flatness, particularly in reducing the short-wavelength component of surface shapes, which limits the effectiveness of wavefront correction and affects exposure accuracy.
Innovation Solution
A method involving local processing and finish polishing steps to set a predetermined calculation region on the substrate surfaces, where the shape is evaluated and smoothed using a Gaussian filter to achieve flatness of 100 nm or less, with a difference of 20 nm or less between the highest and lowest values, and further refined to reduce short-wavelength components using a hard polishing cloth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If double-sided simultaneous polishing is used for manufacturing glass substrates, then manufacturing efficiency is improved, but sufficient flatness for EUVL cannot be obtained
Solution Approach 1:
The patent divides the polishing process into two distinct stages: double-sided simultaneous polishing for initial flatness and local processing for final precision. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between efficiency and precision.
Solution Approach 2:
The double-sided simultaneous polishing is performed as a preliminary action to achieve baseline flatness before the local processing step. This preliminary action removes large-scale irregularities efficiently, setting the stage for the subsequent precision work.
2Manufacturing precision
If local processing technique is used to correct flatness by removing convex regions, then flatness is improved, but short-wavelength surface components remain that limit wavefront correction effectiveness
Solution Approach 1:
The patent replaces traditional mechanical local processing with a new approach that includes finish polishing with specific polishing cloths. This substitution reduces short-wavelength surface components that mechanical processing cannot eliminate, thereby improving wavefront correction effectiveness.
Solution Approach 2:
The patent changes the polishing parameters by using specific polishing cloth types and adjusting polishing conditions to target and reduce short-wavelength surface components. This parameter change allows the process to achieve both flatness and surface smoothness required for effective wavefront correction.
3Ease of manufacture
If conventional polishing methods are used, then manufacturing process is simple, but flatness reaches a plateau and cannot be further improved
Solution Approach 1:
The patent implements a continuous multi-stage polishing process where each stage builds upon the previous one. The process continues through double-sided polishing, local processing, and finish polishing with hard and soft cloths, ensuring continuous improvement of flatness without reaching a plateau.
4Ease of manufacture
If short-wavelength surface components are not reduced, then manufacturing process remains simple, but wavefront correction function becomes less effective for future miniaturization
Solution Approach 1:
The patent performs finish polishing with hard and soft polishing cloths as a preliminary action to reduce short-wavelength surface components before the substrate is used for EUVL applications. This preliminary action ensures the substrate is pre-optimized for future wavefront correction requirements and miniaturization needs.
Solution Approach 2:
The patent applies multiple polishing steps with different cloth types to cushion against future performance limitations. By reducing short-wavelength components in advance, the substrate is prepared to withstand the demands of future EUVL miniaturization and wavefront correction technologies.
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 enables the production of substrates with highly flat surfaces that can be accurately wavefront-corrected, enhancing exposure mask performance and achieving better transfer accuracy in EUV lithography.
Implementation Method 1
a local processing step and a finish polishing step subsequent to the local processing step
Data Source
AI summary
A substrate for mask blanks having first and second main surfaces of 152 mm×152 mm square and a thickness of 6.35 mm, wherein: when a range of 132 mm×132 mm square centered on an intersection of diagonal lines is defined as a calculation region in each of the first and second main surfaces, on a substrate surface of the calculation region of at least one of the first and second main surfaces, flatness of the substrate surface of the calculation region based on a least square plane is 100 nm or less, and a difference (PV) between a highest value and a lowest value of a height of a calculation surface represented by a difference between shapes of the substrate surfaces before and after smoothing processing with a Gaussian filter (10 mm×10 mm) based on the least square plane is 20 nm or less.