Mask Blanks Substrate Flatness Control via Height Map Analysis
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Solution Overview
Problem
Current methods for manufacturing mask blanks substrates for EUV lithography fail to achieve sufficient flatness, especially when the exposure mask is held by adsorption on an exposure machine, leading to deterioration in flatness and reduced product yield due to insufficient control over surface shape and directional differences in chucking positions.
Innovation Solution
A method involving local processing and finish polishing steps to calculate and adjust the surface shape of both main surfaces of the mask blanks substrate, converting them into height maps and reverse height maps to create a calculated height map with a flatness of 100 nm or less, ensuring high flatness and accuracy when held by the exposure machine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If double-sided simultaneous polishing is used to manufacture glass substrates, then manufacturing efficiency is improved, but sufficient flatness for EUVL cannot be obtained
Solution Approach 1:
The patent segments the polishing process into multiple stages: initial double-sided simultaneous polishing for efficiency, followed by separate single-sided polishing operations to achieve the required flatness. This segmentation allows the process to benefit from both high-efficiency bulk material removal and precise final surface control.
Solution Approach 2:
The patent performs preliminary double-sided simultaneous polishing to establish a baseline flatness and remove major surface irregularities before proceeding to more precise single-sided polishing operations. This preliminary action prepares the substrate for subsequent fine-tuning of flatness.
2Manufacturing precision
If local processing techniques are used to correct surface shape, then flatness is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies local processing techniques that selectively remove material from specific regions of the substrate surface. By focusing polishing actions only on areas that require correction rather than treating the entire surface uniformly, the method achieves high flatness while minimizing unnecessary processing complexity.
3Reliability
If the back surface is adsorbed on the mask stage during exposure, then the exposure mask is securely held, but the front surface flatness deteriorates due to deformation
Solution Approach 1:
The patent performs preliminary shaping and flatness correction of both the front and back surfaces during manufacturing, anticipating the deformation that will occur during exposure. By pre-correcting the surface shapes, the substrate maintains the required flatness even after adsorption-induced deformation during the exposure process.
Data Source
AI summary
A mask blanks substrate having a flatness of a calculation surface of 100 nm or less when a calculation region passing through central portions of first and second main surfaces and extending in a horizontal direction is set, a first region surface is cut out, a second region surface is cut out by setting a reference plane and a rotation axis and rotating the substrate by 180°, least square planes are calculated, the first and second region surfaces are converted into height maps to positions on the least square planes, the height map of the to second region surface is set as a reverse height map by symmetrically moving the height map, and a map of a calculated height obtained by adding heights of the height map of the first region surface and the reverse height map of the second region surface is set as the calculation surface.