EUV Mask Absorber Embedded in Multilayer Stack
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Solution Overview
Problem
Current EUV mask blanks with thick absorber layers on top of the multilayer stack face challenges in achieving precise flatness and are not suitable for next-generation high numerical aperture EUV scanners due to the mask 3D effect, which deteriorates the resolution of extreme ultraviolet lithography.
Innovation Solution
The absorber layer is embedded within the capping layer and the multilayer stack, with the absorber layer top surface flush with the capping layer top surface, minimizing the mask 3D effect and improving the structural design of EUV mask blanks to enhance reflectivity and reduce defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick absorber layer is placed on top of the multilayer stack, then the absorber layer provides sufficient absorption, but the mask 3D effect deteriorates and flatness precision is compromised
Solution Approach 1:
The absorber layer is nested within the multilayer stack structure, specifically embedded in the third reflective layer pair from the substrate side. This nesting approach allows the absorber to be integrated into the existing structural framework rather than added as a separate external layer, thereby maintaining the overall flatness and precision of the mask blank surface while still providing the necessary absorption functionality.
Solution Approach 2:
Instead of placing the absorber layer in the traditional external position (adding thickness in the vertical dimension), the absorber is positioned within the layered structure at a specific depth. This dimensional repositioning allows the absorber to be embedded without increasing the external profile height, thus avoiding the mask 3D effect while maintaining absorption effectiveness.
2Reliability
If a thick absorber layer is placed on top of the multilayer stack, then the absorber layer provides sufficient absorption, but the resolution of EUV lithography deteriorates
Solution Approach 1:
The absorber layer is nested within the multilayer stack structure, specifically embedded in the third reflective layer pair from the substrate side. This nesting approach allows the absorber to be integrated into the existing structural framework rather than added as a separate external layer, thereby maintaining the overall flatness and precision of the mask blank surface while still providing the necessary absorption functionality.
Solution Approach 2:
Instead of placing the absorber layer in the traditional external position (adding thickness in the vertical dimension), the absorber is positioned within the layered structure at a specific depth. This dimensional repositioning allows the absorber to be embedded without increasing the external profile height, thus avoiding the mask 3D effect while maintaining absorption effectiveness.
3Manufacturing precision
If the absorber layer is embedded in the capping layer and multilayer stack, then the mask 3D effect is minimized, but the manufacturing process becomes more complex
Solution Approach 1:
The multilayer stack is segmented into multiple reflective layer pairs, with the absorber layer specifically embedded in the third pair from the substrate side. This segmentation allows for targeted placement of the absorber within a specific section of the stack, simplifying the manufacturing process by focusing the embedding operation on a defined region rather than requiring complex integration throughout the entire structure.
Solution Approach 2:
The absorber layer is deposited onto the third reflective layer pair before the capping layer is formed. This preliminary action ensures that the absorber is properly positioned and secured within the multilayer stack structure prior to final assembly, simplifying subsequent manufacturing steps and ensuring precise alignment without requiring complex post-processing operations.
4Manufacturing precision
If the absorber layer top surface is flush with the capping layer top surface, then the mask 3D effect is minimized, but the etching process becomes more difficult
Solution Approach 1:
The capping layer serves as an intermediary protective layer that is deposited over the multilayer stack and absorber layer. This intermediary layer provides a uniform, protective surface that facilitates the etching process by allowing precise control of the etch depth and pattern transfer, while the absorber layer remains embedded beneath at a controlled depth, maintaining flush alignment with the capping layer top surface.
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 design mitigates the mask 3D effect, allowing for improved image placement and overlay accuracy, enabling the use of EUV mask blanks in next-generation high numerical aperture EUV scanners with enhanced reflectivity and reduced defects.
Implementation Method 1
a reflective multilayer stack 12 on a substrate 14, which reflects EUV radiation at unmasked portions by Bragg interference
Data Source
AI summary
Extreme ultraviolet (EUV) mask blanks, methods for their manufacture and production systems therefor are disclosed. The EUV mask blanks comprise a substrate; a multilayer stack of reflective layers on the substrate; a capping layer on the multilayer stack of reflecting layers; and an absorber layer embedded in the multilayer stack of reflective layers.