EUV Mask Protection Layer for LTEM Substrate Particle Control
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Solution Overview
Problem
EUV photomasks face issues with image accuracy due to out-of-band light and particle contamination during the EUV wafer printing process, which can cause pattern errors and damage to the low thermal expansion material (LTEM) substrate.
Innovation Solution
A protection layer is deposited on the LTEM substrate, functioning as an etch stop and reducing particle generation during EUV irradiation, while retaining some reflective multilayers to maintain high reflectivity and control critical dimension errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the LTEM substrate is exposed during EUV wafer printing, then the substrate can be directly irradiated, but particles may be introduced and migrate to pattern regions causing image errors
Solution Approach 1:
A protection layer is introduced as an intermediary between the LTEM substrate and the EUV environment. This protection layer serves as a barrier that prevents particle migration from the substrate to the pattern regions while allowing the substrate to remain exposed for efficient EUV wafer printing. The protection layer thus mediates between the conflicting requirements of productivity and manufacturing precision.
2Reliability
If a protection layer is deposited on the LTEM substrate, then particle migration is limited and substrate damage is reduced, but the structure complexity increases
Solution Approach 1:
Instead of adding complex structural elements, a thin film protection layer is deposited on the LTEM substrate. This thin film approach provides effective particle barrier protection while minimizing the increase in structural complexity. The protection layer is a simple, uniform coating that maintains the overall simplicity of the mask structure.
3Object-affected harmful factors
If all reflective multilayers are removed in the black border region, then neighbor-die issues are limited, but reflectivity in image fields may be affected
Solution Approach 1:
The protection layer is applied selectively to different regions of the substrate with different functions. In the black border region, the protection layer works alongside partial multilayer removal to limit neighbor-die issues. In the image fields, the protection layer preserves reflectivity by preventing particle contamination. This local differentiation of protection strategies resolves the contradiction between reducing harmful effects and maintaining illumination quality.
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
The protection layer minimizes EUV light reflection from the image border, reduces substrate damage, and limits particle migration, thereby enhancing pattern accuracy and preventing image errors.
Implementation Method 1
the protection layer protects the substrate against an extreme ultraviolet (EUV) irradiation
Implementation Method 2
The protection layer minimizes EUV light reflection from the image border, reduces substrate damage, and limits particle migration
Data Source
AI summary
Fabricating a photomask includes forming a protection layer over a substrate. A plurality of multilayers of reflecting films are formed over the protection layer. A capping layer is formed over the plurality of multilayers. An absorption layer is formed over capping layer. A first photoresist layer is formed over portions of absorption layer. Portions of the first photoresist layer and absorption layer are patterned, forming first openings in absorption layer. The first openings expose portions of the capping layer. Remaining portions of first photoresist layer are removed and a second photoresist layer is formed over portions of absorption layer. The second photoresist layer covers at least the first openings. Portions of the absorption layer and capping layer and plurality of multilayer of reflecting films not covered by the second photoresist layer are patterned, forming second openings. The second openings expose portions of protection layer and second photoresist layer is removed.