Stress Relief Heating for EUV Mirror Capping Layers
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Solution Overview
Problem
Current capping layers for EUVL mirrors are inadequate in preventing oxidation, leading to reduced reflectivity and shorter lifetimes, as they fail to maintain integrity over the required 30,000 hours due to internal stress relaxation in multi-layer mirror elements.
Innovation Solution
The method involves heating the multi-layer material stacks to reduce internal stress before forming capping layers, ensuring a stress-free surface and preventing oxidation, thereby extending the EUV optics lifetime and maintaining reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capping layers are deposited on multi-layer mirror element surfaces without stress relief, then the capping layers develop cracks due to internal stress relaxation, but if the system is heated to relieve stress, then the multi-layer mirror element structure is damaged due to intermixing
Solution Approach 1:
The patent applies preliminary stress relief treatment to the multi-layer mirror element before depositing the capping layer. By performing the stress relief operation beforehand, the internal stress is reduced prior to capping layer formation, preventing subsequent crack development in the capping layer while avoiding damage to the multi-layer structure that would occur with post-deposition heating.
2Object-affected harmful factors
If the vacuum system is baked at high temperature to reduce water vapor, then the vacuum quality improves, but the EUV optics alignment and multi-layer mirror element quality are damaged
Solution Approach 1:
The patent performs stress relief treatment on the multi-layer mirror element before capping layer deposition, which addresses the internal stress issue without requiring high-temperature baking of the entire vacuum system. This preliminary action reduces the need for aggressive vacuum baking, thereby preserving EUV optics alignment while still achieving adequate vacuum quality.
3Ease of manufacture
If capping layers are formed without prior stress relief, then the deposition process is simpler, but the capping layers crack and fail to prevent oxidation over time
Solution Approach 1:
The patent incorporates a stress relief step before capping layer deposition to ensure long-term oxidation prevention. By performing this preliminary stress relief treatment, the capping layer is deposited on a stress-reduced substrate, preventing future crack formation and maintaining oxidation protection for the required 30,000 hours, thus balancing manufacturing simplicity with long-term durability.
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 results in a more stable and reliable capping layer, increasing the EUV optics lifetime, preventing oxidation, and maintaining reflectivity, thus enabling high-volume production viability for EUV lithography systems.
Implementation Method 1
heating the reflective material reduces the internal stress of at least the top portion of the reflective material
Implementation Method 2
heating the reflective material reduces the internal stress of at least the top portion of the reflective material
Data Source
AI summary
A reflective material is heated to reduce internal stress, and then a capping layer is formed over the reflective material. Heating the reflective material reduces the internal stress of the reflective material. Because the reflective material has reduced internal stress, a more continuous, stable and reliable capping layer is formed that is not subject to stress induced degradation over time due to the relaxing internal stress of the underlying reflective material. Thus, the capping layer remains intact and protects the reflective material residing beneath the capping layer from exposure to contaminants.