Mirror Assembly Coating for Humidity-Stable Optical Surfaces
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Solution Overview
Problem
The deformation of mirror substrates in optical arrangements due to humidity fluctuations in the surroundings, causing aberrations in beam paths, is not adequately addressed by existing technologies, particularly in vacuum-operated EUV and DUV lithography apparatuses.
Innovation Solution
A water vapor diffusion barrier coating is applied to the surface of water vapor-sorbing materials, such as adhesive layers, to reduce the penetration of water vapor and minimize substrate deformations by decoupling forces from actuators, combined with elastic or flexible materials to manage humidity changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If water vapor-sorbing material (adhesive layer) is used to secure actuators on the rear side of the substrate, then the actuators can be mechanically secured, but humidity-induced expansion of the adhesive layer causes substrate deformations and mirror surface drift
Solution Approach 1:
A water vapor diffusion barrier layer is introduced as an intermediary between the water vapor-sorbing adhesive layer and the substrate. This barrier layer mediates the interaction by allowing mechanical bonding while blocking water vapor penetration, preventing adhesive expansion from causing substrate deformations
Solution Approach 2:
The structure uses a composite material system consisting of multiple layers: a water vapor-sorbing adhesive layer for mechanical securement, a water vapor diffusion barrier layer (e.g., SiO2, Al2O3, Ta2O5) to prevent humidity penetration, and the substrate. This composite structure combines the beneficial properties of each material while mitigating their individual drawbacks
2Reliability
If the optical arrangement is operated under vacuum conditions, then beam quality is maintained, but maintenance and repair require interrupting the vacuum, causing humidity fluctuations that induce substrate deformations
Solution Approach 1:
The water vapor diffusion barrier coating is applied beforehand to the adhesive layer to create a protective shield that cushions against humidity fluctuations during maintenance operations. This pre-established barrier prevents water vapor penetration even when vacuum is interrupted, allowing maintenance activities without compromising mirror surface stability
Solution Approach 2:
The diffusion barrier coating serves as a thin, sacrificial protective layer that can be easily applied and replaced. It provides temporary protection during maintenance operations but does not interfere with the long-term vacuum operation or require complex integration with the vacuum system
3Stability of the object's composition
If a water vapor diffusion barrier coating is applied to the adhesive layer, then substrate deformations are reduced, but the device complexity increases
Solution Approach 1:
The invention changes the parameter of water vapor transmission by applying a diffusion barrier coating with specific material properties (low water vapor transmission rate). This parameter change transforms the adhesive layer from being highly permeable to water vapor into a protected structure that maintains substrate stability while adding minimal structural complexity
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 solution effectively reduces substrate deformations and aberrations by minimizing stress transmission from humidity-induced adhesive expansion, allowing for quicker transitions and reduced downtime in optical apparatuses.
Implementation Method 1
a surface of the water vapor-sorbing material, in particular a surface of the adhesive layer, is covered at least partly, in particular completely, by a coating which forms a water vapor diffusion barrier
Implementation Method 2
If the adhesive layer or another water vapor-sorbing material, organic material for example, connected mechanically directly or indirectly to the substrate takes up moisture from the surroundings, this layer or this material expands
Data Source
AI summary
A mirror arrangement (30) includes: a substrate (31) with a front side (31a) having a mirror face (32a) reflecting radiation (5), and a rear side (31b) facing away from the front side and on which at least one actuator (27) generating deformations of the mirror face is arranged. A water vapor (36)-sorbing material (33, 42) is formed on the rear side (31b) and forms an adhesive layer (33) for securing the actuator. The layer extends into interspaces (35) between the actuators (27). A surface (33a, 42a) of the water vapor-sorbing material is covered at least partly by a coating (37) which forms a water vapor diffusion barrier.