EUV Mirror Coating Layer Thickness Deviation Compensation
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Solution Overview
Problem
In microlithographic projection exposure systems, particularly in EUV mirrors, layer thickness errors and drifting during the coating process lead to significant impairments in the optical system's performance due to the propagation of small deviations in individual layers within periodically constructed multi-layer systems.
Innovation Solution
A method involving the virtual subdivision of the mirror's layer structure into two or more layer systems with individually specified target layer thickness profiles, where these profiles are selected to compensate for deviations from the overall target layer thickness profile, reducing the maximum deviation by at least 50% over the optical effective area and minimizing the impact on reflectivity profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single target layer thickness profile is specified for the entire layer structure, then the manufacturing process is simple, but layer thickness errors and drifting propagate systematically leading to significant wavefront errors
Solution Approach 1:
The patent divides the layer structure into multiple layer systems (e.g., first layer system with layers 1-10, second layer system with layers 11-20) and assigns different target layer thickness profiles to each system. This segmentation allows independent optimization of each subsystem's thickness profile to compensate for coating errors, resolving the contradiction between manufacturing simplicity and precision by distributing the precision requirement across multiple manageable segments rather than demanding perfect uniformity across the entire structure.
Solution Approach 2:
The patent applies different target layer thickness profiles to different layer systems based on their specific positions and functions within the mirror. Each layer system receives a customized thickness profile tailored to its local requirements, allowing systematic compensation for coating errors in specific regions while maintaining overall mirror performance. This local quality approach enables precise control where needed without unnecessarily complicating the entire manufacturing process.
2Manufacturing precision
If individual target layer thickness profiles are specified for multiple layer systems, then manufacturing precision and wavefront error are reduced, but the complexity of the coating process increases
Solution Approach 1:
By segmenting the layer structure into distinct layer systems with individually optimized target profiles, the patent manages complexity through structured division rather than uncontrolled detail. Each segment's complexity is bounded and manageable, and the systematic approach to defining profiles for each segment prevents exponential growth in overall process complexity while maintaining high precision.
Solution Approach 2:
The patent modifies the target layer thickness profile parameter differently for each layer system rather than using a single uniform profile. This parameter change strategy allows precise control over the coating process for each subsystem, enabling compensation for systematic errors without requiring complete redesign of the entire coating process, thus limiting the increase in complexity to manageable parameter adjustments.
3Ease of manufacture
If uniform target layer thickness is applied across all layers, then the coating process is straightforward, but small deviations lead to significant impairments in optical system performance
Solution Approach 1:
The patent recognizes that different layer systems have different sensitivities to thickness variations and assigns locally optimized target profiles to each. This local quality approach ensures that each layer system's thickness profile is tailored to its specific optical function and error susceptibility, thereby improving overall optical system reliability without requiring uniformly ultra-precise control across all layers, which would be unnecessarily complex.
Solution Approach 2:
The patent changes the target layer thickness parameter systematically across different layer systems rather than maintaining a uniform value. This parameter variation strategy allows the coating process to proactively compensate for expected deviations in different regions, improving optical system reliability by addressing error sources locally rather than relying on uniform precision that is difficult to achieve in practice.
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 effectively reduces the overall deviation from the desired layer thickness profile and wavefront error, enhancing the optical system's performance by compensating for unavoidable errors in the coating process, particularly in EUV mirrors with periodic multi-layer systems.
Implementation Method 1
magnetron coating systems are used to produce mirrors
Implementation Method 2
the respective deviations of the individual target layer thickness profiles from the specified target layer thickness profile compensate at least partially in their contribution to the wavefront effect of the mirror
Data Source
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AI summary
The invention relates to a method for producing a mirror and to a mirror, in particular for a microlithographic projection exposure apparatus. In a method according to the invention, a mirror substrate is coated in a coating apparatus by applying a predefined layer structure for achieving a predefined target layer thickness profile of the mirror, wherein the method comprises the following steps: visually subdividing the predefined layer structure into at least two layer systems (610, 710, 620, 720, 730), and coating the mirror substrate (605, 705) by applying the at least two layer systems with different individual target layer thickness profiles being provided for said layer systems, wherein said individual target layer thickness profiles are chosen such that each of the deviations of the individual target layer thickness profiles from the predefined target layer thickness profile at least partially compensates in the contribution thereof to the wavefront effect of the mirror.