EUV Mirror Layer Stack for Interferometric Measurement
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Solution Overview
Problem
In the production of adaptive mirrors for microlithographic projection exposure apparatuses, especially in the EUV range, interferometric measurements are challenged by the metallic structures and piezoelectric layers, leading to distorted measurement results and inadequate surface processing.
Innovation Solution
A layer stack comprising an absorber layer, an antireflection (AR) layer, and a smoothing layer is introduced between the mirror substrate and the reflection layer system. This configuration absorbs measurement radiation, suppresses reflections, and optimizes the smoothing process, ensuring accurate interferometric measurements and improved surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mediator layer with low electrical conductivity is used between electrodes in the piezoelectric layer, then the potential difference is dropped across the mediator layer enabling piezoelectric actuation, but the metallic structures and piezoelectric layer cause interference in interferometric measurements
Solution Approach 1:
The patent introduces an absorber layer as an intermediary between the mirror substrate (containing metallic electrode structures) and the measurement environment. This absorber layer specifically absorbs the electromagnetic radiation that would otherwise be scattered by the metallic structures, thereby eliminating measurement interference while preserving the piezoelectric actuation function below
Solution Approach 2:
The patent extracts the harmful scattering function from the metallic electrode structures by placing an absorber layer over them. This layer selectively removes (absorbs) the problematic electromagnetic radiation interactions, allowing the underlying piezoelectric structures to maintain their actuation function without causing measurement interference
2Adaptability or versatility
If the mirror substrate contains metallic electrode structures and piezoelectric layers for adaptive control, then the mirror can compensate for optical aberrations, but the surface quality and optical processibility are compromised due to interference from hidden structures
Solution Approach 1:
The absorber layer serves as a mediator that decouples the adaptive control function from the optical measurement process. It allows the metallic electrode structures to remain functional for aberration compensation while preventing them from interfering with surface quality measurements and optical processing
Solution Approach 2:
The patent converts the harmful effect of metallic structures (which scatter measurement radiation and degrade surface quality measurements) into a beneficial configuration by placing an absorber layer above them. This layer specifically targets and absorbs the interfering radiation, allowing the adaptive mirror structures to function without compromising manufacturing precision
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 proposed layer stack effectively prevents interference from hidden structures in the mirror substrate, allowing for precise interferometric measurements and enhanced optical processibility, thereby achieving higher surface quality and compliance with EUV specifications.
Implementation Method 1
an absorber layer, an antireflection (AR) layer and a smoothing layer
Implementation Method 2
an absorber layer, an antireflection (AR) layer and a smoothing layer
Data Source
AI summary
A mirror, in particular for a microlithographic projection exposure system, having an active optical surface, a reflective layer system for reflecting electromagnetic radiation of a working wavelength which is incident on the active optical surface, a mirror substrate (105, 205, 305) which is made of a mirror substrate material and in which structures (106, 206, 306) are arranged that differ from the surrounding mirror substrate material in terms of the refractive index, and a layer stack which is located between the mirror substrate (105, 205, 305) and the reflective layer system. The layer stack has an absorber layer (110, 210, 310) an AR layer (120, 220, 320) and a smoothing layer (130, 230, 330) one after the other in a stacking direction running from the mirror substrate (105, 205, 305) to the reflective layer system.