Adaptive EUV Mirror Piezoelectric Layer 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, achieving high surface quality while preventing interference from metallic structures and piezoelectric layers during interferometric measurements is challenging, leading to corrupted measurement results.
Innovation Solution
A multifunctional layer system is introduced, which includes a piezoelectric layer between the mirror substrate and the reflection layer stack, with electrode arrangements that enable a smoothing surface processing and allow for interferometric measurements by minimizing electromagnetic radiation transmission, typically below 10−6, thus preventing interference from metallic structures during the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a piezoelectric layer with electrode arrangements is used for adaptive mirror functionality, then the mirror can compensate for imaging aberrations, but the metallic structures and piezoelectric layer interfere with interferometric measurements during fabrication
Solution Approach 1:
The fabrication process is segmented into distinct phases: first fabricating the mirror structure with piezoelectric layer and electrodes, then removing this structure after it has served its purpose during assembly and alignment. This allows the adaptive functionality to be present during critical phases while eliminating measurement interference later.
Solution Approach 2:
The adaptive mirror structure with piezoelectric layer and electrodes is fabricated and positioned in advance, before interferometric measurements are performed. This preliminary action allows the structure to be in place during assembly and alignment, but removed before measurements to avoid interference.
2Reliability
If the mirror structure is optimized for EUV reflection, then optical performance in the EUV range is improved, but surface quality and interferometric measurability become difficult to achieve simultaneously
Solution Approach 1:
The mirror substrate and reflection layer stack are fabricated with high precision surface quality in advance, before the piezoelectric layer and electrodes are added. This ensures that the critical optical surface is already optimized for EUV reflection, and the adaptive structure is added subsequently without compromising the pre-established surface 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
This solution ensures high surface quality and accurate interferometric measurements by reducing the influence of metallic structures on measurement results, allowing for precise material removals and improved optical performance in the EUV range.
Implementation Method 1
it is also known to configure one or more mirrors in an EUV system as an adaptive mirror with an actuator layer composed of a piezoelectric material, wherein an electric field having a locally varying strength is generated across this piezoelectric layer by an electrical voltage being applied to electrodes arranged on both sides with respect to the piezoelectric layer
Implementation Method 2
a reflection layer stack for reflecting electromagnetic radiation having an operating wavelength that is incident on the optical effective surface
Data Source
AI summary
A mirror having a mirror substrate (12, 32, 52), a reflection layer stack (21, 41, 61) reflecting electromagnetic radiation having an operating wavelength that is incident on the optical effective surface (11, 31, 51), and at least one piezoelectric layer (16, 36, 56), arranged between the substrate and the reflection layer stack and to which an electric field producing a locally variable deformation is applied. A first electrode arrangement (20, 40, 60) situated on the side of the piezoelectric layer faces the reflection layer stack, and a second electrode arrangement (14, 34, 54) is situated on the side of the piezoelectric layer facing the mirror substrate. Optionally, a bracing layer (98) is provided, which limits sinking of the piezoelectric layer (96) into the mirror substrate (92) when an electric field is applied, in comparison with an analogous construction lacking the bracing layer, thereby increasing the piezoelectric layer's effective deflection.