EUV Mirror Shielding Layer for Piezoelectric Deformation Control
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Solution Overview
Problem
In microlithographic projection exposure systems, EUV mirrors experience heating-induced thermal expansion and deformation, leading to imaging errors, and the electric field from electrode supply lines causes uncontrollable mirror deformation due to different thermal expansion coefficients of materials, resulting in aberrations and undesirable mirror deformation.
Innovation Solution
A mirror design with a shielding layer made of electrically conductive material is implemented to shield the electric field from electrode leads, and a mediator layer with low conductivity is used to mediate potential between electrodes, while a piezoelectric layer enables locally variable deformation for aberration correction, with the shielding layer arranged between supply lines and electrodes to minimize residual electrical fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a piezoelectric layer with electrode arrangements is used for adaptive mirror deformation, then imaging errors can be compensated, but unwanted electric fields from supply lines cause uncontrollable mirror deformation
Solution Approach 1:
A shielding layer made of electrically conductive material is introduced as an intermediary between the electrode supply lines and the piezoelectric layer. This shielding layer absorbs or redirects the unwanted electric fields generated by the supply lines, preventing them from acting on the piezoelectric layer and causing uncontrollable deformation, while allowing the controlled electric fields from electrodes to still achieve the desired piezoelectric effect for imaging error compensation.
2Adaptability or versatility
If materials with different thermal expansion coefficients are used in the mirror structure, then functional layers can be integrated, but thermal expansion differences cause mirror surface deformation
Solution Approach 1:
The patent applies the thermal expansion principle by selecting materials for different layers (mirror substrate, piezoelectric layer, electrode arrangements, shielding layer) with carefully matched thermal expansion coefficients. This material selection strategy ensures that when the mirror is heated during EUV operation, all layers expand at similar rates, preventing differential thermal expansion from causing the electrode structure to emboss into the optical surface and maintaining mirror shape stability.
3Reliability
If EUV radiation is absorbed by the mirror, then the mirror can be used for imaging, but heating and thermal deformation occur
Solution Approach 1:
The patent employs parameter changes by selecting materials with appropriate thermal and optical properties for each layer. The mirror substrate material (such as TiO2-doped quartz glass or Zerodur) is chosen for its low thermal expansion coefficient and good EUV reflectivity. The piezoelectric layer and other functional layers are selected to have thermal expansion coefficients matched to the substrate, ensuring that thermal deformation is minimized while maintaining imaging functionality under EUV radiation heating conditions.
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 shields unwanted electric fields and compensates for thermal expansion variations, enabling precise deformation control and improved imaging quality by reducing aberrations and maintaining the desired piezoelectric effect, thus enhancing the performance of EUV mirrors in microlithographic systems.
Implementation Method 1
a piezoelectric layer, which is arranged between a mirror substrate (12) and a reflection layer stack (21) and via a first electrode arrangement (14) located on the side of the piezoelectric layer (16) facing the reflection layer stack (21) and a second electrode arrangement (20) located on the side of the piezoelectric layer (16) facing the mirror substrate (12), with an electric field for generating a locally variable deformation can be acted upon
Implementation Method 2
a shielding layer for shielding an electric field generated by said leads (19a, 19b, 19c, ...) from said piezoelectric layer (16)
Implementation Method 3
a mediator layer made of a material with an electrical conductivity of less than 200 Siemens/meter (S/m) is also arranged between the piezoelectric layer and the electrode arrangement having the plurality of electrodes
Implementation Method 4
the EUV mirrors experience heating, in particular as a result of the absorption of the radiation emitted by the EUV light source, and an associated thermal expansion or deformation
Data Source
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AI summary
The invention relates to a mirror, in particular for a microlithographic projection exposure apparatus. A mirror (10, 30) according to the invention comprises an optical active surface (11, 31), a mirror substrate (12, 32), a reflection layer stack (21, 41) for reflecting electromagnetic radiation incident on the optical active surface, and at least one piezoelectric layer (16, 36) which is arranged between the mirror substrate and the reflection layer stack and which can be applied by an electric field in order to create a locally variable deformation, via a first electrode arrangement (20, 40) located on the side of the piezoelectric layer facing the reflection layer stack, and a second electrode arrangement (14, 34), located on the side of the piezoelectric layer facing the mirror substrate, wherein the first electrode arrangement and/or the second electrode arrangement comprises a plurality of electrodes (20a, 20b, 20c,..., 40a, 40b, 40c,... ), which can each be applied via a line (19a, 19b, 19c,..., 39a, 39b, 39c,... ) with an electrical voltage with respect to the respective other electrode arrangement, wherein a shielding layer (22, 42) made from electrically conductive material is further arranged in such a way as to at least partially shield the piezoelectric layer from the electrical field generated by said lines.