Deformable Mirror Piezoelectric Column Segmentation
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Solution Overview
Problem
Microlithography projection exposure apparatuses face challenges in achieving sufficiently large deflections with high setting accuracy due to the indentation effect of piezoelectric layers into mirror substrates and hysteresis effects in adaptive mirrors, particularly in the EUV range.
Innovation Solution
A deformable mirror design with a piezoelectric layer composed of columns with a specific mean column diameter and spacing, and varying column diameters in different regions to minimize indentation and hysteresis, along with a method to compensate for hysteresis contributions by applying a modified voltage distribution and aligning Weiss domains using a unipolar alternating electric field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a piezoelectric layer is applied to the mirror substrate to enable adaptive deformation, then imaging aberrations can be compensated, but the piezoelectric layer indents into the mirror substrate due to lateral contraction, reducing the total figure effect
Solution Approach 1:
The piezoelectric layer is segmented into multiple discrete columns rather than being continuous. This segmentation allows each column to expand independently in the vertical direction without generating lateral contraction stresses that would cause indentation into the mirror substrate, thereby preserving the total figure effect while maintaining aberration compensation capability.
Solution Approach 2:
The piezoelectric layer is structured with columns having different diameters in different regions of the mirror surface. This local variation in column geometry allows optimization of the deformation characteristics in different areas, enabling precise control of the mirror figure while avoiding indentation issues.
2Manufacturing precision
If a continuous piezoelectric layer is used for adaptive mirror deformation, then optical aberrations can be corrected, but hysteresis effects limit the setting accuracy
Solution Approach 1:
Dividing the piezoelectric layer into discrete columns reduces hysteresis effects by eliminating the lateral contraction and friction that occur in continuous layers during deformation cycles. Each column can deform more independently and reversibly, improving the repeatability and accuracy of the mirror surface positioning.
Solution Approach 2:
By changing the physical structure of the piezoelectric layer from continuous to discrete columns, and by varying column diameters across different regions, the deformation characteristics and hysteresis behavior are optimized to achieve higher setting accuracy while maintaining aberration correction capability.
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 enables larger deflections with improved setting accuracy by reducing mechanical stress and friction-related errors, enhancing the overall performance of adaptive mirrors in microlithography projection exposure systems.
Implementation Method 1
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 unipolar alternating electric field is generated along the direction of the surface normal to the optical effective surface before the mirror is started up or/and during at least one operating pause for the purpose of aligning Weiss domains in the piezoelectric layer
Data Source
AI summary
A mirror for a microlithographic projection exposure apparatus, and a method for operating a deformable mirror. In one aspect, a mirror includes an optical effective surface (11), a mirror substrate (12), a reflection layer stack (21) for reflecting electromagnetic radiation incident on the optical effective surface, and at least one piezoelectric layer (16) arranged between the mirror substrate and the reflection layer stack and to which an electric field for producing a locally variable deformation is able to be applied by a first electrode arrangement situated on the side of the piezoelectric layer (16) facing the reflection layer stack, and by a second electrode arrangement situated on the side of the piezoelectric layer facing the mirror substrate. The piezoelectric layer has a plurality of columns spatially separated from one another by column boundaries, wherein a mean column diameter of the columns is in the range of 0.1 μm to 50 μm.