EUV Lithography Optical Element Stress-Balanced Conductive Coating
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Solution Overview
Problem
The use of a single-layer electrically conductive coating with high tensile stress in optical elements for EUV lithography can cause deformation and optical aberrations due to layer stresses, potentially degrading the optical properties of the reflective coating.
Innovation Solution
Employing an electrically conductive coating with a combination of a first layer under tensile stress and a second layer under compressive stress, where the materials and thicknesses are chosen to compensate each other, thereby reducing substrate deformation and maintaining the optical integrity of the reflective surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer electrically conductive coating is used to ground the optical element, then electrical conductivity is improved, but substrate deformation and optical aberrations occur due to layer stress
Solution Approach 1:
The electrically conductive coating is segmented into multiple layers (first conductive layer and second conductive layer) with different stress characteristics. The first layer provides electrical conductivity while the second layer compensates for stress-induced deformation, resolving the contradiction between conductivity and surface accuracy.
Solution Approach 2:
The patent uses a composite structure of multiple conductive layers with different material properties. The first layer (e.g., gold) provides high conductivity, while the second layer (e.g., chromium) provides compressive stress to counterbalance the tensile stress of the first layer, maintaining both electrical performance and optical precision.
2Reliability
If a thick electrically conductive coating is applied to ensure conductivity, then electrical grounding is improved, but substrate curvature increases due to accumulated layer stress
Solution Approach 1:
The second conductive layer acts as a counterweight to the stress generated by the first layer. By applying a layer with opposite stress characteristics (compressive vs. tensile), the net stress on the substrate is reduced, preventing curvature while maintaining the electrical grounding function.
Solution Approach 2:
The patent changes the parameters of the conductive coating system by introducing multiple layers with different thicknesses, materials, and stress characteristics. This allows independent optimization of electrical conductivity (through total thickness and material choice) and surface shape (through stress balancing).
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 minimizes optical aberrations and maintains the optical properties of the reflective coating by effectively balancing layer stresses, allowing for precise control of the resulting stress in the conductive coating to prevent substrate curvature and ensure accurate EUV radiation reflection.
Implementation Method 1
the electrically conductive coating has at least a first layer which is under tensile stress and at least a second layer which is under compressive stress
Data Source
Figure 1
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AI summary
The invention relates to an optical element (14), in particular for EUV lithography, comprising a substrate (15), a reflective coating (16) applied to the substrate (15), and an electrically conductive coating (19) extending between the substrate (15) and the reflective coating (16), and having at least one first layer (22a) under tensile stress and at least one second layer (22b) under compressive stress. The electrically conductive coating (19) has at least one section (20) that extends laterally beyond the reflective coating (16) on the substrate (15). The invention also relates to an optical assembly, in particular an EUV lithography system, comprising at least one optical element (14) of this type.