EUV Mirror Doping for Structural Stability
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Solution Overview
Problem
Mirrors for the EUV wavelength range in projection exposure apparatuses for microlithography suffer from absorption of EUV photons leading to destabilized atoms, causing structural changes, increased layer stress, surface roughness, and optical property alterations, resulting in image aberrations and stray light losses over time.
Innovation Solution
A mirror with a substrate and layer arrangement featuring non-metallic individual layers doped with impurity atoms to enhance charge carrier density and electrical conductivity, stabilizing atoms by providing freely mobile electrons, thereby reducing structural changes and thermal loading, and incorporating specific materials and layer subsystems for high reflectivity and stress compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If mirrors with high reflectivity are used in EUV projection exposure apparatus, then the total transmission and light power utilization are improved, but the mirrors absorb EUV photons causing structural changes, layer stress changes, and surface roughness increases over time
Solution Approach 1:
The patent applies parameter changes by doping non-metallic individual layers with impurity atoms to achieve specific charge carrier densities (>6×10^10 cm^-3) and electrical conductivities (>1×10^-3 S/m). This transforms the physical parameters of the layer materials to stabilize atoms against EUV-induced destabilization while maintaining optical properties
Solution Approach 2:
The patent uses composite materials by combining non-metallic individual layers (such as silicon oxide, silicon nitride, or silicon carbide) with specific impurity atom dopants. This creates a composite structure that provides both the necessary optical properties for high reflectivity and the electrical conductivity needed to stabilize atoms against EUV radiation damage
2Stability of the object's composition
If non-metallic individual layers are doped with impurity atoms to increase charge carrier density, then atom stabilization and long-term spectral stability are improved, but the manufacturing complexity and doping precision requirements increase
Solution Approach 1:
The patent specifies concrete parameter ranges for doping (impurity atom concentrations of 10 ppb to 10%, charge carrier densities >6×10^10 cm^-3, electrical conductivities >1×10^-3 S/m) that transform the manufacturing approach from qualitative to quantitative, enabling standardized production processes with controlled precision requirements
Solution Approach 2:
The patent introduces impurity atoms as intermediary elements that mediate between the EUV radiation environment and the non-metallic layer structure. These dopant atoms act as charge carriers that stabilize the layer structure without fundamentally altering the material's optical properties, serving as a buffer against radiation-induced changes
3Shape
If buffer layers or anti-stress layers are applied to compensate layer stress, then the mirror shape stability is improved, but the device complexity and number of layers increase
Solution Approach 1:
The patent makes the non-metallic individual layers multi-functional by doping them to simultaneously provide structural stabilization against EUV radiation and stress compensation. This eliminates the need for separate buffer or anti-stress layers, as the doped layers perform both optical and mechanical functions
Solution Approach 2:
The patent extracts the stress compensation function from separate buffer/anti-stress layers and integrates it directly into the non-metallic individual layers through doping. This removes unnecessary layers from the structure, simplifying the overall device while maintaining shape stability
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 doped mirror achieves long-term stability in spectral behavior, surface shape, and reduced stray light losses, maintaining high reflectivity and preventing spectral shifts, ensuring consistent optical properties and reduced layer stress, thus minimizing image aberrations and transmission losses.
Implementation Method 1
the absorption of the high-energy EUV photons takes place by way of the photoelectric effect, electrons in the solid being ejected
Implementation Method 2
an electrical conductivity of greater than 1×10^-3 S/m, in particular an electrical conductivity of greater than 1 S/m, are afforded for the non-metallic individual layer
Data Source
AI summary
A mirror (1) for the EUV wavelength range having a reflectivity of greater than 40% for at least one angle of incidence of between 0° and 25° includes a substrate (S) and a layer arrangement, wherein the layer arrangement has at least one non-metallic individual layer (B, H, M), and wherein the non-metallic individual layer (B, H, M) has a doping with impurity atoms of between 10 ppb and 10%, in particular between 100 ppb and 0.1%, providing the non-metallic individual layer (B, H, M) with a charge carrier density of greater than 6*1010 cm−3 and/or an electrical conductivity of greater than 1*10−3 S/m, in particular with a charge carrier density of greater than 6*1013 cm−3 and/or an electrical conductivity of greater than 1 S/m.