Mesh Spectrum Purity Filter for EUV Light Source
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Solution Overview
Problem
Conventional EUV light source apparatuses face issues with low output efficiency, structural integrity, and exposure uniformity due to the inefficiency of spectrum purity filters in blocking CO2 laser beams and maintaining EUV light purity, particularly at 13.5 nm wavelength, which affects semiconductor microfabrication processes.
Innovation Solution
The implementation of a mesh-type spectrum purity filter with apertures having a pitch not larger than half the wavelength of the CO2 laser beam, coated with conductive materials like gold or molybdenum, to effectively transmit EUV light while reflecting the CO2 laser beam, thereby enhancing spectrum purity and reducing the risk of filter deformation and breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional spectrum purity filter is used to block CO2 laser beam, then the EUV light purity is improved, but the filter structure deforms and breaks due to thermal expansion from absorbed infrared light
Solution Approach 1:
The patent changes the material parameter of the filter from conventional materials to a material with a specific band gap energy (3.4-4.0 eV) that is larger than the CO2 laser photon energy (0.12 eV). This parameter change allows the filter to block infrared light while maintaining structural integrity, as the material does not absorb the CO2 laser wavelength and thus does not undergo thermal expansion.
Solution Approach 2:
The patent employs a composite filtering approach by combining a first filter for EUV wavelength selection with a second filter having specific band gap properties for CO2 laser blocking. This composite material strategy allows each filter to specialize in one function, with the second filter specifically designed to prevent thermal deformation from CO2 laser absorption.
2Manufacturing precision
If a spectrum purity filter is used to remove unnecessary wavelength components, then the EUV exposure contrast is improved, but the CO2 laser beam is not effectively blocked causing thermal expansion in optical parts
Solution Approach 1:
The patent changes the optical parameter of the filter material by selecting materials with band gap energies (3.4-4.0 eV) that exceed the CO2 laser photon energy (0.12 eV). This parameter selection ensures the material is transparent to CO2 laser infrared light, allowing the laser beam to pass through without absorption and subsequent thermal expansion of optical components.
Solution Approach 2:
The patent introduces a second filter as an intermediary component between the plasma generation chamber and the exposure apparatus. This intermediary filter specifically addresses the CO2 laser beam by allowing it to pass through without absorption, thereby preventing thermal expansion in downstream optical parts while the first filter handles EUV wavelength selection.
3Reliability
If a thin film filter is used to prevent Sn debris contamination, then the exposure unit is protected, but the filter absorbs CO2 laser light causing thermal deformation
Solution Approach 1:
The patent changes the material composition parameter of the second filter to materials (Zr, Si, or ZrSi2) with high EUV transmittance and appropriate band gap energies. These material parameters ensure high transparency to both EUV light and CO2 laser infrared light, preventing thermal deformation while maintaining protection functions.
Solution Approach 2:
The patent uses composite material strategy by selecting from multiple material options (Zr, Si, ZrSi2) that combine high EUV transmittance with appropriate optical properties for CO2 laser transparency. This composite approach allows optimization of both contamination protection and thermal stability simultaneously.
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 significantly improves the output efficiency and spectral purity of EUV light, maintaining the structural integrity of the filter and ensuring uniform exposure, crucial for advanced semiconductor microfabrication processes beyond 32 nm.
Implementation Method 1
a mesh 22a in which an arrangement of apertures is formed, for transmitting the extreme ultraviolet light and reflecting the CO2 laser beam
Implementation Method 2
the mesh 22a is formed of a material having electrical conductivity, or is formed by coating a material having electrical conductivity on at least a light incident surface
Data Source
AI summary
An extreme ultraviolet light source apparatus using a spectrum purity filter capable of obtaining EUV light with high spectrum purity. The apparatus includes a chamber; a target supply unit for supplying a target material; a driver laser using a laser gas containing a carbon dioxide gas as a laser medium, for applying a laser beam to the target material to generate plasma; a collector mirror for collecting and outputting the extreme ultraviolet light radiated from the plasma; and a spectrum purity filter provided in an optical path of the extreme ultraviolet light, for transmitting the extreme ultraviolet light and reflecting the laser beam, the spectrum purity filter including a mesh having electrical conductivity and formed with an arrangement of apertures having a pitch not larger than a half of a shortest wavelength of the laser beam applied by the driver laser.