EUV Collector Mirror Contamination Prevention via Nanoscale Debris Control
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Solution Overview
Problem
Current methods for preventing contamination of EUV collector mirrors in EUV light source apparatuses are ineffective in preventing large debris particles from adhering, leading to reduced mirror reflectance and increased maintenance costs, as they either fail to ionize neutral particles or require frequent cleaning of debris shields.
Innovation Solution
Using solid tin as the target and a CO2 laser to reduce debris size to nanometer or smaller sizes, and employing methods such as background gas supply, gas flow, electrical charging, magnetic fields, electric fields, or heating to prevent these smaller debris particles from reaching the optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods (debris shields, background gas) are used to prevent contamination, then some contamination is reduced, but large debris particles still adhere to mirrors causing reflectance degradation and frequent maintenance
Solution Approach 1:
The invention changes the size parameter of debris particles from microscale to nanoscale by using solid tin targets with CO2 laser irradiation. This parameter change makes particles susceptible to different control mechanisms (background gas, electric fields, magnetic fields) that can effectively prevent their deposition on optical elements, thereby resolving the contradiction between maintaining mirror reflectance and reducing maintenance frequency
Solution Approach 2:
The invention replaces mechanical debris shield systems with non-mechanical control methods including background gas supply, electric field generation, and magnetic field generation. These substitution methods more effectively prevent nanosize debris from reaching optical elements, eliminating the need for frequent mechanical shield cleaning and maintaining mirror performance over extended periods
2Object-affected harmful factors
If debris shields are used to block scattered material, then contamination is partially prevented, but the shields themselves require frequent cleaning and maintenance
Solution Approach 1:
The invention extracts the harmful function from the debris shield system by removing the shields entirely and replacing them with background gas, electric field, and magnetic field mechanisms. This extraction eliminates the maintenance burden associated with cleaning shields while continuing to prevent debris adhesion to optical elements through the alternative mechanisms
Solution Approach 2:
The invention substitutes the mechanical debris shield system with non-mechanical fields (background gas, electric fields, magnetic fields) that passively prevent debris adhesion without requiring active maintenance or cleaning operations, thereby resolving the contradiction between preventing contamination and maintaining shield cleanliness
3Adaptability or versatility
If neutral particles are not ionized, then they pass through fields unchanged, but they still adhere to optical elements causing contamination
Solution Approach 1:
The invention changes the charge state parameter of neutral particles by ionizing them through plasma generation in the vacuum chamber. This parameter change enables subsequent control of particles using electric and magnetic fields, providing flexible control over particle trajectories while preventing adhesion to optical elements
Solution Approach 2:
The invention performs preliminary ionization of neutral particles during the plasma generation phase before they can adhere to optical elements. This preliminary action enables subsequent field-based control mechanisms to effectively manipulate particle trajectories, resolving the contradiction between particle control flexibility and preventing neutral particle adhesion
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
Effectively extends the service life of EUV collector mirrors by preventing the formation of metal films, reducing maintenance costs, and maintaining high reflectance levels by controlling and preventing nanosize debris from adhering to the mirrors.
Implementation Method 1
irradiating a target with a laser beam, the target substance is excited and converted into plasma
Implementation Method 2
decreasing the size of the scattered material emitted from the plasma to a nanometer or smaller size by using solid tin as the target and using a CO2 laser as an excitation source
Implementation Method 3
background gas supply means for supplying into the chamber background gas that prevents the nanosize scattered material from reaching the optical element
Implementation Method 4
electric field formation means for generating inside the chamber an electric field that prevents the charged nanosize scattered material from reaching the optical element
Implementation Method 5
magnetic field formation means for generating inside the chamber a magnetic field that prevents the charged nanosize scattered material from reaching the optical element
Implementation Method 6
heating means for evaporating (causing diffusion based on thermal motion) the nanosize scattered material
Data Source
AI summary
Solid tin (Sn) is used as a target, a CO2 laser is used as an excitation source for the target, and after the size of debris emitted from plasma is decreased to a nanometer or smaller size by exciting the solid tin by a laser beam outputted from the CO2 laser, the emitted debris of a nanometer or smaller size is acted upon so as not to reach the optical element. In accordance with the present invention, in the EUV light source apparatus, the debris emitted together with EUV light from plasma generated by exciting a target within a chamber by a laser beam is prevented from adhering to an optical element provided within the chamber and forming a metal film. As a result, the service life of the optical element can be extended.