In-situ Repair of EUV Multilayer Mirrors Using Ion Sputtering
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Solution Overview
Problem
Optical elements in vacuum chambers used for generating extreme ultraviolet radiation suffer from contamination and wear, leading to reduced reflectivity and lifetime, as they are exposed to high-energy ions and reactive source materials, necessitating a method to clean and repair surfaces in-situ without removing the elements from the environment.
Innovation Solution
A method involving in-situ cleaning using hydrogen radicals to remove contaminants followed by exposing the surface to an ion flux from an ion gun to repair damaged areas, effectively removing source material and restoring the optical element's surface, thereby extending its lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical element is placed within the vacuum chamber with the plasma to collect and redirect EUV light, then the optical element can perform its function in the EUV environment, but the optical element's surface becomes contaminated and damaged by high energy ions and source material particles, reducing reflectivity and lifetime
Solution Approach 1:
The patent applies ion bombardment, which is typically a harmful process causing surface damage, to achieve the beneficial effect of removing contaminated source material from the optical element surface. The ion flux sputters away carbon-containing contaminants and damaged collector material, converting the harmful ion interaction into a useful cleaning and repair mechanism that restores surface reflectivity
Solution Approach 2:
The patent introduces hydrogen radicals as an intermediary substance to facilitate the removal of carbon-containing contaminants from the optical element surface. The hydrogen radicals react with carbon contaminants to form volatile hydrocarbon species that can be pumped away, serving as a chemical mediator that enables contaminant removal without direct mechanical contact
2Duration of action of stationary object
If protective layers or intermediate diffusion barrier layers are used to isolate the MLM layers from the environment, then the optical element lifetime is extended, but the device complexity and manufacturing complexity increase
Solution Approach 1:
The patent implements a self-service mechanism where the optical element cleans and repairs itself through in-situ ion bombardment and hydrogen radical treatment. The optical element uses the plasma environment and ion flux to automatically remove contaminants and damaged material from its own surface, eliminating the need for external protective layers or manual maintenance interventions
Solution Approach 2:
The patent applies the discarding and recovering principle by continuously removing damaged collector material and contaminants from the optical element surface through ion sputtering and hydrogen radical cleaning. This ongoing removal and restoration process recovers surface reflectivity and extends optical element lifetime without requiring protective coatings or complex structural modifications
3Object-affected harmful factors
If the collector is heated to an elevated temperature to evaporate debris from its surface, then contaminant removal is achieved, but energy consumption increases and the collector material may be damaged by thermal stress
Solution Approach 1:
The patent replaces the thermal evaporation process with a mechanical sputtering process using ion bombardment. Instead of using thermal energy to evaporate contaminants, the patent uses kinetic energy from ion particles to physically sputter away contaminants and damaged material, substituting a mechanical removal mechanism for a thermal one and reducing overall energy consumption
Solution Approach 2:
The patent changes the removal mechanism parameter from thermal evaporation to ion-induced sputtering. By switching from a thermally-driven process to a kinetically-driven process, the patent achieves contaminant removal at lower energy input and without the thermal stress damage that would occur with high-temperature heating
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 significantly extends the lifetime of optical elements by removing contaminants and repairing damaged surfaces within the vacuum chamber, maintaining reflectivity and reducing downtime and replacement costs.
Implementation Method 1
cleaning the exposed surface while in the vacuum chamber with hydrogen radicals
Implementation Method 2
exposing the cleaned exposed surface while in the vacuum chamber to an ion flux to remove at least some areas of the surface that have been damaged
Data Source
AI summary
Method of and apparatus for repairing an optical element disposed in a vacuum chamber while the optical element is in the vacuum chamber. An exposed surface of the optical element is exposed to an ion flux generated by an ion source to remove at least some areas of the surface that have been damaged by exposure to the environment within the vacuum chamber. The method and apparatus are especially applicable to repair multilayer mirrors serving as collectors in systems for generating EUV light for use in semiconductor photolithography.