Atomic Layer Etching for EUV Mirror Contamination Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for removing contamination layers from EUV mirrors in lithography systems are inefficient, leading to transmittance losses and imaging errors due to the strong adhesion of elements like Zn, Sn, and Si, which cannot be effectively removed by conventional cleaning with atomic hydrogen, and result in over-cleaning or alloy formation with the capping layer.
Innovation Solution
An atomic layer etching process is employed, involving a surface modification step using oxidizing agents like oxygen and a material detachment step with hydrogen radicals or ions, allowing for controlled removal of contamination layers without damaging the reflective coating, using a sequence of alternating gas streams and plasma-assisted etching to detach oxidized material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If atomic hydrogen cleaning is used to remove contamination layers from EUV mirrors, then some contaminations can be removed, but over-cleaning occurs causing blister formation and delamination of the reflective coating
Solution Approach 1:
The patent applies preliminary action by first oxidizing the contamination layer (particularly Sn) to form metal oxides before removal. This oxidation step modifies the contamination to make it more susceptible to subsequent removal processes while being less aggressive to the underlying reflective coating, thus preventing over-cleaning damage
Solution Approach 2:
The patent uses oxygen as an intermediary substance that mediates between the contamination layer and the removal process. The oxygen oxidizes the contamination layer to form metal oxides, which then serve as an intermediate state that is easier to remove selectively without damaging the reflective coating
2Manufacturing precision
If atomic hydrogen cleaning is used to remove contamination layers, then cleaning action is provided, but alloy formation with the capping layer occurs making contaminations irre removable
Solution Approach 1:
The patent applies preliminary action by oxidizing the contamination layer to form metal oxides before removal. This oxidation step modifies the contamination to make it more susceptible to subsequent removal processes while being less aggressive to the underlying reflective coating, thus preventing over-cleaning damage
Solution Approach 2:
The patent changes the chemical state of the contamination layer from metallic to oxidized form through controlled oxidation. This parameter change (from metal to metal oxide) alters the properties of the contamination to enable selective removal while preserving the capping layer composition
3Ease of operation
If conventional cleaning methods are used, then simple cleaning action is provided, but strongly adherent elements like Zn, Sn, and Si cannot be effectively removed
Solution Approach 1:
The patent applies preliminary action by oxidizing the contamination layer (particularly Sn) to form metal oxides before removal. This oxidation step modifies the contamination to make it more susceptible to subsequent removal processes while being less aggressive to the underlying reflective coating, thus preventing over-cleaning damage
Solution Approach 2:
The patent uses oxygen or other oxidizing agents to accelerate the oxidation of strongly adherent elements like Zn, Sn, and Si in the contamination layer. This accelerated oxidation converts these difficult-to-remove elements into metal oxides that can be more effectively removed in subsequent steps
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 method effectively removes strongly adherent contamination layers with minimal damage to the optical element, maintaining reflectance and preventing delamination, enabling the reuse of reflective optical elements by completely stripping off contaminants, thus improving system performance and extending the lifespan of EUV mirrors.
Implementation Method 1
oxidizing the contamination layer to form metal oxides
Implementation Method 2
detaching the oxidized contamination layer from the optical surface with hydrogen radicals or hydrogen ions
Implementation Method 3
plasma-assisted etching to detach oxidized material
Data Source
AI summary
A method for at least partially removing a contamination layer (24) from an optical surface (14a) of an optical element (14) that reflects EUV radiation includes: performing an atomic layer etching process for at least partially removing the contamination layer (24) from the optical surface (14a), which, in turn, includes: exposing the contamination layer (24) to a surface-modifying reactant (44) in a surface modification step, and exposing the contamination layer (24) to a material-detaching reactant (45) in a material detachment step. The optical element (14) is typically taken, before the atomic layer etching process is performed, from an optical arrangement, in particular from an EUV lithography system, in which the optical surface (14a) of the optical element (14) is exposed to EUV radiation (6), during which the contamination layer (24) is formed.