Two-Step Gas Cleaning for EUV Optical Surfaces
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Solution Overview
Problem
Current methods for cleaning optical surfaces in EUV-radiation units are inadequate in removing contaminations, particularly non-volatile substances, which reduce the optical quality and lifetime of components due to incomplete conversion into volatile compounds during the cleaning process.
Innovation Solution
A method involving a pretreatment step with a second gas or gas mixture that forms highly volatile compounds with contaminations, followed by a cleaning step using a first gas or gas mixture, utilizing reducing gases and radical generation techniques such as hot surfaces or discharges to enhance contamination removal, and employing inert materials and flow control to maintain radical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-step cleaning process using a first gas is applied to remove contaminations from optical surfaces, then some contaminations are removed by forming volatile compounds, but non-volatile substances remain as residues reducing cleaning effectiveness
Solution Approach 1:
The invention applies a preliminary action by introducing a second gas (oxygen or oxygen-containing gas) before the first gas (hydrogen or hydrogen-containing gas) in a two-step cleaning process. The second gas oxidizes non-volatile contaminations into volatile compounds that can then be effectively removed by the subsequent first gas, preventing residue formation and improving overall cleaning effectiveness.
2Manufacturing precision
If cleaning gases are introduced to remove contaminations, then the optical quality is improved, but the process time and complexity increase due to multiple gas introduction steps
Solution Approach 1:
The cleaning process uses preliminary action by sequentially introducing a second gas (oxygen-containing) followed by a first gas (hydrogen-containing) to achieve effective contamination removal. This two-step approach systematically addresses different types of contaminations while maintaining manageable process complexity through clear sequential steps.
Solution Approach 2:
The invention changes the chemical parameters of the cleaning environment by switching between different gas compositions (oxygen-containing then hydrogen-containing). This parameter change enables the conversion of non-volatile contaminations into volatile forms, improving optical quality without requiring complex mechanical or thermal processing systems.
3Loss of substance
If hydrogen-containing gas is used to form volatile compounds with contaminations, then volatile contaminations are removed effectively, but non-volatile substances do not react and remain on the surface
Solution Approach 1:
The invention changes the chemical reactivity parameter by introducing an oxygen-containing gas before the hydrogen-containing gas. This parameter change transforms non-volatile contaminations into oxidized forms that can then react with hydrogen to form volatile compounds, achieving complete contamination removal including previously non-reactive substances.
Solution Approach 2:
The oxygen-containing gas acts as an intermediary that first reacts with non-volatile contaminations to create intermediate oxidized products. These intermediates then serve as reactants for the subsequent hydrogen-containing gas, enabling complete volatilization and removal of all contamination types through this two-stage intermediary process.
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
Significantly increases the portion of contaminations removed, achieving a high degree of cleaning and extending the lifetime of optical components with timely and spatially homogeneous imaging, while maintaining the optical quality of EUV irradiation systems.
Implementation Method 1
a second gas or gas mixture, called pretreatment gas, is brought into contact with the optical surfaces, wherein the second gas or gas mixture is selected to react with a second portion of the contaminations different from the first portion to form a reaction product
Implementation Method 2
a first gas or gas mixture, called cleaning gas, is brought into contact with the optical surfaces thereby forming a volatile compound with a first portion of the contaminations
Implementation Method 3
By additionally irradiating these gases with UV or EUV-radiation, radicals are generated which enhance the reaction rates with the contaminations
Implementation Method 4
utilizing reducing gases and radical generation techniques such as hot surfaces or discharges to enhance contamination removal
Data Source
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AI summary
The present invention provides a method of cleaning optical surfaces in an irradiation unit in order to remove contaminations deposited on said optical surfaces. The method includes a cleaning step in which a first gas or gas mixture is brought into contact with said optical surfaces thereby forming a volatile compound with a first portion of said contaminations. In an operation pause of the irradiation unit prior to the cleaning step, a pretreatment step is performed, in which a second gas or gas mixture is brought into contact with said optical surfaces. Said second gas or gas mixture is selected to react with a second portion of said contaminations different from said first portion to form a reaction product, which is able to form a volatile compound with said first gas or gas mixture.