EUV Optical Surface Cleaning via Volatile Compound Formation
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Solution Overview
Problem
In EUV-lithography systems, contaminations from radiation sources, such as metallic substances and debris, deposit on optical components, reducing optical quality and requiring frequent cleaning to maintain imaging quality and extend component lifetime, with existing methods struggling to achieve significant debris mitigation between the radiation source and collector mirror.
Innovation Solution
A method involving a cleaning step where a gas or gas mixture forms volatile compounds with contaminations on optical surfaces, followed by an after-treatment step where the radiation source is used to release residues, and a separation of volumes to pump out desorbed compounds, along with optional use of additional gases to support residue release and form protective layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gas discharge plasma or laser plasma is used to generate EUV radiation, then radiation intensity is improved, but debris and contaminations are generated that deposit on optical components
Solution Approach 1:
The patent extracts and removes debris and contaminations from the optical system by introducing a cleaning gas that reacts with deposited materials to form volatile compounds, which are then pumped away. This separates the harmful byproducts from the optical components while maintaining the plasma radiation source.
Solution Approach 2:
The patent introduces a cleaning gas as an intermediary substance that mediates between the debris/contaminations on optical surfaces and the vacuum pumping system. The cleaning gas reacts with contaminations to form volatile compounds that can be easily removed, acting as a bridge to eliminate harmful deposits without affecting the plasma source operation.
2Manufacturing precision
If cleaning is performed frequently to remove contaminations, then optical quality is maintained, but system downtime and operational complexity increase
Solution Approach 1:
The patent enables continuous cleaning action by introducing the cleaning gas during normal operation without requiring system shutdown. The cleaning process occurs continuously as the plasma operates, maintaining optical quality without interrupting the radiation generation and eliminating downtime associated with traditional cleaning methods.
Solution Approach 2:
The patent implements self-service cleaning where the system cleans itself during operation. The cleaning gas is introduced into the existing vacuum system and automatically reacts with contaminations on optical surfaces, with the volatile reaction products being pumped away by the existing vacuum pumps, requiring no external intervention or system shutdown.
3Object-generated harmful factors
If cleaning gas is introduced to form volatile compounds with contaminations, then contaminations are removed, but residues may remain on optical surfaces
Solution Approach 1:
The patent changes the chemical parameters of the cleaning process by selecting specific cleaning gases (such as fluorinated compounds or oxygen-containing gases) that react with contaminations to form highly volatile compounds with low residue formation. By adjusting the chemical composition and reactivity parameters of the cleaning gas, complete removal of contaminations is achieved without leaving residues on optical surfaces.
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 inorganic contaminations, maintains spatial homogeneity, and extends the lifetime of optical components by ensuring thorough cleaning and reducing absorption losses, allowing for timely and homogeneous EUV-illumination.
Implementation Method 1
a first gas or gas mixture is brought into contact with said optical surfaces, thereby forming volatile compounds with contaminations deposited on said optical surfaces
Implementation Method 2
the radiation source is operated once or several times in order to release residues of the cleaning step from the optical surfaces by irradiating said optical surfaces with said EUV-radiation or soft X-rays
Implementation Method 3
said compounds are pumped out of the first volume together with the first gas or gas mixture
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The present invention relates to a method of cleaning and after treatment of optical surfaces in an irradiation unit, said irradiation unit comprising a radiation source (1, 31) emitting EUV-radiation and/or soft X-rays, a first volume (40) following said radiation source (1, 31) and containing first optical components (3, 33) with said optical surfaces, and a second volume (41) following said first volume (40) and containing second optical components (38). The method comprises at least one cleaning step in which a first gas or gas mixture is brought into contact with said optical surfaces, thereby forming volatile compounds with contaminations deposited on said optical surfaces, wherein said compounds are pumped out of the first volume (40) together with the first gas or gas mixture. In an after treatment step following said cleaning step the radiation source (1, 31) is operated once or several times in order to release residues of the cleaning step from the optical surfaces by irradiating said optical surfaces with said EUV-radiation or soft X-rays while the first volume (40) is separated from the second volume (41), wherein said released residues are pumped out of the first volume (40). With this method an improved cleaning result is achieved.