EUV Mirror Decontamination via Hydrogen Radical Generation
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Solution Overview
Problem
In EUV lithography, tin compounds accumulate on mirrors, reducing reflectivity and causing damage, due to the emission of tin fragments during the ablation process, which existing technologies fail to effectively remove.
Innovation Solution
An exposure apparatus and decontamination apparatus that utilize a pulsed laser to generate hydrogen radicals within a vacuum chamber, where the conditions for laser irradiation and droplet supply are adjusted during cleaning to efficiently react and remove tin compounds as SnH4, using a combination of EUV and VUV lasers and hydrogen gas flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a pulsed laser ablates a tin droplet target to generate EUV light, then EUV light is produced for lithography, but tin fragments accumulate on the condensing mirror surface reducing reflectivity
Solution Approach 1:
The patent converts the harmful tin fragments that accumulate on the mirror into beneficial hydrogen tin radicals (SnHx) by introducing hydrogen gas and using laser ablation to create plasma. The tin fragments react with hydrogen to form volatile SnHx compounds that can be removed, thus transforming the contamination problem into a cleaning mechanism
Solution Approach 2:
Hydrogen gas is introduced as an intermediary substance between the tin target and the condensing mirror. The hydrogen reacts with tin fragments to form hydrogen tin radicals that are more easily removed than pure tin deposits, serving as a mediating chemical that facilitates cleaner mirror surfaces
2Reliability
If cleaning conditions are applied to remove tin compounds, then mirror reflectivity is restored, but exposure operation conditions cannot be maintained
Solution Approach 1:
The system alternates between exposure operation mode and cleaning mode in periodic cycles. During exposure, EUV light is generated for lithography; during cleaning intervals, hydrogen gas is introduced and laser parameters are adjusted to generate hydrogen tin radicals for mirror cleaning. This periodic switching allows both functions to be performed without compromising either
Solution Approach 2:
The system dynamically adjusts laser parameters (wavelength, pulse duration, intensity) and gas flow conditions based on the operational mode. The controller modifies these parameters in real-time to switch between exposure and cleaning functions, allowing the same apparatus to adapt to different operational requirements without physical reconfiguration
3Reliability
If hydrogen gas is introduced to generate hydrogen radicals for cleaning, then tin compounds are removed as SnH4, but vacuum chamber conditions change
Solution Approach 1:
The vacuum pump operates continuously throughout both exposure and cleaning modes to maintain vacuum conditions. During cleaning, hydrogen gas is introduced temporarily to generate hydrogen tin radicals, but the continuous vacuum pumping ensures that hydrogen partial pressure remains controlled and the overall vacuum environment is preserved, allowing quick return to exposure conditions
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 removes tin compounds from mirrors by increasing hydrogen radical production, enhancing mirror reflectivity and preventing damage, while maintaining operational conditions different from exposure operations.
Implementation Method 1
an irradiator configured to irradiate a pulsed laser onto the target droplet
Implementation Method 2
a condensing mirror inside the vacuum chamber, the condensing mirror being configured to condense a light emitted from the target droplet by irradiation of the pulsed laser onto the target droplet
Implementation Method 3
increase an amount of production of hydrogen radicals in the vacuum chamber
Implementation Method 4
efficiently react and remove tin compounds as SnH4
Data Source
AI summary
An exposure apparatus includes a droplet supplier to supply a target droplet inside a vacuum chamber, an irradiator irradiating a pulsed laser onto the target droplet, a condensing mirror installed inside the vacuum chamber and configured to condense a light emitted from the target droplet by irradiation of the pulsed laser onto the target droplet, a gas supplier to flow a hydrogen gas along a surface of the condensing mirror, a controller to change a supply condition of the target droplet and an irradiation condition of the pulsed laser to conditions different from conditions during an exposure operation to increase an amount of production of hydrogen radicals in the vacuum chamber, and an exhaust pump to exhaust a gas from an inside of the vacuum chamber.