Seed Laser Beam Segmentation in EUV Radiation Source
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Solution Overview
Problem
In extreme ultraviolet (EUV) lithographic apparatuses, the amplified laser radiation can reflect off fuel droplets and return to the seed laser, causing damage due to further amplification in the optical amplifiers.
Innovation Solution
A radiation source design that includes a beam splitter and reflectors to direct the seed laser beam through optical amplifiers in opposite directions, ensuring the amplifiers are depleted of excited electrons, preventing further amplification of the returning beam, and using a polarized beam splitter or directing only a minor portion of the seed laser beam to optical amplifiers to minimize damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the amplified laser radiation is directed at fuel droplets to generate EUV radiation, then EUV radiation is produced effectively, but a portion of the amplified laser radiation reflects off the fuel droplets and returns to the seed laser causing damage
Solution Approach 1:
The laser beam path is segmented into separate directions using beam splitters and reflectors. The seed laser beam is divided and directed through optical amplifiers in opposite directions, so that the amplified beams travel in opposite directions toward fuel droplets. This segmentation ensures that reflected beams from fuel droplets do not return to the seed laser, preventing damage while maintaining effective EUV radiation generation.
Solution Approach 2:
Beam splitters and reflectors are introduced as intermediary components between the seed laser and the fuel droplets. These intermediaries control the direction of laser beams, ensuring that amplified radiation is directed at fuel droplets to generate EUV radiation while preventing reflected radiation from returning to the seed laser.
2Power
If optical amplifiers are used to amplify the seed laser beam, then the laser radiation power is increased for effective EUV generation, but the amplifiers can further amplify the returning reflected beam causing additional damage to the seed laser
Solution Approach 1:
The optical amplification process is segmented into separate directional paths. Beam splitters divide the seed laser beam into multiple paths that pass through optical amplifiers in opposite directions. This ensures that each amplifier only amplifies beams traveling in its designated direction, preventing amplification of reflected beams that return to the seed laser.
Solution Approach 2:
Beam splitters and reflectors serve as intermediary components that control the flow of laser radiation through optical amplifiers. These intermediaries ensure that amplified radiation is directed appropriately at fuel droplets while preventing reflected radiation from re-entering the amplification path and causing additional damage.
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
Prevents damage to the seed laser by eliminating further amplification of the returning beam, while maintaining increased amplification of the seed laser beam, thus ensuring safe operation and efficient EUV radiation generation.
Implementation Method 1
The plasma may be created, for example, by directing a laser beam at a fuel, such as particles (i.e., droplets) of a suitable fuel material (e.g., tin, which is currently thought to be the most promising and thus likely choice of fuel for EUV radiation sources)
Implementation Method 2
A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma
Implementation Method 3
an optical amplifier for receiving the seed laser beam from the beam splitter and performing optical amplification
Implementation Method 4
a first reflector located downstream of the optical amplifier, configured to direct the seed laser beam back through the optical amplifier and on to the beam splitter
Data Source
AI summary
According to a first aspect of the present invention, there is provided a radiation source comprising: a nozzle configured to direct a stream of fuel droplets (70) along a trajectory towards a plasma formation location; a laser configured to direct laser radiation at a fuel droplet at the plasma formation location to generate, in use, a radiation generating plasma; wherein the laser comprises: a seed laser (50) for providing a seed laser beam (52); a beam splitter (54) for receiving the seed laser beam from the seed laser; an optical amplifier (58) for receiving the seed laser beam from the beam splitter and performing optical amplification; a first reflector (60) located downstream of the optical amplifier, configured to direct the seed laser beam back through the optical amplifier and on to the beam splitter; and a second reflector (70) located further downstream of the beam splitter, configured to receive the seed laser beam from the beam splitter and to direct at least a portion of the seed laser beam back toward the beam splitter.