LPP EUV Laser Timing Control via Droplet Feedback
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Solution Overview
Problem
In laser produced plasma (LPP) extreme ultraviolet (EUV) light sources, accurately timing the source laser to intersect with droplets at the irradiation site is challenging, particularly in MOPA and MOPA PP systems, leading to suboptimal EUV light generation due to droplet slowing and positioning issues.
Innovation Solution
A method and system that utilize an EUV energy detector to measure the energy generated from impacting droplets and a delay module to calculate and adjust the timing of subsequent laser pulses, ensuring they irradiate droplets at the irradiation site, thereby compensating for droplet slowing and improving EUV light production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the source laser is fired at fixed intervals in MOPA systems, then the system operation is simplified, but the timing precision between laser pulses and droplet arrival at the irradiation site deteriorates
Solution Approach 1:
The system uses EUV energy detection from previous droplet irradiations to provide feedback about droplet arrival timing. The delay module adjusts subsequent laser pulse timing based on this feedback, creating a closed-loop control system that maintains precise synchronization between laser pulses and droplet arrival without requiring complex real-time measurement systems.
Solution Approach 2:
The system performs preliminary measurement of EUV energy from each droplet irradiation event and uses this information to pre-calculate the optimal delay for the next laser pulse. This preliminary action allows the system to adjust timing proactively rather than reactively, ensuring precise synchronization is maintained for each subsequent droplet-laser interaction.
2Ease of operation
If the source laser is continuously on in NoMO systems, then droplet timing control is simplified, but energy consumption increases and laser damage risk increases
Solution Approach 1:
The MOPA system uses periodic laser pulsing instead of continuous operation, synchronizing laser pulses with droplet arrival at the irradiation site. This periodic action dramatically reduces average power consumption and thermal load on the laser while maintaining effective irradiation, as the laser is only active when a droplet is present to be irradiated.
Solution Approach 2:
The system uses the droplets themselves as timing references - each droplet's arrival at the irradiation site naturally triggers the next laser pulse through the EUV energy detection and delay mechanism. This self-service approach eliminates the need for external continuous control signals while maintaining precise synchronization.
3Device complexity
If the laser pulses are fired without timing adjustment, then the system complexity is reduced, but the EUV energy generation efficiency deteriorates due to droplet slowing
Solution Approach 1:
The system measures EUV energy output from each droplet irradiation as feedback about the quality of the droplet-laser interaction. This feedback is used to calculate and adjust the timing delay for subsequent pulses, creating a self-optimizing system that maintains high EUV generation efficiency despite variations in droplet velocity and arrival timing.
Solution Approach 2:
The system replaces complex real-time mechanical measurement and adjustment mechanisms with a simpler optical-electrical feedback system. By using EUV energy detection (optical) and electronic delay adjustment, the system achieves precise timing control without requiring mechanical sensors or actuators at the irradiation site.
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 approach enhances the timing precision of laser pulses, leading to increased EUV energy generation by ensuring optimal droplet irradiation and plasma formation, thereby improving the efficiency and reliability of EUV light production in LPP systems.
Implementation Method 1
When the laser pulse hits the droplets at the irradiation site, the droplets are vaporized and the reflective collector causes the resulting EUV light output to be maximized
Implementation Method 2
the reflective collector causes the resulting EUV light output to be maximized at another focal point of the collector
Data Source
AI summary
Methods and systems for improved timing of a source laser in a laser produced plasma (LPP) extreme ultraviolet (EUV) generation system are disclosed. Due to forces within the plasma chamber, a velocity of a droplet can slow as it approaches the irradiation site. Because the droplet is slowed, a source laser fires prematurely relative to the slowed droplet, resulting in only a leading portion of the droplet being irradiated. The resulting amount of EUV energy generated from the droplet is proportional to the slowed velocity of the droplet. To compensate, the firing of the source laser is delayed for a next droplet based on the generated EUV energy. Because the firing of the source laser is delayed for the next droplet, the next droplet is more likely to be in position to be more completely irradiated, resulting in more EUV energy being generated from the next droplet.