LPP EUV Droplet Steering and Timing Control
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Solution Overview
Problem
Current EUV light sources face challenges in accurately controlling the trajectory and timing of droplets to ensure effective irradiation in LPP EUV systems, particularly in MOPA and MOPA PP systems, where the source laser needs to be fired synchronously with the droplet's arrival at the irradiation site, requiring precise steering and timing mechanisms.
Innovation Solution
A system utilizing two laser curtains, one for droplet trajectory correction and the other for timing the source laser pulse, with sensors detecting flashes to determine the droplet's position and speed, generating signals to adjust the droplet generator's direction and timing the source laser to irradiate the droplet at the correct moment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser curtain is used for droplet detection, then the system structure is simpler, but the precision of droplet trajectory control and timing is insufficient
Solution Approach 1:
The patent divides the droplet detection and control function into two separate laser curtains: a first laser curtain for trajectory detection and a second laser curtain for timing detection. This segmentation allows each curtain to specialize in one measurement task, improving overall precision while maintaining manageable system complexity through modular functionality.
Solution Approach 2:
The patent adds a temporal dimension to the detection system by using a second laser curtain positioned at a different location to measure droplet arrival time, while the first laser curtain measures spatial trajectory. This multi-dimensional approach simultaneously captures both position and timing information without requiring a single complex detection system.
2Measurement precision
If two laser curtains are used for droplet detection, then the precision of droplet trajectory control and timing is improved, but the system complexity increases
Solution Approach 1:
Both laser curtains serve multiple purposes: they detect droplet position, determine trajectory, and provide timing information. The first laser curtain's trajectory data can be used for both spatial control and temporal synchronization, while the second laser curtain provides both positioning and timing reference, reducing the need for additional specialized components.
Solution Approach 2:
The patent introduces a control system that acts as an intermediary, processing signals from both laser curtains and coordinating the droplet generator and laser firing. This centralized control mechanism manages the increased system complexity by integrating information from multiple sensors and coordinating multiple actuators through a unified control architecture.
3Illumination intensity
If the source laser is fired continuously, then the EUV light output is maintained, but the energy efficiency decreases
Solution Approach 1:
The source laser operates in periodic pulses rather than continuously, firing only when a droplet is detected by the laser curtains and determined to be on the correct trajectory. This periodic operation synchronized with droplet arrival maintains EUV light output when needed while eliminating energy waste during periods when no droplet is present or trajectory is incorrect.
Solution Approach 2:
The system uses feedback from the laser curtains' droplet detection to control the source laser firing. When the curtains detect a droplet on the correct trajectory, the control system triggers the source laser to fire; when no droplet is detected or the trajectory is incorrect, the laser remains off. This feedback-based control optimizes energy efficiency by matching laser operation to actual processing needs.
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 ensures precise control over droplet trajectory and timing, enhancing the efficiency and reliability of EUV light production by ensuring the source laser pulses intersect the droplets at the optimal moment, improving EUV light output and system performance.
Implementation Method 1
a first sensor configured to detect a flash when the droplet passes through the first laser curtain
Implementation Method 2
the source laser fires a pulse at the determined time, such that the pulse irradiates the droplet at the irradiation site
Implementation Method 3
When the laser pulse hits the droplets at the irradiation site, the droplets are vaporized
Implementation Method 4
the reflective collector causes the resulting EUV light output to be maximized at another focal point of the collector
Data Source
AI summary
A method and apparatus for improved control of the trajectory and timing of droplets of target material in a laser produced plasma (LPP) extreme ultraviolet (EUV) light system is disclosed. A droplet illumination module generates a laser curtain, and sensors detect the droplets as they pass through the curtain. One sensor in combination with a controller detects the position of the droplets relative to a desired trajectory to the irradiation site so that a signal can be sent to an actuator of a droplet generator to adjust orientation of the droplet generator and direct subsequent droplets to the irradiation site, as in the prior art. A second sensor, or droplet detection module, also detects each droplet as it passes through the curtain, and in combination with a controller determines when the source laser should generate a pulse so that the pulse will arrive at the irradiation site at the same time as the droplet, and sends a signal to the source laser to fire at the correct time.