Droplet Target Control for EUV Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current EUV sources face spatial and temporal instabilities in droplet targets during high-repetition-rate laser interactions, leading to variations in EUV emission due to lateral and axial instabilities, which affect the precision and stability of the droplet position and synchronization with the laser pulse.
Innovation Solution
A method and apparatus using a limited number of photodiode sensors and laser beams to actively track and control the droplet target position and velocity, employing a feedback system to realign the droplet generator and adjust the laser pulse timing to maintain precise alignment and synchronization, ensuring high spatial resolution and response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a closed loop control system is used to correct droplet position drifts, then droplet target stability is improved, but device complexity increases
Solution Approach 1:
The patent implements a closed-loop feedback control system where photodiode sensors continuously monitor droplet position, and the controller adjusts droplet generation parameters in real-time based on measured deviations from the desired position, thereby maintaining stability without requiring overly complex mechanical correction mechanisms
Solution Approach 2:
The patent replaces complex mechanical position adjustment systems with an electronic feedback control approach that uses photodiode sensing and electronic signal processing to correct droplet position drifts, reducing mechanical complexity while maintaining control effectiveness
2Measurement precision
If high precision sensors are used to track droplet position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential measurement function by using simple photodiode sensors that detect droplet position through optical absorption or scattering, eliminating the need for complex sensor assemblies while achieving sufficient measurement precision for feedback control
Solution Approach 2:
The patent employs inexpensive photodiode sensors rather than expensive high-precision position sensors, accepting that these simpler sensors require careful positioning and calibration but providing cost-effective measurement capability for the feedback system
3Stability of the object's composition
If the droplet generator is realigned frequently to maintain position, then droplet target stability is improved, but loss of time increases
Solution Approach 1:
The patent performs preliminary alignment of the droplet generator during system setup and uses the feedback control system to make only minor real-time adjustments, avoiding frequent major realignments and reducing the time lost to position correction while maintaining droplet stability
Solution Approach 2:
The patent implements dynamic feedback control that continuously monitors droplet position and makes real-time adjustments to the droplet generation parameters, allowing the system to adapt to position drifts without requiring frequent manual realignments and minimizing operational interruptions
4Measurement precision
If laser pulse timing is adjusted frequently to maintain synchronization, then synchronization precision is improved, but loss of time increases
Solution Approach 1:
The patent uses feedback from photodiode sensors that detect droplet position and timing to automatically adjust laser pulse synchronization, eliminating the need for manual timing adjustments and reducing time loss while maintaining precise synchronization between laser pulses and droplet passage
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
The system achieves high precision in maintaining droplet target position and synchronization, reducing lateral and axial instabilities, and enhancing the stability and consistency of EUV emission, with a spatial resolution of micrometers and response time of milliseconds.
Implementation Method 1
the actual position of individual droplets of the droplet target is measured; the velocity of individual droplets of the droplet target is measured
Implementation Method 2
Laser Produced Plasma (LPP) when tin is used as the fuel. For the LPP, a laser beam (generally a ND:YAG or a CO2 laser) having a power on the order of kilowatts with pulse lengths on the order of nanoseconds is focused onto solid or liquid tin targets
Implementation Method 3
A laser power density of about 1010-1011 W/cm2 will be delivered to the target, thus generating first the vaporization of the solid material and then the plasma
Implementation Method 4
said actual position and said velocity of individual droplets of the droplet target is measured optically
Data Source
AI summary
A method for controlling an interaction between droplet targets and a high power and high-repetition-rate laser beam at a laser focus position of the laser beam including providing a droplet generator for generating a train of droplets as a droplet target with a predetermined droplet frequency and velocity in a predetermined direction; providing a high power, high-repetition-rate laser for emitting a pulsed laser beam, which is focused in the laser focus position; aligning the droplet generator such that the train of droplets runs through the laser focus position; generating a train of droplets as a droplet target; and emitting a pulsed laser beam in synchronization with the train of droplets, such that the droplet target interacts with the pulsed laser beam at the laser focus position.