EUV Laser Pulse Timing Feedback Control
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Solution Overview
Problem
In extreme ultraviolet (EUV) lithography systems, the synchronization of target droplets with the excitation laser pulses is crucial for efficient plasma generation, but mechanical and electrical drifts cause misalignment, leading to reduced EUV radiation intensity and dose errors during lithography exposure.
Innovation Solution
A feedback control system adjusts the time delay between pre-pulse and main pulse of the excitation laser based on EUV energy measurements, using an energy detector and actuator to maintain optimal droplet illumination, ensuring precise synchronization and alignment of laser pulses with target droplets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser pulses are synchronized with target droplet generation and movement, then EUV radiation intensity is improved, but mechanical and electrical drifts cause misalignment leading to reduced intensity
Solution Approach 1:
The patent employs a feedback control system that continuously monitors the position of target droplets and adjusts the timing of laser pulses accordingly. Sensors detect droplet position and this information is fed back to the laser control system, which dynamically adjusts the pulse timing to maintain optimal synchronization despite mechanical and electrical drifts, thereby preserving EUV radiation intensity
Solution Approach 2:
The system transitions from static, pre-programmed laser timing to dynamic, real-time adjustment of pulse timing. The laser synchronization system continuously adapts its timing parameters based on actual droplet position measurements, making the system flexible and responsive to changing conditions, thus maintaining optimal synchronization under varying operational conditions
2Measurement precision
If precise synchronization is maintained to improve EUV energy production, then dose accuracy is improved, but drift causes dose errors
Solution Approach 1:
The feedback control system monitors actual droplet positions and laser pulse timing, comparing them against desired parameters. When deviations are detected, the system automatically adjusts timing to correct the misalignment, ensuring that the EUV energy delivered to the photomask maintains accurate dosimetry despite drift conditions
Solution Approach 2:
The system performs preliminary measurements of droplet position and velocity before the main laser pulse arrives. This advance information is used to predict and compensate for potential misalignment, allowing the control system to pre-adjust timing parameters to ensure accurate dose delivery
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 stability and efficiency of the laser-produced plasma (LPP) EUV source by maintaining optimal EUV energy production, reducing dose errors and improving the accuracy of EUV lithography processes.
Implementation Method 1
A feedback control system adjusts the time delay between pre-pulse and main pulse of the excitation laser based on EUV energy measurements
Implementation Method 2
a feedback control system adjusts the time delay between pre-pulse and main pulse of the excitation laser based on EUV energy measurements
Data Source
AI summary
An apparatus for generating extreme ultraviolet (EUV) radiation comprises a droplet generator, an excitation laser source, an energy detector, and a feedback controller. The droplet generator is configured to generate target droplets. The excitation laser is configured to generate a pre-pulse and a main pulse to convert the target droplets to plasma by heating. The energy detector is configured to measure a variation in EUV energy generated when the target droplets are converted to plasma. The feedback controller is configured to adjust a time delay between a subsequent pre-pulse and main pulse generated by the excitation laser based on the variation in EUV energy generated by a given main pulse.