EUV Target Reflection Aberration Control for Stable Energy Output
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Solution Overview
Problem
Existing EUV lithography systems face challenges in maximizing EUV energy output due to issues with the shape of the excitation laser, angle of incidence, and laser beam profile, which are not adequately detected and compensated, leading to inefficiencies in the interaction between the excitation laser and target droplets.
Innovation Solution
The system controls the relative position and angle of the excitation laser and target droplets by analyzing the aberrations in the laser beam using Zernike polynomials, adjusting the position of mirrors, and optimizing the interaction through a feedback mechanism to enhance EUV energy generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the excitation laser parameters (shape, angle of incidence, beam profile) are not controlled, then the system operation is simpler, but the EUV energy output and conversion efficiency deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the actual laser parameters (beam shape, angle of incidence, beam profile) are measured and compared against target values. Control signals are then generated to adjust the laser system parameters, creating a closed-loop control system that automatically maintains optimal EUV energy output without requiring complex manual intervention
Solution Approach 2:
The patent replaces complex mechanical adjustment mechanisms with electronic control and optical feedback systems. Instead of physically adjusting mirrors and lenses through mechanical means, the system uses electronic control signals to adjust laser parameters based on optical feedback from wavefront sensors and beam diagnostics
2Loss of energy
If the interaction between excitation laser and target droplets is optimized, then the EUV conversion efficiency improves, but the difficulty of detecting and measuring laser parameters increases
Solution Approach 1:
The patent introduces intermediary diagnostic devices such as wavefront sensors and beam profile monitors that indirectly measure laser parameters. These intermediaries convert difficult-to-measure laser characteristics into detectable signals that can be used for feedback control, enabling efficient measurement without direct interference with the laser-target interaction
Solution Approach 2:
The patent changes the measurement parameters from direct laser field measurements to indirect measurements using optical probes and sensors. By measuring parameters such as wavefront distortion and beam intensity distribution at strategic locations, the system infers critical laser parameters without requiring direct measurement of the excitation laser itself
3Stability of the object's composition
If the laser beam parameters fluctuate, then the system operation is less complex, but the stability of EUV energy output deteriorates
Solution Approach 1:
The patent employs continuous feedback monitoring of laser beam parameters including wavefront distortion, beam profile, and angle of incidence. When fluctuations are detected, the system automatically generates correction signals to stabilize these parameters, maintaining consistent EUV energy output through real-time adjustments without requiring overly complex control architecture
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 stabilizes EUV energy output by minimizing fluctuations and improving the conversion efficiency of EUV radiation, ensuring consistent and optimal interaction between the excitation laser and target droplets.
Implementation Method 1
a high-power laser beam is focused on small droplet targets of metal, such as tin, to form a highly ionized plasma that emits EUV radiation with a peak maximum emission at 13.5 nm
Implementation Method 2
detecting laser radiation reflected by the target droplet
Data Source
AI summary
A method of controlling an extreme ultraviolet (EUV) lithography system is disclosed. The method includes irradiating a target droplet with EUV radiation, detecting EUV radiation reflected by the target droplet, determining aberration of the detected EUV radiation, determining a Zernike polynomial corresponding to the aberration, and performing a corrective action to reduce a shift in Zernike coefficients of the Zernike polynomial.