EUV Light Generation Optical Path Alignment Control
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Solution Overview
Problem
In extreme ultraviolet light generation systems, the optical path axis shift during burst-off durations leads to reduced EUV light energy at the start of burst-on durations due to thermal changes in optical elements, affecting exposure performance.
Innovation Solution
Incorporating an optical sensor to detect reflected light from guide lasers, allowing for precise control of the optical path axis during burst-off durations to maintain alignment and stabilize EUV light energy by adjusting the focusing position based on reflected light measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If focusing position control is performed frequently to maintain optical path alignment, then optical path stability is improved, but system complexity and control frequency increase
Solution Approach 1:
The patent employs feedback control by detecting the position of the guide laser beam spot on the target surface and using this information to adjust the focusing position. The control unit continuously monitors the beam spot position and modifies the focusing position accordingly, creating a closed-loop feedback system that maintains optical path stability without requiring overly complex control mechanisms.
Solution Approach 2:
The guide laser beam itself serves as the reference for positioning the drive laser beam. By using the guide laser beam spot position as the feedback signal, the system performs self-alignment without requiring external reference systems or additional complex alignment mechanisms, thereby maintaining simplicity while achieving stability.
2Reliability
If focusing position is adjusted frequently to compensate for thermal changes, then EUV light energy consistency is improved, but control frequency and processing time increase
Solution Approach 1:
The system performs focusing position adjustments during the burst-off duration, which is the idle period between EUV light generation bursts. This preliminary action ensures that the optical path is realigned before the next EUV light generation begins, maintaining energy consistency without interrupting the productive burst-on periods or adding processing time to the critical path.
Solution Approach 2:
The focusing position control is implemented periodically during burst-off durations rather than continuously during burst-on durations. This periodic action maintains EUV light energy consistency by compensating for thermal changes that occur during idle periods, while minimizing control processing time by avoiding adjustments during the critical EUV light generation periods.
3Measurement precision
If guide laser beam is used for positioning, then alignment precision is improved, but system complexity increases due to additional optical components
Solution Approach 1:
The patent merges the functions of the guide laser beam and drive laser beam through a beam combiner, allowing both beams to share the same optical path. This combining approach enables the guide laser beam to provide precise positioning information while the drive laser beam generates EUV light, without requiring completely separate optical systems, thereby reducing overall system complexity.
Solution Approach 2:
The guide laser beam serves multiple functions: it provides a reference for positioning, enables detection of beam spot position on the target surface, and facilitates alignment of the drive laser beam. This multi-functionality allows a single optical component (the guide laser) to perform multiple roles, reducing the need for additional specialized components and simplifying the overall optical system.
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 consistent and desired EUV light energy levels at the start of burst-on durations, improving exposure performance and reducing the frequency of focusing position controls.
Implementation Method 1
The optical sensor detects reflected light of the guide laser beam from the target
Implementation Method 2
The laser beam focusing optical system focuses the drive laser beam and the guide laser beam output from the beam combiner to the predetermined region
Implementation Method 3
a laser produced plasma (LPP) apparatus using plasma generated by irradiating a target substance with a pulse laser beam
Data Source
AI summary
An extreme ultraviolet light generation system includes: a target supply unit configured to output a target toward a predetermined region; a drive laser configured to output a drive laser beam in a first duration; a guide laser configured to output a guide laser beam; a beam combiner configured to substantially align the optical path axes of the drive and guide laser beams and output the laser beams; a laser beam focusing optical system configured to focus the laser beams output from the beam combiner to the predetermined region; an actuator configured to change the focusing positions of the laser beams through the laser beam focusing optical system; an optical sensor configured to detect reflected light of the guide laser beam from the target; and a control unit configured to control the actuator so that the light amount of the reflected light thus detected increases in a second duration.