EUV Light Source Wavefront Correction via Guide Laser Feedback
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Solution Overview
Problem
High-power laser beams used in extreme ultraviolet light source devices experience optical performance variations due to heat and mechanical vibrations, leading to unstable EUV light output, as optical elements absorb the laser and change temperature, affecting the wavefront and focal position, thereby reducing EUV light production.
Innovation Solution
An extreme ultraviolet light source device is designed with a guide laser beam system that corrects optical performance by introducing a guide laser beam along the driver pulsed laser beam path, using a guide laser beam detection system to stabilize the optical performance, both during and outside the driver pulsed laser beam output, with the guide laser beam having a similar beam diameter and wavelength to the driver beam, and being used as a continuous or pseudo-continuous light to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high output power laser beam is used to generate sufficient EUV light, then EUV light output power is improved, but optical elements absorb the laser and become high temperature causing wave front variation
Solution Approach 1:
A guide laser beam is introduced as an intermediary to monitor the optical path. The guide laser beam travels through the same optical elements as the driver pulsed laser beam, allowing detection of wave front variations caused by temperature changes in optical elements without using the high-power driver beam for monitoring purposes
2Power
If high output power laser beam is used to generate sufficient EUV light, then EUV light output power is improved, but focal position varies due to wave front variation
Solution Approach 1:
The system implements feedback control by detecting the wave front of the guide laser beam with a wave front sensor and adjusting the deformable mirror accordingly. This feedback mechanism compensates for focal position variations caused by temperature-induced wave front changes in optical elements, maintaining accurate focal positioning despite high power operation
Solution Approach 2:
A deformable mirror with dynamically adjustable surface shape is used to compensate for wave front variations. The mirror can change its focal position and wave front characteristics in real-time based on feedback from the guide laser beam detection, allowing the system to adapt to temperature changes and maintain manufacturing precision
3Reliability
If guide laser beam system is added to correct optical performance, then optical performance stability is improved, but device complexity increases
Solution Approach 1:
The guide laser beam system serves multiple functions: it monitors the optical path, detects wave front variations, and enables feedback control for correction. By using a single guide laser beam for multiple monitoring and control purposes, the system achieves high reliability without proportionally increasing device complexity
Solution Approach 2:
The guide laser beam creates a copy of the driver pulsed laser beam's optical path. This copy allows monitoring and correction without interfering with the actual high-power EUV generation process, simplifying the control architecture while maintaining reliability
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 configuration ensures immediate correction of optical performance variations, stabilizing the driver pulsed laser beam and improving the reliability of the EUV light source by maintaining stable optical performance, even under heat and vibration loads, without complicating the device configuration.
Implementation Method 1
an LPP (Laser Produced Plasma: plasma produced by a laser) type light source, which generates a plasma by irradiating a target material with a laser beam, and employs an EUV light that is emitted from this plasma
Implementation Method 2
a guide laser device that outputs a guide laser beam; a guide laser beam detection part that detects an optical performance of the guide laser beam
Data Source
AI summary
A guide laser beam that has an optical axis and a beam diameter substantially equivalent to those of a driver pulsed laser beam is introduced into an amplification system that amplifies a laser beam that is output from a driver laser oscillator. The guide laser beam is output from a laser device as a continuous light, and is introduced into a light path of the driver pulsed laser beam via a guide laser beam introduction mirror. A sensor detects an angle (a direction) of a laser beam and a variation of a curvature of a wave front. A wave front correction controller outputs a signal to a wave front correction part based on a measured result of a sensor. The wave front correction part corrects a wave front of a laser beam to be a predetermined wave front according to an instruction from the wave front correction controller.