Laser Amplifier Excitation Control for EUV Pulse Stability
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Solution Overview
Problem
Current extreme ultraviolet (EUV) light generating systems for semiconductor photolithography face challenges in maintaining stable pulse energy due to constant excitation intensity in amplifiers, leading to unstable EUV light generation, especially when repetition frequencies change.
Innovation Solution
A laser apparatus with a master oscillator and amplifier system that alternates burst oscillation and suspension periods, controlling excitation intensity based on repetition frequency, adjusting the amplitude and duty ratio of the excitation voltage to maintain consistent gain in amplifiers during both burst and suspension periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant excitation intensity is applied in the amplifier, then the amplifier operates continuously, but the pulse energy becomes unstable when repetition frequency changes
Solution Approach 1:
The patent applies dynamics by making the excitation intensity variable rather than constant. The control unit dynamically adjusts the excitation intensity of the amplifier based on the detected repetition frequency of the pulse laser beam. When the repetition frequency increases, the excitation intensity is increased proportionally, allowing the amplifier to adapt its operation to match the changing pulse frequency and maintain stable pulse energy output.
Solution Approach 2:
The patent implements parameter changes by modifying the excitation intensity parameter in response to repetition frequency changes. The control unit detects the repetition frequency and calculates the appropriate excitation intensity level, then adjusts the amplifier's excitation parameter accordingly. This dynamic parameter adjustment ensures that the amplifier operates optimally across different repetition frequencies, resolving the instability issue.
2Reliability
If excitation intensity is increased to maintain stability at higher repetition frequencies, then pulse energy stability improves, but energy consumption increases
Solution Approach 1:
The patent optimizes energy usage by dynamically adjusting the excitation intensity parameter based on the actual repetition frequency. Instead of maintaining constant high excitation intensity, the control unit calculates the precise excitation level needed for each repetition frequency and applies only that amount. This ensures stable pulse energy output while minimizing unnecessary energy consumption during low-frequency operation.
Solution Approach 2:
The patent implements feedback control where the control unit continuously detects the repetition frequency of the pulse laser beam and uses this information to adjust the amplifier's excitation intensity. This closed-loop feedback mechanism ensures that the excitation intensity is optimized in real-time based on actual operating conditions, maintaining stability while avoiding excessive energy consumption.
3Productivity
If burst oscillation and suspension periods are used, then productivity improves, but maintaining stable gain during suspension periods becomes difficult
Solution Approach 1:
The patent applies dynamics by continuously monitoring the repetition frequency during both burst oscillation and suspension periods and dynamically adjusting the excitation intensity accordingly. Even during suspension periods when no pulses are output, the control unit maintains appropriate excitation levels based on the detected repetition frequency, ensuring that the amplifier gain remains stable and ready for the next burst oscillation.
Solution Approach 2:
The patent implements feedback control that operates continuously through both burst oscillation and suspension periods. The control unit detects the repetition frequency at all times and adjusts the amplifier's excitation intensity to maintain stable gain. This continuous feedback mechanism ensures that when burst oscillation resumes after a suspension period, the amplifier is already at the correct excitation level, maintaining productivity while ensuring stability.
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 the pulse energy of the amplified laser beam, reducing unintended changes in EUV light energy generated, even when repetition frequencies vary, thereby enhancing the stability and consistency of the EUV light generation process.
Implementation Method 1
an amplifier provided in an optical path of the pulse laser beam outputted from the master oscillator
Data Source
AI summary
The laser apparatus includes a master oscillator, an amplifier, a power source, and a controller to control the power source. The controller controls the power source such that an excitation intensity of the amplifier in a burst oscillation period performing the burst oscillation is a first excitation intensity, controls the power source such that, if the predetermined repetition frequency is a first repetition frequency, an excitation intensity of the amplifier in a suspension period suspending the burst oscillation is a second excitation intensity equal to or lower than the first excitation intensity, and controls the power source such that, if the predetermined repetition frequency is a second repetition frequency higher than the first repetition frequency, the excitation intensity of the amplifier in the suspension period is a third excitation intensity lower than the second excitation intensity.