Laser Bandwidth Stabilization via Differential Firing Time
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Solution Overview
Problem
Existing active bandwidth control systems for DUV laser light sources in photolithography take too long to recover from disturbances and can result in significant bandwidth deviations, especially at low duty cycles, leading to errors and instability in maintaining target bandwidth settings.
Innovation Solution
A tunable advanced bandwidth stabilization system using a multi-stage control approach with variable magnification line narrowing modules, differential firing time, and precise actuator control, including rotational prisms and PZT stacks, to maintain bandwidth within ±50 fm and center wavelength stability, enabling rapid correction and minimizing impact on other laser parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing active bandwidth control systems are used, then bandwidth control is implemented, but recovery time from disturbances is too long and bandwidth deviations occur
Solution Approach 1:
The control system is divided into two independent stages: a master oscillator stage that generates stable broadband radiation and an amplifier stage that provides gain. This segmentation allows the master oscillator to maintain precise frequency control while the amplifier provides power, enabling faster response to disturbances without compromising bandwidth stability.
Solution Approach 2:
The system implements feedback control by monitoring the laser output and adjusting the differential firing time between master oscillator and amplifier discharge. This feedback mechanism detects bandwidth deviations and automatically corrects them by modifying the timing relationship, significantly reducing recovery time from disturbances and maintaining bandwidth within ±50 fm of the target.
2Measurement precision
If existing active bandwidth control systems are used, then bandwidth control is implemented, but significant bandwidth deviations occur at low duty cycles
Solution Approach 1:
The system dynamically adjusts the differential firing time between master oscillator and amplifier based on the duty cycle and disturbance conditions. By making the timing relationship variable rather than fixed, the system maintains precise bandwidth control across the full duty cycle range from continuous wave operation down to single-shot mode, adapting its control strategy to match the operating conditions.
3Reliability
If multi-stage control actuators are used, then bandwidth control authority is improved, but complexity of the system increases
Solution Approach 1:
The patent extracts and isolates the bandwidth control function to a specific degree of freedom: the differential firing time between master oscillator and amplifier. By separating this control function from other laser parameters and dedicating it to a single adjustable parameter, the system achieves comprehensive bandwidth control authority without proportionally increasing overall system complexity. Other parameters remain relatively simple and independent.
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
The system achieves rapid recovery and precise control of bandwidth, maintaining stability within ±50 fm and minimizing wavelength errors, ensuring efficient and accurate photolithography processes.
Implementation Method 1
a line narrowing module having a variable magnification and including a diffraction grating
Implementation Method 2
at least one actuator which is a PZT stack
Data Source
AI summary
According to aspects of an embodiment of the disclosed subject matter, method and apparatus are disclose that may comprise adjusting a differential timing between gas discharges in the seed laser and amplifier laser for bandwidth control, based on the error signal, or for control of another laser operating parameter other than bandwidth, without utilizing any beam magnification control, or adjusting a differential timing between gas discharges in the seed laser and amplifier laser for bandwidth control, based on the error signal, or for control of another laser operating parameter other than bandwidth, while utilizing beam magnification control for other than bandwidth control, and adjusting a differential timing between gas discharges in the seed laser and amplifier laser for bandwidth control, based on the error signal, or for control of another laser operating parameter other than bandwidth, while utilizing beam magnification control for bandwidth control based on the error signal.