Excimer Laser Resonator Control for Stable Narrow Linewidth Output
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Solution Overview
Problem
Existing gas laser apparatuses, such as KrF and ArF excimer lasers, suffer from chromatic aberration due to wide spectrum line widths, which degrade resolving power in semiconductor exposure processes, necessitating a solution to narrow the spectrum line width to mitigate chromatic aberration.
Innovation Solution
A gas laser apparatus with a laser oscillator, amplifier, beam splitter, optical sensor, and processor is configured to control voltage based on optical sensor feedback, incorporating a grating and output coupling mirrors to stabilize laser output and maintain voltage above a threshold, even in degeneracy control modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a line narrowing module (LNM) including a line narrowing element is provided in a laser resonator to narrow the spectrum line width, then chromatic aberration is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the line narrowing function from a separate module and integrates it into the resonator structure itself through carefully designed mirror surfaces. The resonator mirrors are configured to provide both feedback and line narrowing functions simultaneously, eliminating the need for a separate LNM and reducing overall device complexity while maintaining chromatic aberration reduction.
Solution Approach 2:
The patent merges the line narrowing element with the resonator mirrors, combining multiple functions (light feedback and spectrum narrowing) into a single integrated component. This consolidation reduces the number of separate elements in the system while achieving the desired optical performance.
2Reliability
If voltage is reduced to prevent degradation of the laser oscillator, then operation stability is improved, but light output amount decreases
Solution Approach 1:
The patent implements a feedback control system using an optical sensor to detect light output and a processor to adjust voltage dynamically. When light output falls below a threshold, the system automatically increases voltage to restore output levels, preventing the need to operate at consistently reduced voltages and thereby maintaining both stability and sufficient power output.
Solution Approach 2:
The patent transitions from static voltage operation to dynamic voltage control, where the voltage applied to the laser oscillator is continuously adjusted based on real-time light output measurements. This dynamic adjustment allows the system to maintain optimal performance across varying operating conditions without compromising either stability or power output.
3Power
If voltage is increased to maintain light output amount, then power is improved, but degradation of the laser oscillator accelerates
Solution Approach 1:
The feedback control system monitors light output and applies voltage only when necessary to maintain output above a threshold. This on-demand voltage adjustment prevents continuous high-voltage operation that would accelerate degradation, while still ensuring sufficient power output when needed, thereby extending laser oscillator life.
Solution Approach 2:
The patent dynamically changes the voltage parameter based on light output conditions, transitioning between low-voltage (preservative) and high-voltage (powerful) states as needed. This adaptive parameter adjustment optimizes the balance between power output and component longevity.
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
Stabilizes laser output and maintains performance by preventing unstable light amounts, ensuring reliable operation and meeting exposure apparatus requirements, thereby enhancing the gas laser apparatus's reliability and stability.
Implementation Method 1
a pair of discharge electrodes and configured to generate light from laser gas upon application of voltage
Implementation Method 2
The laser-side resonator may include a grating that reflects the light generated from the laser gas
Implementation Method 3
a beam splitter configured to reflect a part of the light from the laser-side resonator
Implementation Method 4
an optical sensor configured to detect the light reflected by the beam splitter
Data Source
AI summary
A gas laser apparatus includes a laser oscillator including a pair of discharge electrodes disposed to face each other and configured to generate light from laser gas upon application of voltage, and a laser-side resonator in which the light resonates; an amplifier including an amplification unit and an amplification-side resonator; a beam splitter configured to reflect a part of the light from the laser-side resonator; an optical sensor configured to detect the light reflected by the beam splitter; and a processor configured to control the voltage based on an output from the optical sensor. The amplification-side resonator includes a rear mirror and an output coupling mirror. The laser-side resonator includes a grating and an output coupling mirror. The processor maintains the voltage at a constant value equal to or larger than a threshold of the voltage when the voltage is to be smaller than the threshold.