Laser Amplification Control for Narrow Spectral Line Width
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Solution Overview
Problem
In semiconductor exposure apparatuses, the use of KrF and ArF excimer lasers results in significant chromatic aberration due to their large spectral line widths, which can decrease resolution, and existing methods to narrow the spectral line width are inadequate.
Innovation Solution
A control method for a laser system that determines the condition under which the amplification characteristic of the amplification stage laser changes, acquires the relationship between pulse energy of the first laser light and parameters of the second laser light, and sets the target pulse energy based on this relationship to optimize the laser output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module including a line narrowing element is provided in a laser resonator to narrow a spectral line width, then chromatic aberration is reduced, but device complexity increases
Solution Approach 1:
The patent changes the operational parameters of the oscillation stage laser (pulse energy, repetition period) to control the amplification characteristic of the amplification stage laser. By setting specific target pulse energy values and adjusting the repetition period dynamically, the system achieves optimal laser beam quality and narrows the spectral line width without adding physical line narrowing modules, thus resolving the contradiction between manufacturing precision and device complexity
Solution Approach 2:
The patent replaces the mechanical/optical line narrowing module (etalon, grating) with a control system that uses electrical parameters (pulse energy, repetition period) to achieve the same effect of narrowing spectral line width. This substitution eliminates the need for additional optical components while maintaining or improving resolution
2Manufacturing precision
If the spectral line width of laser light is narrowed using a line narrowing module, then chromatic aberration is reduced, but the lifetime of laser chambers decreases
Solution Approach 1:
The patent uses parameter changes in the oscillation stage laser (pulse energy, repetition period) to control the amplification process in the amplification stage laser. By optimizing these parameters, the system achieves narrow spectral line width and high resolution without the need for line narrowing modules that would otherwise reduce laser chamber lifetime
Solution Approach 2:
The patent extracts and removes the line narrowing module from the laser resonator system. By taking out the problematic component (line narrowing module including etalon or grating), the system eliminates the source of reduced laser chamber lifetime while maintaining resolution through alternative parameter control methods
3Productivity
If target pulse energy is not appropriately set, then laser output characteristics are not optimized, but increasing pulse energy may reduce laser chamber lifetime
Solution Approach 1:
The patent implements a feedback control mechanism where the processor monitors the actual pulse energy output and adjusts the repetition period accordingly. The system compares actual output with target values and dynamically modifies operating parameters to maintain optimal pulse energy while preventing excessive energy levels that would reduce laser chamber lifetime
Solution Approach 2:
The patent introduces dynamic adjustment of the repetition period based on actual laser output conditions. Instead of using a fixed repetition period, the system continuously adapts the timing between pulses to maintain optimal energy levels, allowing the system to respond to changing conditions and prevent damage to laser chambers while maintaining high productivity
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 allows for improved resolution by appropriately setting the target pulse energy, reducing chromatic aberration and extending the lifetime of the laser chambers, while ensuring the desired characteristics of the second laser light are maintained.
Implementation Method 1
an amplification stage laser configured to amplify the first laser light and output second laser light
Data Source
AI summary
A laser system includes an oscillation stage laser configured to output first laser light, and an amplification stage laser configured to amplify the first laser light and output second laser light. A control method of the laser system includes determining a condition under which an amplification characteristic of the amplification stage laser changes, acquiring relationship between pulse energy of the first laser light and a parameter of the second laser light when the condition is determined to be satisfied, and setting target pulse energy of the first laser light based on the relationship.