Faraday Optical Pulse Stretcher for Flexible Pulse Width Control
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Solution Overview
Problem
Current semiconductor exposure apparatuses face challenges in achieving optimal resolution due to chromatic aberration caused by wide spectral linewidths of KrF and ArF excimer laser beams, leading to decreased resolution and the need for complex and labor-intensive adjustments in optical pulse stretchers to change pulse widths or waveforms.
Innovation Solution
The implementation of an optical pulse stretcher comprising a polarizer, a delay optical system with multiple mirrors, and a Faraday rotator, which includes a magnet and Faraday material, allows for the rotation of the polarization direction of the pulse laser beam, enabling flexible control of pulse width and waveform without requiring changes to the optical system components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module (LNM) including a line narrowing element (etalon or grating) is provided in the laser resonator to narrow the spectral linewidth, then chromatic aberration is reduced and resolution is improved, but device complexity increases
Solution Approach 1:
The patent extracts the line narrowing function from the laser resonator system by placing a line narrowing module in the optical pulse stretcher path. This separates the pulse stretching function from the line narrowing function, allowing the laser resonator to remain simple while still achieving narrow spectral linewidth through the extracted line narrowing element in the stretcher configuration.
Solution Approach 2:
The patent introduces an intermediary line narrowing module within the optical pulse stretcher that acts as a mediator between the laser beam and the final output. This intermediary component enables spectral linewidth control without requiring direct modification of the laser resonator structure, thus reducing overall device complexity while maintaining resolution.
2Manufacturing precision
If optical components are replaced or adjusted to change pulse width or waveform in conventional optical pulse stretchers, then pulse parameters can be optimized, but time and labor required for adjustment increase
Solution Approach 1:
The patent implements a dynamic optical pulse stretching mechanism where the pulse width and waveform can be continuously adjusted by varying the delay amount between the reference light beam and the measurement light beam. This dynamic control eliminates the need for manual component replacement or adjustment, allowing real-time optimization of pulse parameters without time loss.
Solution Approach 2:
The patent enables parameter changes in the output pulse by modifying the delay amount parameter within the optical pulse stretcher. By changing this single parameter, the pulse width and waveform are automatically optimized without requiring physical adjustment of optical components, thus reducing adjustment time and labor while maintaining manufacturing precision.
3Manufacturing precision
If the polarization direction of the laser beam is not controlled, then the optical system is simpler, but chromatic aberration occurs and resolution decreases
Solution Approach 1:
The patent integrates polarization control functionality into the optical pulse stretcher system, which already serves the primary function of pulse stretching. By making the stretcher multi-functional (both pulse stretching and polarization control), the patent achieves resolution improvement without adding separate dedicated polarization control devices, thus minimizing the increase in optical system complexity.
Solution Approach 2:
The patent replaces complex mechanical polarization control mechanisms with an optical-based polarization management system using Faraday rotators and polarizers integrated into the pulse stretcher. This substitution reduces mechanical complexity while maintaining the ability to control polarization direction for chromatic aberration reduction and resolution improvement.
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 enables dynamic adjustment of pulse width and waveform without replacing components, improving flexibility and reducing the time and labor required for optimization, while maintaining high resolution and polarization purity.
Implementation Method 1
a first Faraday rotator including a first magnet and a first Faraday material and disposed on an optical path of the delay optical system to rotate a polarization direction of the pulse laser beam
Data Source
AI summary
An optical pulse stretcher that stretches a pulse width of a pulse laser beam includes a polarizer configured to separate a component in a specific polarization direction of the pulse laser beam that has entered, a delay optical system including a plurality of mirrors through which the pulse laser beam reflected by or transmitted through the polarizer is propagated; and a first Faraday rotator that includes a first magnet and a first Faraday material and is disposed on an optical path of the delay optical system to rotate a polarization direction of the pulse laser beam.