Laser System with Coherence Busting for Lithography
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Solution Overview
Problem
Current high power gas discharge laser systems face challenges in achieving high average power and maintaining beam stability for applications like immersion lithography, due to limitations in pulse energy, pulse duration, and coherence issues, which hinder the advancement of photolithography and laser annealing processes.
Innovation Solution
A laser system comprising a solid state seed laser and a gas discharge laser amplifier with a coherence busting mechanism, utilizing a beam combiner and frequency converter to achieve higher power and reduced speckle effects, while maintaining angular distribution and minimizing ASE levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high power gas discharge laser systems are used to increase average power, then power output is improved, but beam stability deteriorates due to coherence issues and speckle effects
Solution Approach 1:
The patent divides the laser system into multiple independent laser sources (multi-chamber configuration) that operate in parallel. Each chamber generates a separate beam that is subsequently combined, allowing the system to achieve high average power while the independent operation of each chamber maintains beam stability and reduces coherence-related speckle effects.
Solution Approach 2:
The patent combines outputs from multiple laser chambers using beam combining techniques. This merging of multiple independent beams achieves the desired high power output while the incoherent combination reduces speckle effects and maintains beam stability, resolving the contradiction between power and stability.
2Power
If pulse energy is increased to improve power output, then power is improved, but manufacturing precision deteriorates due to coherence issues affecting lithography
Solution Approach 1:
By segmenting the laser system into multiple independent chambers, each operating at optimized pulse energy levels, the system achieves high total power output without the coherence issues that arise from single high-energy pulses. This segmentation maintains the precision required for lithography applications.
Solution Approach 2:
The patent uses multiple copies of the laser chamber design, each producing identical but independent beams. These copied chambers operate in parallel to achieve high power while the independence of each copy prevents coherence buildup that would degrade lithography precision.
3Power
If pulse duration is extended to increase average power, then power is improved, but beam stability deteriorates due to coherence control issues
Solution Approach 1:
The multi-chamber configuration allows each chamber to operate with optimized pulse durations that maintain coherence control. By distributing the total power across multiple shorter pulses from independent chambers, the system achieves high average power while maintaining beam stability and coherence control.
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 solution enables the production of high average power laser systems with improved beam stability and reduced speckle, enhancing the capabilities for immersion lithography and laser annealing by increasing power density and maintaining coherence control.
Implementation Method 1
a pulsed solid state seed laser providing seed laser pulses
Implementation Method 2
a gas discharge laser amplifier receiving and amplifying the seed laser pulses
Implementation Method 3
a coherence busting mechanism receiving either the seed laser pulses or the output of the amplifier gain medium and reducing the coherency of such pulses
Data Source
AI summary
A method/apparatus may comprise a laser light source which may comprise a solid state seed laser system producing a seed laser output having a nominal center wavelength at a pulse repetition rate; a first and a second gas discharge laser amplifier gain medium each operating at a pulse repetition rate less than that of the seed laser system; a beam divider providing each of the respective first and second amplifier gain mediums with seed laser output pulses; a frequency converter modifying the nominal center wavelength of the output of the seed laser to essentially the nominal center wavelength of the amplifier gain medium; a beam combiner combining the outputs of the respective amplifier gain mediums to provide a light source output having the pulse repetition rate of the seed laser; a coherence buster operating on either or both of the output of the seed laser or amplifier gain mediums.