Ring Cavity Excimer Laser Minimizing ASE and Energy Loss
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Solution Overview
Problem
High power gas discharge laser systems for DUV light sources face challenges in maintaining beam quality and reducing ASE (Amplified Spontaneous Emission) while achieving high power output, particularly in immersion lithography and laser annealing applications, where existing technologies suffer from energy loss and unacceptable levels of ASE due to the use of oscillators with front and rear reflecting mirrors.
Innovation Solution
A multi-chamber laser system with a seed laser oscillator and a power ring amplification stage, utilizing a ring cavity configuration to minimize energy loss and ASE, by optimizing the seed laser chamber for beam parameters and amplifying these parameters in a power ring amplification stage with a 24% output coupler, reducing the required MO output energy and increasing amplification, thereby improving pulse-to-pulse stability and output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If oscillators with front and rear reflecting mirrors are used, then laser output power can be achieved, but energy loss and unacceptable levels of ASE occur
Solution Approach 1:
The patent extracts and removes the harmful rear reflecting mirror from the oscillator cavity, keeping only the front output coupler. This eliminates the energy loss associated with the rear mirror while maintaining laser output power through a simplified single-mirror configuration that reduces overall cavity losses.
Solution Approach 2:
The patent changes the oscillator cavity configuration from a traditional two-mirror resonator to a single-mirror setup with an output coupler having specific reflectivity parameters (20-40%). This parameter change optimizes the balance between maintaining sufficient oscillation for laser output and minimizing energy loss through the cavity.
2Power
If oscillators with front and rear reflecting mirrors are used, then laser output power can be achieved, but unacceptable levels of ASE occur
Solution Approach 1:
The patent removes the rear reflecting mirror that contributes to excessive ASE generation through multiple cavity round trips. By extracting this component, the system reduces the opportunities for spontaneous emission amplification while preserving the necessary oscillation path for coherent laser output through the front output coupler.
3Power
If high power output is achieved through amplification, then power requirements are met, but pulse-to-pulse stability deteriorates
Solution Approach 1:
The patent performs preliminary optimization of the oscillator chamber parameters (gas pressure, electrode spacing, output coupler reflectivity) to generate a stable seed beam with consistent pulse characteristics before amplification. This preliminary action ensures that the amplified output maintains pulse-to-pulse stability even at high power levels.
Solution Approach 2:
The patent implements feedback control mechanisms that monitor oscillator chamber conditions and adjust parameters to maintain stable seed beam generation. This feedback ensures consistent input to the amplification stage, thereby maintaining pulse-to-pulse stability in the final high-power output.
4Productivity
If amplification is increased to reduce MO output energy requirements, then system efficiency improves, but ASE levels increase
Solution Approach 1:
The patent converts the potential harm of high amplification (which could increase ASE) into a benefit by using a specially designed output coupler with optimized reflectivity (20-40%). This coupler allows sufficient feedback for efficient amplification while transmitting the amplified beam with minimal ASE contamination, effectively turning the amplification process into a beneficial element rather than a source of harm.
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 achieves higher output power with reduced ASE and improved pulse-to-pulse stability, extending the life of optical components and reducing the Cost of Consumables, while maintaining or increasing output power, thus addressing the limitations of existing systems in high power and broad band applications.
Implementation Method 1
a gas discharge excimer or molecular fluorine laser system
Implementation Method 2
an electrical discharge between a first pair of electrodes in the seed laser chamber and a second pair of electrodes in the amplification stage
Implementation Method 3
a line narrowing module receiving the electrical discharge and the laser output light beam pulses and reducing a bandwidth of the laser output light beam pulses
Data Source
AI summary
A method/apparatus may comprise operating a line narrowed pulsed excimer or molecular fluorine gas discharge laser system by using a seed laser oscillator to produce an output which may comprise a first gas discharge excimer or molecular fluorine laser chamber; a line narrowing module; a laser amplification stage which may comprise a ring power amplification stage; the method of operation may the steps of: selecting a differential timing between an electrical discharge between a pair of electrodes in the first laser chamber and in the second laser chamber which at the same time keeps ASE below a selected limit and the pulse energy of the laser system output light beam of pulses essentially constant.