Microlithography Laser Pulse Timing for Speckle and Resonance Control
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Solution Overview
Problem
Existing microlithography projection exposure apparatuses face challenges in achieving high accuracy and throughput due to speckle patterns caused by spatial and temporal coherence of laser light sources, and limitations in increasing pulse energy and repetition rate, which can lead to optical component degradation and acoustic resonances.
Innovation Solution
An optical system with a laser light source controlled to vary the time period between successive light pulses, using a control unit to manipulate optical components and adjust trigger signals, thereby reducing speckle contrast and increasing repetition rate while avoiding resonances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pulse energy is increased to increase the output power of the laser light source, then the throughput is improved, but the radiation loading of optical components increases leading to degradation
Solution Approach 1:
The patent applies periodic action by using pulse stretching to extend the duration of laser pulses from nanoseconds to microseconds. This periodic extension of pulse duration reduces the peak power while maintaining the same energy delivery, thereby reducing radiation loading on optical components during high-throughput operation
Solution Approach 2:
The patent changes the temporal parameter of the laser pulses by stretching them in time. The pulse stretcher modifies the pulse width from short (nanosecond scale) to long (microsecond scale), which fundamentally changes the interaction dynamics between the laser light and optical components, reducing damage risk
2Productivity
If the repetition rate is increased to increase the output power of the laser light source, then the throughput is improved, but acoustic resonances occur leading to spectral bandwidth rising above acceptable measures
Solution Approach 1:
The patent uses periodic action in the form of pulse stretching to lengthen the time between peak power events. By extending each pulse duration, the effective repetition rate of high-intensity events is reduced, preventing acoustic resonances while maintaining the nominal repetition rate for throughput
Solution Approach 2:
The patent introduces dynamic control of the pulse temporal profile through the pulse stretcher. The system dynamically adjusts the pulse duration to optimize the balance between throughput (repetition rate) and precision (spectral bandwidth control), preventing resonance conditions
3Reliability
If optical pulse stretchers are used to stretch pulse length to reduce degradation of downstream optical components, then the reliability is improved, but the structural space restrictions and decreasing output power limit the stretching
Solution Approach 1:
The patent fundamentally changes the temporal parameter of the laser pulses by stretching them in time from nanoseconds to microseconds. This parameter change reduces the peak power density, thereby reducing radiation loading and degradation of optical components without requiring complex spatial arrangements
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 effectively reduces speckle patterns, improves overlay accuracy, and enhances throughput by varying the time period between light pulses, thus optimizing the laser light source's performance.
Implementation Method 1
a laser light source for generating a multiplicity of light pulses
Implementation Method 2
an effect that can occur with regard to the desired accuracy properties to be satisfied inter alia during operation of the laser light sources mentioned above is the occurrence of what are known as speckle patterns, which are attributable to the spatial and temporal coherence of the generated light
Data Source
AI summary
An optical system, in particular for microlithography, comprises a laser light source for generating a multiplicity of light pulses, and a control unit configured to control the laser light source in such a way that, for a light pulse sequence generated by the laser light source, the time period between respectively successive light pulses varies across the light pulse sequence. A method comprises operating the optical system.