Coherence Reduction Optical System for Laser Speckle Control
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Solution Overview
Problem
Current ArF excimer laser systems for semiconductor lithography face challenges in coherence reduction of pulsed laser light, leading to unwanted speckle patterns that can affect exposure processing precision.
Innovation Solution
Incorporating a coherence reduction optical system, such as a random phase plate or wedge substrate, between the master oscillator and amplifier stages, controlled to vary the speckle distribution of pulsed laser light, thereby reducing coherence and minimizing speckle interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a coherence reduction optical system is introduced to reduce speckle patterns, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
A coherence reduction optical system is introduced as an intermediary component between the laser source and the exposure system. This mediator reduces the coherence of laser light, thereby suppressing speckle patterns while maintaining the overall system architecture. The intermediary approach allows speckle reduction without fundamentally redesigning the entire laser system.
Solution Approach 2:
The coherence reduction optical system changes the coherence parameter of the laser light by introducing controlled phase variations. By modifying the coherence parameter through optical elements such as rotating diffusers or phase plates, the system reduces speckle patterns while preserving the laser's intensity and wavelength characteristics.
2Manufacturing precision
If speckle reduction is achieved through coherence reduction, then exposure processing precision is improved, but loss of time occurs due to additional optical processing
Solution Approach 1:
The coherence reduction optical system employs periodic action through rotating diffusers or moving phase plates that continuously change the speckle pattern at high speed. This periodic modulation averages out the speckle patterns over time, achieving speckle reduction without requiring multiple sequential processing steps, thus minimizing time loss.
Solution Approach 2:
The system maintains continuous useful action by implementing coherence reduction in a single-pass configuration where the laser beam passes through the coherence reduction optical system once. This continuous single-pass approach avoids multiple reflections or sequential processing steps that would increase time loss while still achieving effective speckle suppression.
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 effectively reduces speckle patterns in the pulsed laser light, enhancing the precision and consistency of exposure processing in semiconductor lithography by averaging speckle distributions across the laser beam.
Implementation Method 1
a coherence reduction optical system configured to reduce coherence of the pulsed laser light from the master oscillator
Data Source
AI summary
A laser system in this disclosure may include: a master oscillator configured to output pulsed laser light, a coherence reduction optical system configured to reduce coherence of the pulsed laser light from the master oscillator, and a controller configured to control the coherence reduction optical system so that a speckle of the pulsed laser light varies.