Excimer Laser Linewidth Control Using Chirped Seed Pulses
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Solution Overview
Problem
Current semiconductor exposure technologies face challenges in achieving narrow spectral linewidths for excimer laser light, leading to chromatic aberrations and decreased resolution due to wide spectral linewidths of KrF and ArF excimer laser apparatuses, which are difficult to control in single longitudinal mode semiconductor lasers.
Innovation Solution
A laser system comprising a semiconductor laser that oscillates in a single longitudinal mode, with a current controller and semiconductor optical amplifier to produce pulsed laser light, and a wavelength conversion system to generate ultraviolet light, along with a control section to adjust chirping for achieving a target spectral linewidth, allowing precise control of the spectral linewidth of excimer laser light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If KrF or ArF excimer laser apparatus is used as light source for exposure, then ultraviolet light with appropriate wavelength can be obtained, but spectral linewidth becomes wide causing chromatic aberrations and decreased resolution
Solution Approach 1:
The patent changes the spectral parameter of the laser light by using a line narrowing module (etalon or grating) within the laser resonator to reduce the spectral linewidth from 350-400 pm to a narrower range, thereby reducing chromatic aberrations and improving resolution while maintaining the ultraviolet wavelength capability
Solution Approach 2:
The patent introduces a line narrowing module as an intermediary element within the laser resonator system. This module acts as a mediator that selectively filters and narrows the spectral linewidth of the excimer laser light without changing the fundamental wavelength, thus resolving the contradiction between maintaining UV wavelength and reducing spectral width
2Manufacturing precision
If line narrowing module is added to gas laser apparatus to narrow spectral width, then chromatic aberrations are reduced, but device complexity increases
Solution Approach 1:
The line narrowing module serves multiple functions simultaneously: it narrows the spectral linewidth to reduce chromatic aberrations, maintains the laser oscillation stability, and works with both KrF and ArF excimer laser systems. This multi-functionality justifies the added complexity by providing comprehensive spectral control
3Manufacturing precision
If single longitudinal mode oscillation is used in semiconductor laser, then spectral linewidth is narrowed, but control difficulty increases
Solution Approach 1:
The patent implements feedback control mechanisms to monitor and maintain single longitudinal mode oscillation in the semiconductor laser. By using feedback to detect and correct deviations from single-mode operation, the system achieves narrow spectral linewidth while keeping the control process manageable and automated
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 enables precise control of the spectral linewidth of excimer laser light, reducing chromatic aberrations and improving resolution, while also suppressing stimulated Brillouin scattering in fiber amplifiers, thereby enhancing the efficiency and accuracy of the exposure process.
Implementation Method 1
a first semiconductor laser configured to oscillate in a single longitudinal mode
Implementation Method 2
a first current controller configured to control current caused to flow through the first semiconductor laser in such a way that first laser light outputted from the first semiconductor laser is caused to undergo chirping
Implementation Method 3
a first semiconductor optical amplifier configured to amplify the first laser light into first pulsed laser light
Implementation Method 4
a wavelength conversion system configured to convert in terms of a wavelength second pulsed laser light amplified by the first amplifier into third pulsed laser light of ultraviolet light
Implementation Method 5
an excimer amplifier configured to amplify the third pulsed laser light
Data Source
AI summary
In a laser system according to a viewpoint of the present disclosure, a first amplifier amplifies first pulsed laser light outputted from a first semiconductor laser system into second pulsed laser light, a wavelength conversion system converts the second pulsed laser light in terms of wavelength into third pulsed laser light, and an excimer amplifier amplifies the third pulsed laser light. The first semiconductor laser system includes a first current controller that controls current flowing through a first semiconductor laser in such a way that first laser light outputted from the first semiconductor laser is caused to undergo chirping and a first semiconductor optical amplifier that amplifies the first laser light into pulsed light. The laser system includes a control section that controls the amount of chirping performed on the first pulsed laser light in such a way that excimer laser light having a target spectral linewidth is achieved.