Monolithic Bandwidth Narrowing Apparatus for DUV Laser Inspection
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Solution Overview
Problem
Existing DUV lasers face challenges in reducing bandwidth while maintaining other laser parameters, as existing methods are invasive, lead to power losses, and increase complexity, making them unsuitable for high-speed semiconductor inspection applications.
Innovation Solution
The method involves dividing fundamental laser light pulses into sub-pulses, stretching and adding opposite chirps using monolithic optical devices like chirped volume Bragg gratings, and recombining them to produce sum frequency light with a narrower bandwidth, avoiding intra-cavity devices to maintain laser efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If intra-cavity bandwidth limiting devices (etalon, birefringent filter, optical grating) are used to reduce laser bandwidth, then the bandwidth is reduced, but power losses increase and system complexity increases
Solution Approach 1:
The patent extracts the bandwidth limiting function from the intra-cavity region and relocates it to the post-cavity region using optical spectral shaping devices. This allows bandwidth control without the harmful effects of intra-cavity devices, eliminating power losses and complexity associated with traditional approaches.
Solution Approach 2:
The patent introduces optical spectral shaping devices (gratings, prisms, or etalons) as intermediary components in the post-cavity region. These devices act as mediators to shape the spectral bandwidth of the laser output without requiring direct intra-cavity intervention, thereby avoiding power losses and system complexity.
2Manufacturing precision
If intra-cavity bandwidth limiting devices are used to reduce laser bandwidth, then the bandwidth is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the bandwidth limiting function from the intra-cavity region and relocates it to the post-cavity region using optical spectral shaping devices. This allows bandwidth control without the harmful effects of intra-cavity devices, eliminating power losses and complexity associated with traditional approaches.
Solution Approach 2:
The patent introduces optical spectral shaping devices (gratings, prisms, or etalons) as intermediary components in the post-cavity region. These devices act as mediators to shape the spectral bandwidth of the laser output without requiring direct intra-cavity intervention, thereby avoiding power losses and system complexity.
3Manufacturing precision
If conventional bandwidth reduction methods are used, then bandwidth is reduced, but laser efficiency decreases and stability deteriorates
Solution Approach 1:
The patent extracts the bandwidth limiting function from the intra-cavity region and relocates it to the post-cavity region using optical spectral shaping devices. This allows bandwidth control without the harmful effects of intra-cavity devices, eliminating power losses and complexity associated with traditional approaches.
Solution Approach 2:
The patent introduces optical spectral shaping devices (gratings, prisms, or etalons) as intermediary components in the post-cavity region. These devices act as mediators to shape the spectral bandwidth of the laser output without requiring direct intra-cavity intervention, thereby avoiding power losses and system complexity.
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 the bandwidth of DUV lasers without redesigning the oscillator cavity, maintaining high efficiency and stability, and is suitable for high-speed semiconductor inspections by generating sum frequency output with minimal power loss.
Implementation Method 1
Each sub-pulse is directed onto a different surface of a single monolithic device to generate two stretched sub-pulses with opposite chirps
Implementation Method 2
The two stretched sub-pulses are mixed to produce sum frequency pulses having a bandwidth that is narrower than the bandwidth of the fundamental laser light pulses
Data Source
AI summary
A pulsed UV laser assembly includes a partial reflector or beam splitter that divides each fundamental pulse into two sub-pulses and directs one sub-pulse to one end of a Bragg grating and the other pulse to the other end of the Bragg grating (or another Bragg grating) such that both sub-pulses are stretched and receive opposing (positive and negative) frequency chirps. The two stretched sub-pulses are combined to generate sum frequency light having a narrower bandwidth than could be obtained by second-harmonic generation directly from the fundamental. UV wavelengths may be generated directly from the sum frequency light or from a harmonic conversion scheme incorporating the sum frequency light. The UV laser may further incorporate other bandwidth reducing schemes. The pulsed UV laser may be used in an inspection or metrology system.