Brewster Angle Frequency Conversion System for High Power DUV
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Solution Overview
Problem
Current semiconductor wafer and photomask inspection systems face challenges in achieving high throughput and resolution due to the limitations of conventional lasers used for deep ultraviolet (DUV) light generation, which require high power, short wavelength, and stable performance, but are hindered by the degradation of optical coatings under high power illumination, leading to short lifetimes and low damage thresholds.
Innovation Solution
A frequency conversion system with a high damage threshold is implemented, utilizing multiple stages of frequency conversion, Brewster angle dual wavelength waveplates, and Brewster angle-total internal reflection harmonic separation elements to generate high power DUV light without optical coatings, enhancing stability and reducing stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional lasers with optical coatings are used for DUV light generation, then high power output is achieved, but the optical coatings degrade under high power illumination leading to short lifetime
Solution Approach 1:
The patent removes optical coatings from the frequency conversion system by using Brewster angle incidence for all optical elements. This extraction of the problematic component (optical coatings) eliminates the degradation issue while maintaining high power DUV light generation through the use of Brewster angle waveplates, Brewster angle mirrors, and Brewster angle output windows that rely on polarization rather than coatings.
2Power
If optical coatings are used in UV-DUV frequency conversion system, then power handling is improved, but maintenance frequency increases due to coating degradation
Solution Approach 1:
The system uses Brewster angle incidence which inherently provides polarization-dependent reflection and transmission without requiring protective coatings. The Brewster angle waveplates and mirrors self-regulate the polarization state of light, eliminating the need for coating maintenance while maintaining high power handling capability throughout the system's operational life.
3Power
If conventional frequency conversion crystals are used, then DUV light generation is achieved, but system size is large and damage threshold is low
Solution Approach 1:
The patent combines multiple frequency conversion crystals (BBO, LBO, KTP) in a cascaded configuration where each crystal performs a specific conversion step (e.g., 1064nm to 532nm, 532nm to 266nm, 266nm to 193nm). This merging of multiple conversion stages into a single integrated system achieves compact DUV light generation while using the Brewster angle configuration to maintain high damage threshold throughout the conversion chain.
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 system achieves extended lifetime, reduced maintenance, and increased reliability of the laser, with improved power handling and reduced system size, while maintaining high efficiency and stability over time.
Implementation Method 1
a dual wavelength Brewster angle waveplate configured to receive first alternate wavelength light and second alternate wavelength light emanating from the second nonlinear optical crystal, the dual wavelength Brewster angle waveplate further configured to rotate a polarization of the first alternate wavelength light relative to the second alternate wavelength light such that the first alternate wavelength light and the second alternate wavelength light have substantially the same polarization
Implementation Method 2
a first nonlinear optical crystal configured to receive fundamental laser light from the fundamental laser light source, the first optical crystal configured to generate first alternate wavelength light by frequency converting at least a portion of the received fundamental laser light to first alternate wavelength light
Implementation Method 3
a harmonic separator configured to receive the first alternate wavelength light and the second alternate wavelength light from the set of Brewster angle wavefront processing optics, the harmonic separator configured to at least partially separate the first alternate wavelength light from the second alternate wavelength light
Data Source
Figure 1
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Figure 3A
AI summary
The present invention includes a fundamental laser light source configured to generate fundamental wavelength laser light, a first nonlinear optical crystal configured to generate first alternate wavelength light; a second nonlinear optical crystal configured to generate second alternate wavelength light; a dual wavelength Brewster angle waveplate configured to rotate a polarization of the first alternate wavelength light relative to the second alternate wavelength light such that the first and second alternate wavelength light have the same polarization; a set of Brewster angle wavefront processing optics configured to condition the first and second alternate wavelengths of light; a harmonic separator configured to separate the first alternate wavelength light from the second alternate wavelength light; and a Brewster angle output window configured to transmit the first or second alternate wavelengths of light from the interior of a laser frequency conversion system to the exterior of the laser frequency conversion system.