SBO and LBO Crystal Waveguides for High-Power DUV Conversion
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Solution Overview
Problem
Current DUV and VUV frequency conversion crystals face challenges such as low damage thresholds, hygroscopicity, absorption issues, and lack of large birefringence, making them unsuitable for high-power VUV/DUV light generation and semiconductor inspection applications.
Innovation Solution
The use of strontium tetraborate (SBO) and lithium triborate (LBO) nonlinear crystal waveguides, configured for quasi-phase matching, to generate DUV radiation between 120-200 nm, overcoming limitations of existing crystals by providing high power and transparency in the VUV range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional crystals (BBO, CLBO) are used for DUV frequency conversion, then UV light can be generated, but the damage threshold is low and absorption increases for wavelengths below 190-200 nm
Solution Approach 1:
The patent changes the material parameter by selecting SBO and LBO crystals with specific optical properties (transparency down to 120 nm, high damage threshold) instead of conventional BBO or CLBO crystals. This material substitution resolves the contradiction by maintaining light generation capability while significantly improving damage threshold and reducing absorption at wavelengths below 200 nm.
2Reliability
If CLBO crystal is used for frequency conversion, then higher damage threshold is achieved, but the crystal is hygroscopic requiring great care during handling and processing
Solution Approach 1:
The patent extracts the hygroscopic property from the system by selecting SBO and LBO crystals that are non-hygroscopic. This removes the handling and processing complications associated with CLBO while maintaining the high damage threshold benefit, thus resolving the contradiction between reliability and ease of operation.
3Measurement precision
If high average power illumination is used for detecting small particles, then detection sensitivity improves, but peak power damage to optics and samples increases
Solution Approach 1:
The patent employs pulsed laser operation with high repetition rates (mode-locked lasers) to deliver high peak power in short bursts followed by cooling periods. This periodic action allows accumulation of sufficient energy for sensitive detection while preventing continuous overheating and damage to optics and samples, resolving the contradiction between measurement precision and harmful factors.
4Reliability
If continuous wave (CW) light source is used for inspection, then constant power level avoids damage issues, but peak power is insufficient for efficient frequency conversion
Solution Approach 1:
The patent transitions from CW to pulsed operation with high repetition rates, creating a periodic action that delivers high peak power during pulses while maintaining acceptable average power levels. This resolves the contradiction by providing sufficient peak power for efficient frequency conversion in SBO/LBO crystals while avoiding continuous damage through the periodic duty cycle.
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 SBO and LBO waveguides enable efficient generation of high-power DUV light suitable for semiconductor inspection and metrology, avoiding the drawbacks of prior art crystals, with improved damage thresholds and transparency.
Implementation Method 1
a first fundamental laser configured to generate a fundamental laser beam having a corresponding fundamental frequency and a fundamental wavelength between 720 nm and 800 nm; and two or more frequency doubling stages, the two or more frequency doubling stages including at least an intermediate frequency doubling stage and a final frequency doubling stage, the intermediate frequency doubling stage is configured to receive the first fundamental frequency and generate a second harmonic light having a second harmonic frequency
Implementation Method 2
a nonlinear crystal waveguide configured to phase match or quasi-phase-match the second harmonic frequency and the laser output light
Data Source
AI summary
A system for frequency conversion is disclosed. The system includes a nonlinear crystal waveguide formed from strontium tetraborate (SBO) or lithium triborate (LBO). This system is used for second harmonic generation or sum-frequency generation to produce laser output light having wavelengths in the range of about 120-200 nm. Inspection systems, lithography systems and cutting systems incorporating the frequency conversion system are also described.