Tunable DUV Laser Assembly for Multi-Wavelength Defect Detection
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Solution Overview
Problem
Conventional DUV laser assemblies are limited to generating a single wavelength, failing to detect or accurately identify defects on semiconductor wafers and reticles, and require high peak power levels that can cause damage to optics and samples, while existing tunable lasers are expensive, inefficient, or use toxic gases.
Innovation Solution
A tunable laser assembly using a fan-out periodically poled nonlinear crystal and interchangeable nonlinear summing crystals, controlled by a frequency system, generates DUV light at two or more wavelengths between 184 nm and 200 nm, allowing for adjustable output frequencies to enhance defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single wavelength DUV laser is used, then the device complexity is reduced, but the measurement precision for detecting defects is insufficient
Solution Approach 1:
The laser assembly enables dynamic wavelength tuning between 184 nm and 200 nm through adjustable optical elements (prisms, gratings, or tunable lasers), allowing the system to adapt to different defect detection requirements. This dynamic capability resolves the contradiction by providing multiple wavelengths on demand rather than requiring fixed multi-wavelength laser assemblies.
Solution Approach 2:
The system changes the wavelength parameter of the DUV light to optimize defect detection for different particle sizes and defect types. By tuning the wavelength within the 184-200 nm range, the system achieves high measurement precision without requiring complex multi-wavelength laser sources, as the same laser can be tuned to different wavelengths as needed.
2Illumination intensity
If high peak power levels are used, then the illumination intensity for detecting small particles is improved, but the object-generated harmful factors (damage to optics and samples) increase
Solution Approach 1:
The system uses pulsed laser operation with optimized pulse duration and repetition rate to deliver high peak power for scattering signal generation while allowing sufficient cooling time between pulses. This periodic action enables high illumination intensity for detecting sub-wavelength particles without causing thermal damage to optics or samples, resolving the contradiction between signal strength and damage prevention.
Solution Approach 2:
The system optimizes the temporal parameters (pulse width, repetition rate, duty cycle) and spectral parameters (wavelength) of the DUV light to achieve the right balance. By changing these parameters, the system can deliver sufficient peak power for detection while controlling average power to prevent damage, resolving the contradiction between illumination intensity and harmful effects.
3Adaptability or versatility
If multiple fixed wavelength lasers are used, then the adaptability for detecting different defect types is improved, but the device complexity and cost increase
Solution Approach 1:
The laser assembly is designed to perform multiple defect detection functions using a single tunable DUV source. By enabling wavelength tuning within the 184-200 nm range, the system can detect various defect types (particles, scratches, pattern defects) with different scattering characteristics, achieving versatility without requiring multiple specialized laser sources.
Solution Approach 2:
The system employs dynamic wavelength tuning capabilities through adjustable optical elements that allow real-time adjustment of the DUV wavelength. This dynamic adaptability enables the same laser assembly to optimize detection for different defect types and sizes, providing versatility equivalent to multiple fixed-wavelength lasers but with reduced complexity and cost.
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 tunable laser assembly enhances defect detection by maximizing contrast between defects and surrounding patterns, improving inspection accuracy and reducing damage risk through adjustable wavelengths.
Implementation Method 1
an optical parametric system (OPS) that is configured to circulate the down-converted frequency through the fan-out PPNLC to further enhance the power of the down-converted light
Implementation Method 2
a set of nonlinear summing crystals that are operably controlled by a frequency control system to generate laser output light having an output frequency that is the sum of the fifth harmonic frequency and the down-converted frequency
Implementation Method 3
one or more fundamental lasers to generate fundamental light having a wavelength between about 1 μm and 1.1 μm
Data Source
AI summary
A tunable laser assembly uses a fundamental wavelength between 1 μm and 1.1 μm to alternately generate laser output light at two or more output wavelengths within the range of 184 nm to 200 nm by directing the fundamental light through different regions of a fan-out periodically poled nonlinear crystal to generate corresponding different down-converted signals, and using different nonlinear summing crystals to mix the different down-converted signals with a fifth harmonic of the fundamental wavelength. Each nonlinear summing crystal has a crystal axis aligned at an angle relative to the light propagation direction to facilitate the efficient transmission and summing of the fifth harmonic with an associated down-converted signal. In response to a user-selected output wavelength, a frequency control system positions the fan-out periodically poled nonlinear crystal to generate a corresponding down-converted signal frequency and positions an associated nonlinear summing crystal to receive the fifth harmonic and the corresponding down-converted signal.