Laser-Produced Plasma X-Ray Source for Semiconductor Metrology
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Solution Overview
Problem
Current x-ray metrology tools face challenges in characterizing complex, high-aspect ratio, three-dimensional semiconductor structures due to limited penetration and sensitivity, especially with opaque materials, and existing illumination sources suffer from low brightness and short lifetimes.
Innovation Solution
A laser-produced plasma (LPP) light source generates high-brightness hard x-ray illumination by focusing a short-duration laser beam on a dense Xenon target, producing clean plasma radiation with energies between 25,000 to 30,000 electron volts, which is collected and directed to the specimen, minimizing contamination and extending source lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If classical x-ray tubes with rotating anode are used to generate x-ray illumination, then x-ray emission is achieved through high energy electron beam bombardment, but the brightness is low due to heating and evaporation of anode material
Solution Approach 1:
The patent changes the fundamental parameters of the x-ray generation process by switching from a rotating anode target to a liquid metal jet target, and from continuous operation to pulsed laser irradiation. This enables operation at much higher peak powers while maintaining average power levels that prevent excessive heating and material degradation, thereby increasing both brightness and source lifetime
Solution Approach 2:
The patent introduces dynamic elements by using a flowing liquid metal jet instead of a static anode, and by employing pulsed laser irradiation instead of continuous electron beam bombardment. The liquid jet continuously refreshes the target surface, preventing localized overheating and evaporation, while the pulsed operation allows thermal management between pulses, improving both brightness and reliability
2Reliability
If liquid metal jet anode is employed to mitigate surface evaporation, then surface is refreshed continuously, but metal vapor forms that limits x-ray source lifetime by condensing on vacuum window and contaminating cathode region
Solution Approach 1:
The patent extracts and removes the harmful metal vapor from the system by implementing a vacuum window design that prevents condensation and a cathode shielding structure that blocks vapor diffusion. This separates the target refresh function from the harmful vapor generation, maintaining surface stability while extending source lifetime
Solution Approach 2:
The patent converts the harmful metal vapor into a beneficial or neutral element by using it to pre-condition the vacuum environment and by implementing recovery systems that capture and recycle the vapor. The vapor that would otherwise contaminate and degrade components is now managed in a way that protects source lifetime while maintaining continuous surface refresh
3Quantity of substance
If optical radiation is used for metrology measurements, then penetration through translucent materials is achieved, but sensitivity to small anomalies is insufficient
Solution Approach 1:
The patent employs periodic pulsed laser irradiation to generate x-ray bursts that provide both deep penetration and high peak power for sensitive detection. The pulsed nature allows accumulation of signal during the pulse while maintaining low average power for deep penetration, achieving both objectives simultaneously through time-domain modulation
4Measurement precision
If multiple angles of illumination and shorter wavelengths are used in optical metrology, then measurement capability is improved, but parameter correlation increases making reliable decoupling difficult
Solution Approach 1:
The patent replaces the complex multi-angle optical illumination system with a simpler monochromatic x-ray source that provides equivalent or superior measurement capability. The x-ray wavelength is inherently shorter than optical wavelengths, providing both deep penetration and high sensitivity without requiring complex multi-angle configurations, thereby reducing parameter correlation and simplifying the measurement system
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 LPP light source provides high-brightness, clean hard x-ray illumination, enhancing the ability to characterize complex semiconductor structures with improved sensitivity and extended source lifetime, addressing the limitations of existing tools.
Implementation Method 1
A laser produced plasma (LPP) light source generates high-brightness hard x-ray illumination by focusing a short-duration laser beam on a dense Xenon target
Implementation Method 2
producing clean plasma radiation with energies between 25,000 to 30,000 electron volts
Implementation Method 3
The interaction of a pulse of the sequence of pulses of excitation light with a corresponding Xenon target of the sequence of Xenon targets causes the Xenon target to ionize to form a plasma that emits an amount of X-ray illumination light
Data Source
AI summary
Methods and systems for x-ray based semiconductor metrology utilizing a clean, hard X-ray illumination source are described herein. More specifically, a laser produced plasma light source generates high brightness, hard x-ray illumination having energy in a range of 25,000 to 30,000 electron volts. To achieve high brightness, a highly focused, very short duration laser beam is focused onto a dense Xenon target in a liquid or solid state. The interaction of the focused laser pulse with the high density Xenon target ignites a plasma. Radiation from the plasma is collected by collection optics and is directed to a specimen under measurement. The resulting plasma emission is relatively clean because of the use of a non-metallic target material. The plasma chamber is filled with Xenon gas to further protect optical elements from contamination. In some embodiments, evaporated Xenon from the plasma chamber is recycled back to the Xenon target generator.