Low-Z Cryogenic LPP Illuminator for Semiconductor Metrology
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Solution Overview
Problem
Current X-ray metrology systems face challenges in providing accurate and cost-effective X-ray illumination for semiconductor fabrication due to issues with debris mitigation, target replenishment, and high costs associated with using high atomic number elements like Tin and Xenon, which limit their availability and efficiency.
Innovation Solution
A low atomic number, cryogenic Laser Produced Plasma (LPP) X-ray illumination source is developed, using materials like Carbon, Oxygen, or Nitrogen, which are abundant and inexpensive, and employing a debris management system with directed buffer gas flow and magnetic fields to minimize contamination and optimize plasma stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high atomic number elements like Tin and Xenon are used as LPP targets, then X-ray emission intensity is improved, but debris contamination and target replenishment complexity increase
Solution Approach 1:
The patent changes the fundamental parameter of target material atomic number from high (Tin, Xenon) to low (Carbon, Oxygen, Nitrogen). This parameter change fundamentally alters the plasma generation mechanism and emission characteristics, enabling sufficient X-ray production from low-Z materials through optimized laser coupling and plasma conditions, thereby reducing debris contamination while maintaining measurement capability
Solution Approach 2:
The patent employs inexpensive, readily available low atomic number materials (Carbon, Oxygen, Nitrogen) as target materials instead of costly rare gases like Xenon or Tin. These materials can be continuously supplied in solid or gaseous form, eliminating the need for expensive gas recycling systems and reducing operational costs while maintaining sufficient X-ray emission for metrology applications
2Illumination intensity
If high atomic number elements like Tin and Xenon are used as LPP targets, then X-ray emission intensity is improved, but system cost increases
Solution Approach 1:
The patent replaces expensive rare gas targets (Xenon, Tin) with inexpensive, abundant materials (Carbon, Oxygen, Nitrogen). These low-Z materials are readily available and do not require costly recovery and recycling infrastructure, dramatically reducing both initial system cost and ongoing operational expenses while providing sufficient X-ray emission for semiconductor metrology
Solution Approach 2:
The patent extracts and eliminates the costly components of the LPP system - specifically the expensive rare gas targets and associated recycling infrastructure. By using inexpensive atmospheric gases or solid materials that can be continuously supplied, the system removes the need for complex gas management and recovery systems, simplifying the overall system architecture and reducing costs
3Illumination intensity
If high atomic number elements like Tin and Xenon are used as LPP targets, then X-ray emission intensity is improved, but target replenishment complexity increases
Solution Approach 1:
The patent adopts a continuous supply approach using inexpensive low-Z materials that can be readily replenished in solid or gaseous form. Instead of managing and recycling expensive rare gas targets, the system uses materials like Carbon, Oxygen, and Nitrogen that can be continuously supplied from simple reservoirs, dramatically simplifying the target replenishment mechanism and reducing system complexity
Solution Approach 2:
The patent enables self-replenishing target material supply through cryogenically cooled drums that automatically deposit fresh target material layers. The system uses the natural properties of low-Z materials to maintain continuous target availability without complex intervention, reducing operational complexity while sustaining high X-ray emission intensity
4Object-generated harmful factors
If low atomic number materials are used as LPP targets, then debris contamination is reduced, but X-ray emission intensity decreases
Solution Approach 1:
The patent optimizes multiple parameters to compensate for the lower inherent X-ray emission of low-Z materials: laser pulse duration and intensity are adjusted to maximize plasma temperature and radiation yield; plasma density and composition are controlled through target material selection and laser coupling optimization; emission spectrum characteristics are tuned to match detector sensitivity. These parameter optimizations enable sufficient X-ray intensity from low-Z targets while maintaining the debris reduction advantage
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 low atomic number, cryogenic LPP source provides high brilliance X-ray illumination with reduced lateral stability requirements and costs, enabling efficient and accurate measurement of semiconductor structural and material characteristics without the need for costly rare gas recycling systems.
Implementation Method 1
directing a pulse of laser light to a low atomic number, cryogenic target in the plasma chamber causes the target material to ionize to form plasma
Implementation Method 2
causes the target material to ionize to form plasma that emits an illumination light
Implementation Method 3
The cryogenically cooled drum has a surface coated with an amount of low atomic number target material
Implementation Method 4
replacement target material is deposited onto the surface of the drum in a liquid or gas phase. The deposited material freezes onto the surface of the drum
Implementation Method 5
employing a debris management system with directed buffer gas flow and magnetic fields to minimize contamination and optimize plasma stability
Data Source
AI summary
Methods and systems for generating X-ray illumination from a laser produced plasma (LPP) employing a low atomic number, cryogenic target are presented herein. A highly focused, short duration laser pulse is directed to a low atomic number, cryogenically frozen target, igniting a plasma. In some embodiments, the target material includes one or more elements having an atomic number less than 19. In some embodiments, the low atomic number, cryogenic target material is coated on the surface of a cryogenically cooled drum configured to rotate and translate with respect to incident laser light. In some embodiments, the low atomic number, cryogenic LPP light source generates multiple line or broadband X-ray illumination in a soft X-ray (SXR) spectral range used to measure structural and material characteristics of semiconductor structures. In some embodiments, Reflective, Small-Angle X-ray Scatterometry measurements are performed with a low atomic number, cryogenic LPP illumination source as described herein.