X-ray Multilayer Mirror for Depth-Resolved Metrology
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Solution Overview
Problem
Current X-ray reflectometry (XRR) techniques face challenges in providing adequate depth resolution and elemental specificity for 3D semiconductor architectures, particularly in detecting buried layers and small quantities of dopants and dielectric materials, due to limitations in signal strength and interference from substrate materials, which hinders efficient process monitoring in semiconductor manufacturing.
Innovation Solution
The method involves generating an x-ray beam with a specific energy bandwidth and collimation, irradiating the sample at varied incidence angles, and simultaneously detecting reflected x-rays and x-ray fluorescence or photoelectrons to enhance depth resolution and material specificity, using x-ray sources with multiple generating materials to optimize x-ray energy for characteristic fluorescence production and reduce background interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional XRR techniques are used, then penetration to detect structures beneath the surface is achieved, but depth resolution and elemental specificity are insufficient
Solution Approach 1:
The x-ray beam is segmented into multiple discrete energy components through the use of a multilayer mirror with alternating high-Z and low-Z layers. Each layer pair reflects a specific energy range, allowing the beam to be divided into multiple energy bands that can be independently optimized for different depth resolutions and elemental specificities.
Solution Approach 2:
Different regions of the multilayer mirror structure are designed with locally optimized properties - specific layer thicknesses and materials are selected to reflect particular x-ray energies. This allows different parts of the beam to have different energy characteristics, enabling simultaneous optimization for both depth resolution and elemental specificity in different spatial regions.
2Measurement precision
If x-ray energy is increased to detect small quantities of dopants and dielectric materials, then signal strength improves, but background interference from substrate materials increases
Solution Approach 1:
The multilayer mirror structure employs asymmetric layering with alternating high-Z and low-Z materials in specific thickness ratios. This asymmetric configuration creates selective reflection characteristics that enhance sensitivity to specific elements while suppressing background signals from substrate materials, as the reflection coefficients are tuned to match the atomic number differences between dopants and the substrate.
Solution Approach 2:
The patent converts the harmful background interference from substrate materials into a beneficial signal by selecting x-ray energies that exploit the atomic number contrast between dopants/dielectrics and the substrate. The multilayer mirror is designed to reflect energies where the substrate has low absorption, transforming what would be background noise into a clean signal for detecting small quantities of materials.
3Productivity
If data collection time is reduced for faster process monitoring, then productivity improves, but signal-to-noise ratio deteriorates
Solution Approach 1:
The multilayer mirror is pre-configured with optimized layer thicknesses and materials that are calculated in advance to maximize reflection at specific energies. This preliminary optimization of the mirror structure eliminates the need for lengthy data collection to achieve sufficient signal strength, as the beam is pre-conditioned to have maximum intensity at the required energies, enabling fast process monitoring with high signal-to-noise ratio.
Solution Approach 2:
The patent changes the energy parameters of the x-ray beam by using the multilayer mirror to select specific energy ranges. By adjusting the layer thicknesses and materials of the mirror, the beam energy can be optimized for different measurement requirements, allowing rapid switching between different detection modes without requiring long data collection times, thus maintaining both productivity and measurement precision.
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
This approach improves the depth-wise measurement sensitivity to 0.1 nm or less for atomic elements, increases signal-to-noise ratio, and enables faster process monitoring by reducing data collection time, effectively addressing the limitations of previous XRR techniques.
Implementation Method 1
detecting x-ray fluorescence x-rays and/or photoelectrons from the sample
Implementation Method 2
detecting x-ray fluorescence x-rays and/or photoelectrons from the sample
Implementation Method 3
X-ray reflectivity (XRR) is a useful technique to characterize surfaces and interfaces
Implementation Method 4
The first x-ray beam is collimated to have a first collimation angular range less than 7 mrad
Data Source
AI summary
A system and method for analyzing a three-dimensional structure of a sample includes generating a first x-ray beam having a first energy bandwidth less than 20 eV at full-width-at-half maximum and a first mean x-ray energy that is in a range of 1 eV to 1 keV higher than an absorption edge energy of a first atomic element of interest, and that is collimated to have a collimation angular range less than 7 mrad in at least one direction perpendicular to a propagation direction of the first x-ray beam; irradiating the sample with the first x-ray beam at a plurality of incidence angles relative to a substantially flat surface of the sample, the incidence angles of the plurality of incidence angles in a range of 3 mrad to 400 mrad; and simultaneously detecting a reflected portion of the first x-ray beam from the sample and detecting x-ray fluorescence x-rays and/or photoelectrons from the sample.