Multilayer Calibration Targets for X-ray Metrology Alignment
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Solution Overview
Problem
Current X-ray metrology systems face challenges in accurately measuring critical dimensions and overlay of semiconductor structures due to penetration issues with complex 3D geometries and opaque materials, leading to sensitivity losses and correlation problems, especially with high-aspect ratio structures and small feature sizes.
Innovation Solution
The development of multilayer calibration targets with high diffraction efficiency, manufactured using standard optical and semiconductor fabrication techniques, enables fast and accurate alignment and calibration of X-ray based measurement systems by directly measuring flux and photon leakage, and aligning the sample and X-ray beam in all degrees of freedom.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If longer wavelengths (e.g., near infrared) are employed to penetrate deep into 3D FLASH device structures, then penetration depth is improved, but sensitivity to small anomalies decreases and parameter correlation increases
Solution Approach 1:
The patent segments the measurement process by using multiple illumination wavelengths instead of a single wavelength. Shorter wavelengths (e.g., visible light) provide high sensitivity for surface and near-surface features, while longer wavelengths (e.g., near infrared) penetrate deeper into the structure. This segmentation allows each wavelength to optimize for specific depth ranges, resolving the contradiction between penetration depth and sensitivity.
Solution Approach 2:
The patent adds the wavelength dimension to the measurement approach by employing broadband illumination covering multiple spectral regions. This dimensional expansion allows simultaneous optimization of both penetration depth (achieved through longer wavelengths) and sensitivity to small anomalies (achieved through shorter wavelengths), transforming a single-parameter optimization problem into a multi-parameter solution.
2Measurement precision
If multiple angles of illumination and shorter wavelengths are used to improve measurement sensitivity, then sensitivity is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent employs a single broadband illumination source that inherently provides multiple wavelengths, eliminating the need for separate light sources for different wavelength ranges. This universal source approach maintains measurement sensitivity across different depth regions while significantly reducing system complexity compared to using multiple specialized sources.
Solution Approach 2:
The patent changes the spectral parameter of the illumination by using a broadband source that naturally emits across a wide wavelength range. This parameter change allows the system to access both short and long wavelengths without adding mechanical complexity, achieving high sensitivity measurements while keeping the illumination system relatively simple.
3Length of stationary object
If X-ray reflectometers are used to achieve penetration into high aspect ratio structures, then penetration capability is improved, but alignment precision and measurement accuracy deteriorate due to limited calibration targets
Solution Approach 1:
The patent applies preliminary action by fabricating multilayer calibration targets with precisely controlled layer thicknesses and compositions before performing X-ray measurements. These pre-fabricated targets with known geometries enable accurate calibration of the X-ray reflectometer, establishing a reference framework that improves alignment precision and measurement accuracy before actual device characterization.
Solution Approach 2:
The patent introduces multilayer calibration targets as intermediary objects between the X-ray source and the device under test. These targets serve as mediators that provide known scattering and reflectivity patterns, enabling the system to calibrate and verify alignment precision without directly measuring the complex high aspect ratio structures.
4Adaptability or versatility
If destructive sample preparation techniques such as FIB machining are used to enable TEM measurement of arbitrary depths, then measurement capability is improved, but measurement time and cost increase significantly
Solution Approach 1:
The patent applies self-service by using X-ray scattering and reflectivity measurements that can penetrate and characterize high aspect ratio structures directly through the wafer backside without requiring physical sectioning or preparation. The measurement system itself provides the capability to access arbitrary depths non-destructively, eliminating the need for time-consuming FIB machining and TEM sample preparation steps.
Solution Approach 2:
The patent replaces mechanical sample preparation (FIB machining, sectioning) with non-mechanical X-ray based measurement techniques. Instead of physically cutting and preparing samples for TEM, the system uses X-ray scattering and reflectivity to obtain depth-resolved structural information, substituting a mechanical process with a non-contact, non-destructive physical measurement approach.
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 solution allows for precise navigation and measurement of small features with improved accuracy, reducing measurement times and errors, and is cost-effective with rapid production capabilities.
Implementation Method 1
X-rays incident on the multilayer target are diffracted into a zeroth order beam and multiple higher order diffraction orders
Data Source
AI summary
Multilayer targets enabling fast and accurate, absolute calibration and alignment of X-ray based measurement systems are described herein. The multilayer calibration targets have very high diffraction efficiency and are manufactured using fast, low cost production techniques. Each target includes a multilayer structure built up with pairs of X-ray transparent and X-ray absorbing materials. The layers of the multilayer target structure is oriented parallel to an incident X-ray beam. Measured diffraction patterns indicate misalignment in position and orientation between the incident X-Ray beam and the multilayer target. In another aspect, a composite multilayer target includes at least two multilayer structures arranged adjacent one another along a direction aligned with the incident X-ray beam, adjacent one another along a direction perpendicular to the incident X-ray beam, or a combination thereof. In some embodiments, the multilayer structures are spatially separated from one another by a gap distance.