X-ray Reflectivity Thickness Measurement for Complex Semiconductor Structures
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Solution Overview
Problem
Existing methods for measuring the thickness of semiconductor devices, such as spectroscopic ellipsometry, face challenges with complex multi-layer structures and materials that are difficult to express mathematically, leading to inaccurate thickness measurements due to high correlation between thin layers and changes in physical properties during manufacturing processes.
Innovation Solution
A method involving the measurement of X-ray reflectivity before and after forming an object on a substrate, using fast-Fourier transform to calculate variations in reflectivity spectra, and determining thickness based on these transformations, which reduces the influence of dispersive and absorptive terms and minimizes errors in complex structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spectroscopic ellipsometry is used to measure thickness, then high resolution is achieved, but measurement accuracy deteriorates for complex multi-layer structures
Solution Approach 1:
The patent segments the measurement process into two distinct stages: first measuring the substrate's X-ray reflectivity spectrum before object formation, then measuring the combined substrate-object spectrum after formation. By subtracting these two spectra, the method isolates the object's contribution, effectively segmenting the complex multi-layer measurement into manageable parts and eliminating the influence of underlying layers.
Solution Approach 2:
The patent extracts the object's thickness information by removing the substrate's contribution from the total measurement. Through spectral subtraction and fast-Fourier transform, the method extracts only the relevant object characteristics from the complex multi-layer spectrum, discarding the dispersive and absorptive terms of the substrate that cause measurement errors.
2Measurement precision
If spectroscopic ellipsometry is used, then thickness can be measured, but errors increase due to high correlation between thin layers
Solution Approach 1:
The measurement is divided into substrate-only measurement and substrate-with-object measurement. This segmentation breaks the high correlation between layers by measuring the substrate separately, allowing the object's thickness to be determined independently of the substrate's complex multi-layer structure.
Solution Approach 2:
The object's thickness information is extracted by removing the substrate's spectral contribution. The fast-Fourier transform of the subtracted spectrum isolates the object's thickness parameter, eliminating the corrupting influence of layer correlations present in the total spectrum.
3Adaptability or versatility
If new materials or processes are applied, then device functionality is improved, but thickness measurement accuracy deteriorates due to physical property changes
Solution Approach 1:
The patent replaces spectroscopic ellipsometry (which relies on optical constants and mathematical functions) with X-ray reflectometry. This substitution eliminates the need to model complex material optical properties, as the fast-Fourier transform method directly extracts thickness from the spectral difference without requiring material-specific parameters.
Solution Approach 2:
The measurement approach changes from using optical constants and mathematical functions (ellipsometry) to using X-ray reflectivity spectra and fast-Fourier transform. This parameter change makes the measurement independent of material optical properties, allowing accurate thickness measurement of new materials without requiring updated mathematical models.
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 allows for more accurate thickness measurement of semiconductor devices by excluding structural and physical property influences, enabling precise determination of thin layer thickness without additional verification processes.
Implementation Method 1
measuring a first X-ray reflectivity from a substrate before formation of the object; forming the object on the substrate; measuring a second X-ray reflectivity from the substrate after the formation of the object
Implementation Method 2
transforming the calculated variation using a fast-Fourier transform; and determining a thickness of the object based on the transformed calculated variation
Data Source
AI summary
A method for analyzing an object includes measuring a first reflectivity of light from a surface and measuring a second reflectivity of light from the object, after the object is formed on the surface. A variation between the first and second reflectivities is calculated, and the variation is transformed by a predetermined transform. A thickness of the object is determined based on the transformed variation.