X-ray Fluorescence Inspection Small Features
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Solution Overview
Problem
In X-ray-based analysis of fine features on semiconductor wafers, precise alignment of the X-ray beam with the feature of interest is time-consuming and often imperfect, especially when the feature is smaller than the excitation beam, leading to mixed signals with background emission, particularly in high-energy applications where narrow X-ray sources and optics are lacking.
Innovation Solution
The method involves irradiating a sample with an X-ray beam having a central spot and a surrounding halo, measuring X-ray emission at multiple positions, and comparing these measurements to determine the feature's properties, such as concentration or thickness, by adjusting for the overlap between the beam and the feature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow X-ray beam is used to achieve high spatial resolution for small features, then measurement precision improves, but device complexity increases due to the need for specialized optics and precise alignment mechanisms
Solution Approach 1:
The patent segments the X-ray beam into a central spot and a surrounding halo, allowing differential measurement approaches. The central spot provides high-resolution signal from the feature while the halo provides background reference, enabling resolution without requiring perfectly narrow beams
Solution Approach 2:
The patent introduces an intermediary measurement approach by using the halo region as a mediator to characterize background emission. This allows the system to work with broader beams while still achieving accurate feature characterization through comparative measurement between central and halo regions
2Measurement precision
If precise alignment of the X-ray beam with the feature is performed, then measurement accuracy improves, but productivity decreases due to excessive time consumption
Solution Approach 1:
The patent performs preliminary characterization of the beam profile (central spot and halo) before actual measurement. This pre-characterization allows the system to work with broader beams and less precise alignment during production measurements, as the beam structure is already understood and compensated for in the analysis
Solution Approach 2:
The measurement method is self-aligning in that it does not require perfect beam-feature alignment. By measuring at multiple positions and using the halo as reference, the system automatically compensates for misalignment, eliminating the need for time-consuming manual alignment procedures
3Ease of operation
If the X-ray beam is broader to cover larger features, then ease of operation improves, but measurement precision deteriorates due to mixed signals from background emission
Solution Approach 1:
The patent segments the beam and measurement into central spot and halo components. The central spot measures feature signal while the halo measures background, allowing broader beams to be used without sacrificing precision because the background contribution is separately characterized and subtracted
Solution Approach 2:
The patent extracts the background emission component by measuring the halo region separately. This extracted background information is then used to clean the central measurement, allowing broader beams to be used while maintaining signal purity through mathematical separation of feature and background contributions
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 characterization of small features by isolating the signal from the background emission, improving the precision and efficiency of X-ray fluorescence measurements, even when beam alignment is imperfect.
Implementation Method 1
X-ray fluorescence (XRF) measurement... is a well-known technique for determining the elemental composition of a sample. XRF analyzers generally include an X-ray source, which irradiates the sample, and an X-ray detector, for detecting the X-ray fluorescence emitted by the sample in response to the irradiation.
Data Source
AI summary
A method for inspection includes irradiating a sample using an X-ray beam, which is focused so as to define a spot on a surface of the sample. At least one of the sample and the X-ray beam is shifted so as to scan the spot along a scan path that crosses a feature on the surface. Respective intensities of X-ray fluorescence emitted from the sample responsively to the X-ray beam are measured at a plurality of locations along the scan path, at which the spot has different, respective degrees of overlap with the feature. The intensities measured at the plurality of the locations are processed in order to compute an adjusted value of the emitted X-ray fluorescence over the scan path. A thickness of the feature is estimated based on the adjusted value.