Organic Layer Reduces Silicon Fluorescence in TXRF Analysis
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Solution Overview
Problem
Total reflection x-ray fluorescence spectrometry (TXRF) is hindered by strong fluorescence emission from silicon substrates, which masks the detection of analytes due to the strong fluorescence emission signal, requiring pretreatment techniques like vapor phase decomposition and resulting in loss of areal distribution information.
Innovation Solution
A process involving a workpiece with a substrate and an overlying organic layer, such as resist material, is used to reduce substrate fluorescence, allowing detection of analytes with lower atomic numbers and improving detection limits by using XRF or TXRF spectroscopy, where the organic layer is sufficiently thick to prevent substrate excitation during analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If TXRF is used to analyze analytes on silicon substrate, then the analysis can be performed without pretreatment, but the strong fluorescence emission from silicon masks the analyte signal
Solution Approach 1:
A carbon-based layer (such as polyimide or resist material) is deposited over the silicon substrate to act as an intermediary that blocks the strong silicon fluorescence signal from reaching the detector, while still allowing the analyte signal to be detected. This mediator layer enables the silicon substrate to be used without pretreatment while resolving the fluorescence masking problem.
Solution Approach 2:
The harmful silicon fluorescence signal is extracted or removed from the detection path by placing a carbon-based layer between the silicon substrate and the X-ray detector. This layer absorbs or blocks the silicon fluorescence photons, effectively removing this interfering signal from the measurement while preserving analyte detection capability.
2Difficulty of detecting and measuring
If vapor phase decomposition pretreatment is applied to remove silicon fluorescence, then the analyte detection is enabled, but the areal distribution information is lost and additional time and expense are required
Solution Approach 1:
The carbon-based layer serves as a protective intermediary that allows the silicon substrate to be analyzed in its original state without requiring vapor phase decomposition. This preserves the areal distribution information of the analyte while blocking the harmful silicon fluorescence signal, eliminating the need for information-loss-inducing pretreatment.
Solution Approach 2:
The carbon-based layer is deposited in advance over the silicon substrate before analyte deposition, creating a protective barrier that prevents silicon fluorescence from interfering with subsequent analyte detection. This preliminary action eliminates the need for post-deposition pretreatment and preserves all areal distribution information.
3Object-generated harmful factors
If the organic layer is made sufficiently thick to prevent substrate excitation, then the substrate fluorescence is reduced, but the analyte detection sensitivity may be affected
Solution Approach 1:
The thickness of the carbon-based layer is optimized to a specific range (typically 1-10 micrometers) that is sufficient to block silicon fluorescence photons while remaining thin enough to allow analyte X-ray signals to pass through with acceptable intensity. This parameter optimization balances the two competing requirements.
Solution Approach 2:
The carbon-based layer is applied uniformly across the substrate surface, providing consistent fluorescence blocking throughout the analysis area. The layer's material properties (carbon composition) are specifically chosen to provide optimal attenuation of silicon fluorescence while maintaining transparency to analyte signals.
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 enables detection of analytes at lower concentrations, including elements with atomic numbers as low as 11, reduces the fluorescence emission from silicon, and retains areal information, allowing for more sensitive and accurate analysis without the need for pretreatment, achieving detection limits as low as 1E9 atoms/cm2.
Implementation Method 1
In total reflection x-ray fluorescence spectrometry ('TXRF'), the primary x-ray beam strikes a silicon substrate at a very low angle (less than 1°), almost parallel to the surface. At this very low or 'grazing' angle, a phenomena termed 'total reflection' occurs and the x-ray beam, which would normally penetrate through the entire silicon substrate if the primary x-ray beam would strike the silicon substrate perpendicular to the surface, reflects off the surface
Implementation Method 2
analyte atoms on a surface of a silicon substrate absorb the energy of the primary x-ray photon and undergo the process of fluorescence, which results in the emission of a secondary fluorescent x-ray at an energy that is characteristic of the analyte atom
Data Source
AI summary
A workpiece, including a substrate and overlying layer, can be exposed to a region, such as a process chamber, to test for the presence of an analyte. Detected fluorescence emission signals during TXRD due to the substrate are significantly reduced, allowing the analyte to be detected at lower concentrations. In one embodiment, the substrate can principally include silicon, and the layer can include an organic layer (e.g., resist, polyimide, etc.) The organic layer allows analytes with an atomic number as low as 11 to be detected. Also, the detection limits for nearly all analytes can be reduced because the detector is not receiving a disproportionately larger number of fluorescence emission from silicon. In additional, areal information regarding the analyte with respect to position over the substrate can be obtained. Detection levels as low as 1E9 atoms/cm2 are possible.