XRF Measurement Accuracy via Relative Emission Factor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing X-ray microfluorescence methods struggle to accurately measure properties of small features on semiconductor wafers due to X-ray beam spill-off onto surrounding areas, leading to inaccurate fluorescence intensity measurements.
Innovation Solution
A method and apparatus that involve scanning an X-ray beam across a calibration sample to compute a relative emission factor, which is then applied to measurements on a test sample to correct for background contributions, allowing for accurate determination of feature properties like composition and thickness, even when the beam profile changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If X-ray beam is focused to small diameter to measure small features, then measurement precision is improved, but beam spill-off onto surrounding areas increases causing inaccurate fluorescence intensity measurements
Solution Approach 1:
The patent applies preliminary action by performing a calibration scan before the actual measurement to determine the beam profile and calculate correction factors. The calibration phase maps the beam intensity distribution across the feature and surrounding areas, storing this information for later use in correcting measurement data. This preliminary characterization of the beam allows the system to compensate for spill-off effects during subsequent measurements.
Solution Approach 2:
The patent implements feedback by using the measured beam profile from calibration to calculate correction factors that are then applied to the actual measurement data. The system measures the beam intensity distribution, computes correction factors based on the ratio of feature-to-background emissions, and uses these factors to correct the fluorescence intensity measurements, thereby compensating for the harmful spill-off effect.
2Measurement precision
If calibration is performed for each beam profile change to maintain accuracy, then measurement precision is improved, but productivity decreases due to repeated calibration requirements
Solution Approach 1:
The system performs preliminary calibration to establish the beam profile and correction factors, storing this calibration data for reuse. When the beam profile changes, the system can determine whether recalibration is necessary by comparing new beam characteristics against stored calibration data, allowing calibration to be performed only when truly necessary rather than with every beam profile change.
Solution Approach 2:
The patent applies parameter changes by monitoring beam profile parameters and using these parameters to determine when recalibration is needed. The system measures key beam parameters during operation and compares them against calibration thresholds, allowing flexible adaptation to beam profile changes while avoiding unnecessary recalibrations that would reduce productivity.
3Measurement precision
If X-ray beam is directed at small features, then measurement precision is improved, but background emissions from surrounding areas contaminate the signal
Solution Approach 1:
The patent extracts the harmful background emission component from the total measured signal by performing separate measurements or calculations of the feature emission and background emission. The calibration scan allows the system to separately characterize the background emission from surrounding areas, which is then subtracted or otherwise removed from the total measurement to isolate the pure feature signal.
Solution Approach 2:
The patent uses correction factors as an intermediary element that mediates between the contaminated measurement signal and the true feature properties. These correction factors, derived from calibration data, serve as a mathematical intermediary that when applied to the raw measurement data, eliminate the background emission contamination and reveal the accurate feature characteristics.
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 accurate and flexible measurement of small features by compensating for background emissions, maintaining measurement accuracy without the need for repeated calibration, even when the X-ray beam profile changes.
Implementation Method 1
X-ray fluorescence (XRF) measurement, and specifically X-ray microfluorescence (i.e., X-ray fluorescence using focused excitation beams of small diameter, typically less than 100 μm), is commonly used in testing semiconductor wafers
Data Source
AI summary
A method for X-ray measurement includes, in a calibration phase, scanning a first X-ray beam, having a first beam profile, across a feature of interest on a calibration sample and measuring first X-ray fluorescence (XRF) emitted from the feature and from background areas of the calibration sample surrounding the feature. Responsively to the first XRF and the first beam profile, a relative emission factor is computed. In a test phase, a second X-ray beam, having a second beam profile, different from the first beam profile, is directed to impinge on the feature of interest on a test sample and second XRF emitted from the test sample is measured in response to the second X-ray beam. A property of the feature of interest on the test sample is computed by applying the relative emission factor together with the second beam profile to the measured second XRF.