Silicon Ion Detection in Alkaline Etchant via Fluoride Electrode
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Solution Overview
Problem
Conventional methods for detecting silicon, germanium, and titanium ions in alkaline etchant solutions lack the necessary sensitivity to accurately control etch rates and schedule etchant solution replacements in semiconductor processing, as they do not effectively react with these ions in alkaline environments.
Innovation Solution
A method utilizing a fluoride ion specific electrode (FISE) in an acidic test solution to measure the concentration of silicon, germanium, or titanium ions by adding a predetermined concentration of fluoride ions, which react with the ions to form undetectable hexafluorosilicic or hexafluorogermanic ions, allowing for precise calculation of their concentrations through a calibration curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods (NIR spectroscopy or ion chromatography) are used to detect silicon ions in alkaline etchant solutions, then the measurement process can be performed, but the sensitivity is insufficient to accurately control etch rates
Solution Approach 1:
The patent changes the chemical parameter (pH) of the etchant solution from alkaline to acidic by adding phosphoric acid. This parameter change enables the fluoride ions to react with silicon ions to form hexafluorosilicic acid, which can be detected by the fluoride ion selective electrode. The acidic environment is crucial for the reaction to proceed effectively, resolving the sensitivity issue in alkaline solutions.
Solution Approach 2:
The patent introduces fluoride ions as an intermediary substance that reacts with silicon ions to form a detectable complex (hexafluorosilicic acid). This intermediary mechanism transforms the undetectable silicon ion concentration into a measurable fluoride ion depletion signal, achieving sensitive detection without directly measuring silicon ions.
2Measurement precision
If fluoride ions are added to alkaline etchant solutions to react with silicon ions, then silicon concentration can be measured, but fluoride does not react with silicon ions in alkaline solutions
Solution Approach 1:
The patent fundamentally changes the pH parameter from alkaline to acidic to enable the fluoride-silicon reaction. In the acidic environment created by phosphoric acid, fluoride ions become reactive toward silicon ions, forming hexafluorosilicic acid. This parameter change restores the chemical reactivity needed for measurement.
3Productivity
If etchant solution replacement is based on a schedule rather than actual need, then replacement timing is standardized, but productivity is reduced due to unnecessary replacements
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the silicon ion concentration in the etchant solution through fluoride ion selective electrode measurements. This real-time concentration data provides feedback on etchant depletion, enabling dynamic adjustment of replacement timing based on actual solution condition rather than fixed schedules, thereby optimizing productivity.
4Measurement precision
If high sensitivity detection methods are developed for silicon, germanium, and titanium ions, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent uses fluoride ions as a simple intermediary that reacts with silicon, germanium, or titanium ions to form detectable complexes. This approach maintains system simplicity by using readily available reagents and standard fluoride selective electrodes, avoiding the need for complex specialized detection equipment while achieving high measurement precision.
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
Enables accurate, rapid, and cost-effective determination of etchant product concentrations, allowing for optimized etch times and solution replacements, thereby improving the quality and yield of semiconductor devices and reducing waste and costs.
Implementation Method 1
In the acidic test solution, silicon exists primarily as the protonated HSiO3− and H2SiO3 species, which react with fluoride ions to form the hexafluorosilicic ion (SiF62−), which is not detected by the FISE.
Data Source
AI summary
Silicon ions in an alkaline etchant solution are analyzed by acidifying a sample of the etchant solution, adding fluoride ions in excess of the concentration required to react with all of the silicon ions, and using a fluoride ion specific electrode (FISE) to detect free fluoride ions in the resulting test solution. Good sensitivity and precision are provided by using a relatively acidic test solution and only a slight excess of fluoride ions, and limiting the analysis range to the maximum expected silicon concentration in the etchant solution.