BHF Solution Concentration Measurement Using pH and Glass Electrode
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Solution Overview
Problem
Conventional optical measurement devices struggle to accurately measure low concentrations of hydrofluoric acid (HF) in buffered hydrofluoric acid (BHF) solutions used in semiconductor manufacturing, due to reduced sensitivity in low concentration regions.
Innovation Solution
A BHF solution concentration measurement device that utilizes a pH meter and a relationship storage unit to calculate HF concentration based on pH values, leveraging the sensitivity of pH to HF concentration while being insensitive to NH4F concentration, with a glass electrode pH meter that minimizes solution usage and avoids convection effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical measurement devices are used to measure HF concentration in low concentration BHF solutions, then the measurement structure remains simple, but the measurement precision deteriorates due to reduced sensitivity in low concentration regions
Solution Approach 1:
The invention changes the measurement parameter from direct optical detection of HF concentration to pH value measurement. By measuring pH (which reflects H+ ion concentration) and using the established relationship between pH and HF concentration in BHF solutions, the system achieves high measurement precision in low concentration regions where optical methods fail. The pH meter detects hydrogen ion activity, which remains sensitive even when HF concentration is diluted to one tenth or one hundredth of conventional levels.
2Measurement precision
If a glass electrode pH meter is used to measure pH in BHF solution, then the responsiveness to HF concentration improves, but the glass electrode is damaged by corrosion from the BHF solution
Solution Approach 1:
The invention introduces a protective intermediary structure - a tube formed from response glass that serves as both the measurement window and protective barrier. This tube allows the glass electrode to measure pH through its wall while being protected from direct contact and corrosion by the BHF solution. The tube acts as a mediator that transmits the measurement function while isolating the electrode from the corrosive environment, enabling reliable continuous measurement.
3Quantity of substance
If a narrow diameter tube is used for the pH meter response glass, then the quantity of BHF solution required for sampling is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The invention applies partial action by using a narrow diameter tube that requires only a small quantity of BHF solution for effective measurement. The tube diameter is optimized to provide sufficient measurement accuracy while minimizing solution volume requirements. This partial approach (narrow but not extremely narrow) achieves the benefit of reduced solution consumption without requiring excessively tight manufacturing tolerances that would be needed for ultra-fine capillaries.
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 precise measurement of HF concentration in low concentration regions with reduced solution usage and improved accuracy, allowing real-time monitoring of HF levels during semiconductor etching processes.
Implementation Method 1
a pH meter that measures the pH of the BHF solution
Data Source
AI summary
In order to make it possible to accurately measure the HF concentration in a BHF solution in a low concentration region using a simple structure, there are provided a relationship storage unit that stores relationships between a pH of a BHF solution and an HF concentration, a pH meter that measures the pH of the BHF solution, and a concentration calculation unit that refers to relationships stored in the relationship storage unit, and calculates the HF concentration from the pH values measured by the pH meter.