Determination of acetic, phosphoric, and nitric acid mixtures

Importance of the Topic

Accurate determination of phosphoric, nitric and acetic acid concentrations in aluminum etching solutions is critical for process control in semiconductor fabrication. Quality monitoring of these acid mixtures ensures consistent etch rates, reduces defects, enhances yield and supports environmental and safety compliance.

Objective and Study Overview

This application note describes a thermometric titration method to quantify mixtures of phosphoric, nitric and acetic acid used in aluminum etching. The study aims to establish a fast, reliable analytical procedure suitable for routine quality assurance in semiconductor manufacturing.

Methodology and Instrumentation

Samples are prepared by weighing a defined aliquot of the acid mixture into a volumetric flask containing saturated NaCl solution and diluting to volume. Titration with 2 mol/L NaOH is performed at a constant dosing rate to generate three exothermic endpoints corresponding to the dissociation of nitric acid, acetic acid, and the three dissociation stages of phosphoric acid. Endpoint volumes are blank-corrected using regression analysis on a series of low-mass samples. Composition is calculated by applying the corrected endpoint differences, titrant concentration and molecular weights.

Used Instrumentation

• 814 USB Sample Processor
• 859 Titrotherm thermometric titrator
• Thermoprobe temperature sensor
• 24×75 mL sample rack and 75 mL beakers
• 802 rod stirrer with 104 mm propeller
• 800 Dosino with 10 mL dosing unit
• tiamo software for data evaluation

Main Results and Discussion

Blank determinations enabled systematic error correction of each endpoint. The method delivered average compositions of 61.6 % H3PO4, 4.1 % HNO3 and 21.4 % CH3COOH with standard deviations of 0.3 %, 0.2 % and 0.3 %, respectively. Thermometric titration plots based on the second derivative of temperature accurately identified all three endpoints, demonstrating high precision and linear endpoint shifts over a range of sample masses.

Benefits and Practical Application

• High precision and reproducibility in complex acid mixtures
• Rapid analysis suitable for routine quality control
• Minimal sample pretreatment with simple dilution and salt addition
• Automated blank correction improves accuracy
• Applicable to industrial semiconductor etching processes

Future Trends and Potential Applications

Emerging trends include inline and real-time titration sensors for continuous process monitoring, integration with chemometric data analysis, further miniaturization of thermometric sensors, and expansion to other industrial acid mixtures. Adoption of greener titrants and automation enhancements will drive future developments.

Conclusion

The described thermometric titration method provides a fast, accurate and reproducible approach for determining phosphoric, nitric and acetic acid ratios in aluminum etching solutions, supporting robust process control in semiconductor manufacturing.