Aluminum and its alloys are used for wiring in microchips [1]. To selectively wet etch aluminum, an etching bath made of phosphoric acid, nitric acid, and acetic acid (PAN etchant) is used. This acid mixture must be analyzed and monitored for optimal and efficient etching.

The SEMI C37 standard uses potentiometric titration to measure total acidity and phosphoric acid content. However, nitric acid must be analyzed by UV/VIS spectroscopy, while acetic acid content is calculated from the other results [2]. Thermometric titration (TET) is an alternative PAN etchant analysis method which can determine all three acids quickly.

In this Application Note, the acid concentrations are determined in sequence using a single titration. Compared to potentiometric titration, TET is faster and more convenient. On a fully automated system, the complete analysis takes about 95 seconds.