Online process control of acidic texturisation baths with ion chromatography

Etching of silicon with mixtures of hydrofluoric acid and nitric acid is a widely used process in silicon solar cell fabrication. One precondition for an optimized usage of the acidic etching baths is the exact knowledge of the chemical bath composition. In this paper, we investigated a fast and online-capable method for the total analysis of all bath constituents by ion chromatography. The chromatographical system consists of a low-volume injection valve, which injects the concentrated samples directly into the KOH-based eluent. After separation and detection of nitrate and fluoride, a post-column derivatization with sodium molybdate is applied to detect the hexafluorosilicic acid, which enriches in the texturisation bath during the etching process. The results of the presented approach are discussed and compared with already published chromatographical and titration methods found in literature.