Monitoring metal ion contamination onset in hydrofluoric acid using silicon-diamond and dual silicon sensing electrode assembly

Potentiometric detection of trace levels of metallic contamination onset in hydrofluoric acid using a silicon-based sensor in conjunction with two non -contaminating reference electrode systems is presented in this paper. In t he first case, conductive diamond was used as a non-contaminating reference electrode. Cyclic voltammetry and open-circuit potential experiments demon strated the feasibility of using a conductive diamond film electrode as a q uasi-reference electrode in the HF solution. In the second case, a dual sil icon electrode system was used with one of the silicon-based electrodes pro tected with an anion permeable membrane behaving as the quasi-reference ele ctrode. The dual silicon sensing electrode system possessed an additional o perational advantage of being unaffected by the solution acidity. Though bo th sensing configurations were able to detect the metal ion contamination o nsets at the parts-per-trillion to parts-per-billion levels, the dual silic on electrode design showed a greater compatibility for the on-line detectio n of metallic impurities in HF etching baths commonly used in semiconductor processing.