Acids, Bases, and Etching Agents

Concentrated acids also play an important role in the manufacturing of semiconductor devices. Hydrofluoric acid, for example, is used to remove oxide layers from wafer surfaces [139]. Glycolic acid is a major component of non-aqueous soldering agents [140] and concentrated orthophosphoric acid is used for etching silicon nitride on wafer surfaces [141]. 

The extremely large excess of matrix ions renders the analysis of anionic impurities very difficult. Concentration differences between matrix and analyte ions of 10 1 are not unusual. (Example chloride contamination in the range of 100 pg/L in 24.5% (v/v) HF) Although the matrix problem can be solved by diluting the acids, the sample then falls below the detection limits for the analyte ions. Siriraks et al. [142], for example, obtained detection limits between 0.04 and 0.08 mg/L for chloride, bromide, orthophosphate, and sulfate in 0.25 % HF by direct injection. Utilizing an alternative matrix elimination technique — methanol/water rinse of the concentrator column after pre-concentration of HF — the tolerable HF concentration could be increased to 5 %, while maintaining the detection limit. However, 

2 mL concentrator column lonPac CG12A solute concentrations 5 pg/L each of lithium (1), sodium (2), ammonium (3), potassium (4), magnesium (6), and calcium (7), 140 pg/L rubidium (5) as an internal standard (taken from [138]). 

For the determination of cationic impurities in concentrated acids, the Au-toNeutrahzation technique must be used this technique was outlined above in Section 9.2. The direct injechon of the acids is not possible for lack of sensitivity. Moreover, if a weak acid cation exchanger was used for the simultaneous analysis of mono- and di-valent cations, the high acid concentration would lead to a 

55 mL/min concentrator column lonPac AG9-HC (4-mm) separator column lonPac 

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