Ion-chromatographic assay of chromium(VI)-containing semiconductor etchants: Statistical comparison of two columns

Semiconductor etchants are concentrated-acid mixtures that are prepared under tight specifications. Assay procedures are needed to ensure that the proportion of each component is within a small percentage (usually 10 relative percent or less) of the target concentration. One such etchant class contains chromium trioxide, usually in combination with HF and HNO3. While several ion-chromatographic columns can be used to analyze most mineral acids, chromium(VI) presents a problem. This latter species is highly retained by many separators and may also degrade the resins. This paper compares two columns that showed potential for success with these assays: the AS11 and the AS16 separators (both from Dionex). These columns permit elution of chromium(VI) as chromate in 25 min or less. A representative mixture of HF, HNO3 and CrO3 was used in the research. Simultaneous calibration studies were conducted and the data sets analyzed statistically. Also investigated was the effect on the columns of repeated exposure to chromate.