Dropping mode chemiluminescence system with a poly(dimethylsiloxane) cell for applications to semiconductor processes.

A lab-made chemiluminescence system with a polymer cell for the dropping mode was used to determine ultra-trace metal ions in hydrofluoric acid (HF) and the standard cleaning solution-1 (SC-1) used in semiconductor manufacturing processes. The cell was made of poly(dimethylsiloxane) (PDMS) with dimensions of about 10 mm i.d. and 8 mm in height, was cheap, disposable, chemically inert to alkalis and acids, especially HF, and was optically transparent in the visible region. A dropping method for sample injection was adopted to minimize pulsation and the dramatic pH change of the luminol-H2O2 reagent when adding the sample. The average sample weight of a single drop was 7.17 microg with a remarkable reproducibility of +/-0.37% relative standard deviation (RSD). This very small sample volume compared to the reagent volume made it possible to avoid any precipitation being formed when HF was added. For an application, Fe was determined in deionized (d.i.) water, sulfuric acid, SC-1, and a diluted HF (1:200 DHF) solution, which have been commonly used in semiconductor manufacturing processes. The limits of detections for Fe2+ in those solutions were found to be in the range of 42 to 62 pg ml(-1). Based on the analytical results, this chemiluminescence system with the PDMS cell was reproducible, resistant to HF, had less sample consumption and waste generation, and was sensitive enough to apply to the semiconductor industry as an on-line monitoring sensor. Although this chemiluminescence system does not have selectivity for each specific metal ion, it can be used as an on-line sensor to monitor the metal contamination level of Fe, Cu, Co, etc., which are major elements of concern in the semiconductor manufacturing process.