Analysis of Si wafer coated by spin-on-glass for laser ablation ICP-MS

A method involving laser ablation sector type inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed for the direct determination of metal impurities in the spin-on-glass (SOG) layer on a silicon wafer surface. For a reference wafer, the preparation procedure for the SOG layer was re-designed and optimized in a sequence of spiking of known amounts of metal contaminants in SOG chemical (Model: P-MSQ, 5.5% silicon dioxide in polypylene and glycol-dimethyl ether), spin-coating, and baking. Optimization of the procedure affected the contamination levels of metals which were determined by a solution scanning sampling followed by a sector type ICP-MS analysis. For homogeneity study, 74 sectors of the SOG layer were individually scanned using a laboratory-made automatic scanner with a scanning solution. The average contamination levels of each sector were obtained in the range of 10 ¹⁰-10¹² atoms cm^-2 under optimized conditions. SEM images of craters for LA, each produced by one laser shot (266 nm, 9 mJ per pulse), showed that the depths of the craters were larger than the thickness of the SOG layer, 2350 , and the diameter increased with the power and decreased with de-focused beam diameter. Limits of detection of LA-ICP-MS were estimated at ∼10⁹ atoms cm^-2 on the Si wafer surface, depending on the element.