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

Abstract

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 10¹⁰–10¹² 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 Å, 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.