Use of spin-coated TXRF reference samples for ToF-SIMS metal contaminant quantification on silicon wafers

Abstract

Among the emerging techniques able to reveal the metals contaminating the wafer surface in the manufacturing processes of microelectronic devices, time-of-flight secondary ion mass spectrometry (ToF-SIMS) is considered very promising. Despite the potentialities of this analytical tool, some of the phenomena that affect the signal intensity are not fully investigated and still hinder the use of the technique. To evaluate the capabilities of ToF-SIMS to detect quantitatively metal traces on silicon wafers, we analyzed contaminated reference samples produced by spin coating. These standards were also characterized by total reflection x-ray fluorescence spectroscopy (TXRF), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The comparison between results obtained by TXRF and ToF-SIMS allowed us to evaluate the metal detection sensitivities and to estimate the detection limits for most of the elements that produce detrimental effects on device yield. We prove that the metals' secondary ion yields are governed by silicon oxide matrix effects and that a linear relationship between the ToF-SIMS signal intensity and the elemental areal density holds for most of the considered elements for changes in the uppermost layer composition ranging over more than three orders of magnitude. Besides, it is shown that although spin-coating is commonly employed to produce reference samples, the lateral distribution and the physical status of the contaminants produced by this technique may seriously affect the results obtained by both ToF-SIMS and TXRF.