Fragmentation of molecular compounds on silicon wafers and low dielectric constant materials studied by time-of-flight secondary ion mass spectrometry using a polyatomic ion source

Abstract

Recent time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies using primary cluster ion sources such as Aun+, SF n+, Bin+ or C60+ have shown polyatomic ions to be more appropriate for the detection of high mass molecular secondary ions than monoatomic ion sources like Ga+, thanks to secondary ion yield and ion formation efficiency enhancements. This work is part of a study aiming at improving molecular compound quantification at the surface of microelectronics industry substrates by taking advantage of a polyatomic ion source in ToF-SIMS analysis. It focuses on the case of a phthalate-related contamination. Fundamental parameters like secondary ion yield, damage cross section and secondary ion efficiency were studied as a function of the size and the energy of the primary ions. The substrate composition influence on the ToF-SIMS results was also studied by comparing several substrates of interest in the microelectronics industry such as silicon wafers and low dielectric constant materials SiOxCyHz. Phthalate-related secondary ions detected at the surface of the contaminated surfaces were compared and a fragmentation pathway of the di-isononyl phthalate (DNP) molecule was determined. A drastic improvement of the secondary ion yield was provided when using a polyatomic ion source. Furthermore, a clear increase in damage cross section was observed as a function of the secondary ion size for a given Bin primary ion as well as an increase for a given fragment as a function of the number of Bi atoms in the Bin aggregate. This led to a lower static limit when taking into account higher phthalate fragments and primary ions of larger size. Copyright © 2008 John Wiley & Sons, Ltd.