Quantitative static Time-of-Flight Secondary Ion Mass Spectrometry analysis of anionic minority species in microelectronic substrates

Abstract

Reliability and yield of nano-electronic devices can be seriously affected by the presence of surface contamination, even at low concentration. The microelectronics industry is, thus, in need for a quantitative, highly sensitive surface analysis technique capable of detecting both elementary and molecular species present at the surface. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) provides a submicronic lateral resolution and excellent sensitivity with high secondary ion yields on a broad mass range but, nevertheless, remains a qualitative technique. To convert normalized ion intensities into concentrations and, thus, to provide reliable quantification, the so-called relative sensitivity factors (RSFs) need to be determined. In earlier studies, ToF-SIMS RSFs for trace metals were determined from the calibration of ToF-SIMS positive ion intensities against quantitative analysis techniques able to determine a surface coverage such as vapour phase decomposition inductively coupled plasma mass spectrometry (VPD-ICP-MS) or total reflection X-ray fluorescence (TXRF) results. Here, the aim is to quantify elementary anionic minority species (S, Cl, P, Br). Deliberately contaminated samples were prepared and analyzed with ToF-SIMS and several quantitative surface analytical techniques like TXRF, liquid phase extraction ionic chromatography (LPE-IC) or VPD-ICP-MS. None of these latter techniques can by itself successfully handle all the anionic species cases and ToF-SIMS turns out to be the more versatile and precise characterization technique in this context.