Chapter 8 - Surface Analysis Methods for Contaminant Identification

Abstract

When selecting a method for surface contaminant analysis one must consider factors such as the size, shape, morphology, composition, volatility, concentration, and history of both the substrate and the contaminant. In addition, one must decide whether the study should provide qualitative or quantitative results and what specific type of information is required. Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and low-energy ion scattering (LEIS) are four classical surface analysis methods, each capable of quantitative analysis of sub-monolayer contaminants. These methods differ significantly in applicability for particle analysis. LEIS and XPS require particles of 100 and 10mm diameters, respectively. In contrast, sub-micrometer particle analysis requires the use of TOF-SIMS or AES with AES, having the smallest analysis size of 10nm diameter. Whenever elemental analysis is insufficient for contaminant identification, XPS and TOF-SIMS are the methods of choice. This is particularly true for analysis of organic materials. Often the choice between XPS and TOF-SIMS can be made based on whether the contaminant is a complete unknown for which XPS excels or whether a specific contaminant needs to be identified for which TOF-SIMS excels. Minimum detection-limit is often a deciding factor in method selection. LEIS and AES generally have limited sensitivity with XPS being only slightly more sensitive.