Investigation of surface contamination on silicon wafers with SIMS

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Abstract
Characterization of the surface of silicon wafers is necessary for control and development of cleaning procedures. An analytical approach for investigation of surface contaminants with SIMS is proposed. The major problem is the presence of the contaminants only in the native oxide (thickness ∼1.5 nm). This means that analysis has to be performed in a surface zone smaller than the implantation depth of the primary ions. Chemical matrix effects and a changing erosion rate are encountered owing to the native oxide and the dynamic process of primary ion implantation and sputtering. Owing to the necessity of analysing extremely thin surface layers very slow sputtering has to be applied (1–10 monolayers per min.). As a consequence the secondary ion intensities are low and hydrocarbon species interfere with the elements to be analysed. For the identification of the secondary ion signals the evaluation of isotopic ratios determined with low mass resolution (M/ΔM ∼ 350) is combined with measurement of high resolution mass spectra.