Evaluation of time-of-flight secondary ion mass spectrometry for metal contamination monitoring on Si wafer surfaces

Due to stringent IC-production requirements, the metallic contamination of silicon surfaces decreases to very low concentration levels (below 10(10) atom/cm(2)). Therefore new alternatives to measure the presence of these contaminants and to quantify their amounts are investigated. This study focuses on the capabilities of time of flight secondary ion mass spectrometry (TOF-SIMS). It compares and combines TOF-SIMS results with those of the standard technique direct total reflectance X-ray fluorescence spectroscopy (TXRF). Next, it investigates the influence of the surface oxidation state (i.e., bare silicon, native and thermal oxide) on the TOF-SIMS signal response. Then, TOF-SIMS surface spectra are quantified using relative sensitivity factors, according to two different approaches (experimentally vs, theoretically derived). Finally, the influence of oxidation ambient on Fe redistribution in the thermal oxide layer is studied using the TOF-SIMS dual beam option to perform depth profiling. A good general agreement is obtained between the quantified TOF-SIMS surface spectra and the TXRF values. For the Fe distribution in the oxide layer, TOF-SIMS reaches qualitatively the same conclusions as vapor-phase decomposition-droplet collection TXRF For 5 nm oxide samples no difference between both furnace ambients can be observed. For 15 nm oxides, however, more Fe is trapped in the oxide when oxygen is added to the ambient. (C) 2000 The Electrochemical Society. S0013-4651(99)06-067-X.All rights reserved.