Determination of sub-2-nm SiO2 interlayer thickness using secondary ion mass spectrometry

The development of secondary ion mass spectrometry (SIMS) methodology for t he determination of sub-2-nm SiO2 interlayer thickness is reported here. Th e SiO2 interlayer to be evaluated is within the structure of polycrystallin e Si-SiO2-Si substrate. The polycrystalline Si layer can be up to a few hun dred nanometers thick. The sample is analyzed by SIMS and a concentration-d epth profile of oxygen is acquired. High-energy Csf primary ion bombardment is used, so that the thin SiO2 layer is diluted by ion beam mixing. A 14.5 keV net impact energy provides sufficient mixing to change the composition of the interface from that of stoichiometric SiO2 to Si with a high dose o f oxygen. The areal density of the interfacial oxygen peak is calibrated ag ainst a SIMS oxygen ion implant standard with a precision of better than 3% . The SiO2 thickness then is calculated with equal precision using the form ula derived. In the present work, the differentiation among interfacial oxi de thicknesses of 5-10 Angstrom with a step width of 1 Angstrom is demonstr ated by this SIMS method with good precision and accuracy. Copyright (C) 20 01 John Wiley & Sons, Ltd.