In the 'graded-etching' method for SiO2/Si, the thickness Of SiO2 decreases almost linearly. We have applied graded-etching method to TOF-SIMS to get information on the secondary ion emission from different thickness Of SiO2 systematically. The intensities of Si-containing ions changed at thickness of less than about 2 urn on these samples. The changes of sensitivities for metals also occurred at this region. The information depth of TOF-SIMS in this system are supposed to be less than about 2 nm. (C) 2002 Elsevier Science B.V. All rights reserved.