Determination of organic contaminations on Si wafer surfaces by static ToF-SIMS: Improvement of the detection limit with C60 + primary ions

This study deals with the secondary ion yield improvement induced by using C60 + primary ions instead of Ga+ to enhance the detection thresholds of the organic contaminations at the Si wafer surfaces by ToF-SIMS. For that purpose, a piece of Si wafer has been analysed with both ion sources. A large improvement is observed for the detection of hydrocarbon contaminants with C60 + primary ions as compared to Ga+ ions. A similar improvement for organic contaminations, such as phthalates and aliphatic amines, is observed in both secondary ion polarities. The Si atomic ion constitutes a minor peak with C60 + ions while it dominates the spectrum in the case of Ga+ ions. However, with the C60 + source, inorganic combination peaks with the elements Si and O, are observed in the positive spectra (i.e. Si2O2H+), while they are marginal with the Ga+ source. Furthermore, a series of negative silicon oxide clusters, SinO(2n+1)H , is observed up to n = 16 (977m/z) in the case of C60 + ions.With Ga+ ions, the largest negative silicon oxide cluster corresponds to n = 4 (257m/z). The detection of backscattered C60 fragments is evoked to explain the origin of some hydrocarbon peaks with low H content. On average, for a comparable number of primary ions per spectrum, the C60 + ion source gives intensities between two and four orders of magnitude higher than the Ga+ one