Depth resolution at organic interfaces sputtered by argon gas cluster ions: the effect of energy, angle and cluster size

An analysis is presented of the effect of experimental parameters such as energy, angle and cluster size on the depth resolution in depth profiling organic materials using Ar gas cluster ions. The first results are presented of the incident ion angle dependence of the depth resolution, obtained at the Irganox 1010 to silicon interface, from profiles by X-ray photoelectron spectrometry (XPS). By analysis of all relevant published depth profile data, it is shown that such data, from delta layers in secondary ion mass spectrometry (SIMS), correlate with the XPS data from interfaces if it is assumed that the monolayers of the Irganox 1010 adjacent to the wafer substrate surface have an enhanced sputtering rate. SIMS data confirm this enhancement. These results show that the traditional relation for the depth resolution, FWHM = 2.1Y(1/3) or slightly better, FWHM = PXY1/3/n(0.2), where n is the argon gas cluster size, and P-X is a parameter for each material are valid both at the 45 degrees incidence angle of the argon gas cluster sputtering ions used in most studies and at all angles from 0 degrees to 80 degrees. This implies that, for optimal depth profile resolution, 0 degrees or >75 degrees incidence may be significantly better than the 45 degrees traditionally used, especially for the low energy per atom settings required for the best resolved profiles in organic materials. A detailed analysis, however, shows that the FWHM requires a constant contribution added in quadrature to the above such that there are minimal improvements at 0 degrees or greater than 75 degrees. A critical test at 75 degrees confirms the presence of this constant contribution.