The laser assisted atom probe has been proposed as a metrology tool for next generation semiconductor technologies requiring subnanometer depth resolution. In order to support its routine application, we carried out a quantitative assessment of the performance of the atom probe on semiconductor stacks. We analyzed a silicon, silicon-germanium multilayer-structure with atom-probe tomography (APT), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD). We demonstrate that APT outperforms SIMS by a factor of 3 in terms of depth-resolution providing a decay length of 0.2–0.6 nm/decade whereas the compositions and layer thicknesses are in close agreement with SIMS, HRXRD, and TEM.
Laser beam deflection in combination with optical heterodyne diffraction is used to detect surface acoustic waves that are generated by impulsive laser light on a Sn–CuxSny–Cu–Si multilayer structure with layer thicknesses of the order of 1 μm. The acoustic phase velocity dispersion curves of the lowest two-surface acoustic wave modes are determined by spectral analysis of the experimental signals. The sensitivity of the dispersive behavior to the thickness and elastic properties of the individual layers is analyzed on the basis of the experimental data and of simulated data with noise added. The elastic parameters of the CuxSny intermetallic alloy are determined. Statistical least squares and most squares uncertainties on all best fitting material parameters are determined, giving a quantitative measure of the feasibility of parameter extraction by this method. The feasibility of solving the inverse problem of elastic depth profiling of a multilayer by the proposed wideband and multimode SAW dispersion spectroscopy method is confirmed.
The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profile of heterogeneous functional gradient materials are investigated by comparing simulations of the surface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem is shown to be quite ill posed. The method is then applied to extract information on the depth structure of a glass-ceramic ͑ alumina͒ functionally graded material from experimental data. The surface acoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture of Al 2 O 3 and glass, with a sharp transition between the coating and the substrate. This is confirmed by scanning electron microscope with energy dispersive x-ray analysis.
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