| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS-WeA |
| Session: | Angle-resolved X-ray Photoelectron Spectroscopy |
| Presenter: | C. Brundle, C. R. Brundle and Associates |
| Authors: | C. Brundle, C. R. Brundle and Associates G. Conti, Applied Materials |
| Correspondent: | Click to Email |
ARXPS can be used in two ways to obtain depth distribution information for the near surface region of materials. The first is the Relative Depth Profiling (RDP) approach, which is completely qualitative and provides a "layer ordering" under certain conditions (the material has to be genuinely approximatable by a layer structure and a given XPS resolvable species should not be present in more than one layer). Provided there is sufficient signal intensity to be observed at two angles, the method is usable, which often means qualitative information beyond 100Å depth can be obtained. The second approach is to model the data based on inelastic mean free path lengths, the Beer-Lambert law, and some degree of entropy contribution (such as the Max Entropy approach), in an attempt to produce a quantitative profile. With no constraints there are a huge number of fittable parameters (every species concentration at every depth) and reliable results cannot be obtained. Introducing reasonable constraints (as may be expected, or already known, for wafer processing thin film structures ), such as sharp interfaces, known layer ordering, and fixed compound stoichiometry, can reduce the number of parameters to the point where the required accuracy of the experimental data ( separation of signal intensity from background; exclusion of data where elastic scattering becomes an issue) necessary to give reliable fits can be achieved. However, owing to the exponentially decreasing contribution to the total signal strength with depth, this cannot be extended beyond about 2λ in depth (which means 40 -50Å ) and, in addition, the true depth resolution possible is poor.
Examples of the successful use, and the misuse, of the ARXPS approach for the types of ultra-thin film structures found in wafer processing ( involving Si, SiO2, Si3N4, SiOxNy, Hf oxide based layers, and TaN) will be presented. In practical situations, where the intended recipient of the end results is not an an XPS "afficionado", communication of the data in a form that does not lead to gross over-interpretation remains an issue.