| AVS 66th International Symposium & Exhibition | |
| Applied Surface Science Division | Tuesday Sessions |
| Session AS+BI+RA-TuM |
| Session: | Quantitative Surface Analysis III/Other Surface Analysis Methods |
| Presenter: | Ludovic Goffart, ST Microelectronics/LTM/CEA-LETI, France |
| Authors: | L. Goffart, ST Microelectronics/LTM/CEA-LETI, France C. Vallée, Laboratoire des Technologies de la Microélectronique (LTM), France B. Pelissier, LTM, Univ. Grenoble Alpes, CEA-LETI, France J-P. Reynard, ST Microelectronics, France D. Benoit, ST Microelectronics, France G. Navarro, CEA-LETI, France |
| Correspondent: | Click to Email |
This work is focusing on the oxidation of the well-known GST material (Ge2Sb2Te5, GST225) widely used in storage optics like CD, DVD and Blu-ray. This time, we use the GST for its electrical properties to create a non-volatile memory. The GST we use in this work is modified from the GST225 chemical composition to comply with the specifications needed in automotive applications, the most important being a good stability and cycling at high temperature environment.
This non stoichiometric GST composition leads to instability in its structure, therefore more aging and oxidation which conflict with the objectives of this new PCM cell. Added to this is some atomic segregation during crystallographic relaxation, which leads to low cycling durability of the cell and lower crystallization temperatures. To counter these effects, the GST material is doped but this makes more complex the chemical characterization of the material.
To understand and overcome these problems, different GST materials (from 225 to Ge rich) have been characterized using the pARXPS technique which is an angular resolved XPS. With this technique a very complete chemical characterization of the surface of these samples have been performed to gather useful information of atomic segregations and surface oxidation, by acquiring 8 simultaneous angles at the same time for different element windows. This is only possible by developing a complex fitting model for the large amount of spectra obtained. This model has to deal with the complex feature of the spectra obtained since some peaks were overlapping. Physical constraints are then necessary to obtain a realistic fit of the spectra. Once the model optimized, the aging of the samples have been studied by monitoring the evolution of specific XPS shapes with time. As a result, the oxidation kinetic and the thickness of the oxidized surfaces are quantified and finally a depth profile reconstruction of the different chemical bonds is performed. In addition to pARXPS, TEM-EDX analysis were performed to confirm the fitting model developed and profile depth reconstruction obtained with pARXPS technique.