| AVS 61st International Symposium & Exhibition | |
| Materials Characterization in the Semiconductor Industry Focus Topic | Monday Sessions |
| Session MC+AP+AS-MoM |
| Session: | Characterization of 3D Structures, 2D films and Interconnects |
| Presenter: | Eugenie Martinez, CEA, LETI, MINATEC Campus, France |
| Authors: | E. Martinez, CEA, LETI, MINATEC Campus, France B. Saidi, STMicroelectronics, France P. Caubet, STMicroelectronics, France F. Piallat, STMicroelectronics, France H. Kim, CEA, LETI, MINATEC Campus, France S. Schamm-Chardon, CEMES-CNRS, France R. Gassilloud, CEA, LETI, MINATEC Campus, France |
| Correspondent: | Click to Email |
Down-scaling of CMOS transistors beyond the 14 nm technological node requires the implementation of new architectures and materials. The gate last integration scheme is a promising solution to better control the threshold voltage of future MOSFETs, because of its low thermal budget [1]. Advanced characterization methods are needed to gain information about the chemical composition of such structures. The analysis of thin layers and interfaces buried under a thick metal electrode is particularly challenging. An effective approach based on backside sample preparation is proposed here.
To tune the work-function toward nMOS values, the technology currently investigated is based on HfO2 for the dielectric and a thin TiN layer capped by a TiAl alloy for the gate [2]. For a better understanding of aluminium and other elements redistributions after a 400°C annealing, a specific methodology has been developed based on the removal of the Si substrate. It allows to achieve XPS and Auger analyses from the backside of the sample [3].
In particular, Auger depth profiling performed on HfO2/TiN/TiAl/TiN/W gate stacks at low energy (500 eV Ar+) brought the following main conclusions: a) no Al diffusion toward the HfO2/TiN interface, b) nitrogen out diffusion in the upper TiAl film, c) significant oxygen scavenging. By comparison, these results evidenced that Auger frontside analyses suffer from sputter-induced artifacts.
In a further study, to understand the behavior of nitrogen out diffusion in the TiAl layer, we deposited TiAlNx thin films with various nitrogen flows by reactive sputtering deposition and performed backside XPS analyses. At low/medium nitrogen flows, which correspond to the TiAlNx film after TiN/TiAl bilayer anneal, the N1s core level spectra obviously shows that N is mainly bonded to Al rather than Ti. Results are compared with frontside XPS performed with a thinner TiN upper layer. The backside approach is shown to be more representative of the technological stack, in particular with respect to the TiN oxidation.
Measurements were carried out at the NanoCharacterization Platform (PFNC) of MINATEC.
[1] C. L. Hinkle et al., Appl. Phys. Let. 100, 153501 (2012).
[2] A. Veloso et al.., Symposium on VLSI Technology, Digest of Technical Papers (2011).
[3] M. Py et al., AIP conference proceedings 1395, 171 (2011).