| AVS 59th Annual International Symposium and Exhibition | |
| Nanomanufacturing Science and Technology Focus Topic | Monday Sessions |
| Session NM+NS+MS+EM-MoA |
| Session: | ALD and Scalable Processes for Nanomanufacturing |
| Presenter: | F. Piallat, ST Microelectronics, France |
| Authors: | F. Piallat, ST Microelectronics, France V. Beugin, CEA Grenoble, France R. Gassilloud, CEA Grenoble, France P. Michallon, CEA Grenoble, France L. Dussault, LTM - MINATEC - CEA/LETI, France B. Pelissier, LTM - MINATEC - CEA/LETI, France C. Leroux, CEA Grenoble, France P. Caubet, ST Microelectronics, France C. Vallée, LTM - MINATEC - CEA/LETI, France |
| Correspondent: | Click to Email |
Sub-20 nm high-k/metal CMOS devices require about 2 nm thin metal gate electrode with adapted work function (WF) and chemical inertness regarding the high-k dielectric sub-layer. TaCN material deposited by Plasma Enhanced Atomic Layer Deposition (PE-ALD) has been investigated as a possible gate electrode candidate [1-2]. Depending on the carbon content TaCN can presents a p-type behavior with a WF from 4.5 to 4.7eV [3]. Besides plasma used for deposition may have an impact on the under-layer dielectric such as an increase of the EOT [4]. A deviation from bulk material characteristics of the metal gate WF is induced by the intimate bond linking environment at high-k/TaCN interface, but these chemical mechanisms are still unclear. Thus, in this work, interface of TaCN and HfO2 dielectric is carefully analyzed by X-Ray Photoelectron Spectrometry (XPS), using Ta4f, Hf4f, O1s, C1s, N1s and Si2p core levels, and obtained bonding environments are correlated to work function extracted from MOS capacitors.
Thanks to chemical stability of SiO2 [5], bonding environments of TaCN/SiO2 and HfO2/SiO2 stacks were chosen as reference for XPS analysis. Then, by comparing TaCN deposited on HfO2 spectra with these references, the evolution of the chemical environments can be determined, thus a mechanism of interaction between the two materials is proposed. Furthermore, it appeared that, when deposited on HfO2, TaCN oxidation is higher than on SiO2, which is attributed to the higher capacity of HfO2 to have O deficiency [6].
In addition, TaCN/HfO2/SiO2 stack was measured using Parallel Angle Resolved XPS (PARXPS) in order to build a depth composition profile. This profile confirms the modifications of chemical environment such as oxidation of the electrode close to high-k/metal interface, it also shows N penetration in HfO2, which could be induced by plasma densification.
Finally, electrical results from MOS capacitors with TaCN/HfO2/SiO2 stacks and TiN/W plug have shown an evolution of the p-like metal flat band voltage (Vfb) with plasma conditions. The modifications of chemical bonding environment observed at the high-k/metal interface can give insight on this deviation of Vfb with plasma.
[1] W. S. Hwang, D. Chan, B. Jin Cho, IEEE Transactions on Electron Devices, 55, (2008)
[2] H. Zhu and R. Ramprasad, Journal of Applied Physics 109, 083719 (2011)
[3] H. N. Alshareef, et al., Electrochemical and Solid-State Letters, 11, H182 (2008)
[4] H. C. Shin and C. Hu, Semiconductor Science Technologie, 11, 463, (1996)
[5] M. Zier, et al., Applied Surface Science 252, 234 (2005)
[6] G. D. Wilk, R. M. Wallace and J. M. Anthony, Journal of Applied Physics 89, 5243 (2001)