Electrical Characteristics of Anatase-TiO 2 Films by Low Temperature Fabrication M. Kimura 1 , T. Nabatame 2 , H. Yamada 1 , A. Ohi 2 , T. Chikyow 2 and T. Ohishi 1 1 Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan Phone: +81-29-860-4915 E-mail: KIMURA.Masayuki@nims.go.jp 2 MANA Foundry and MANA Advanced Device Materials Group, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan 1. Introduction It has been reported that CMOS fabricated by the gate-last process at a low temperature are being mass pro- duced. Future scaling of CMOS technology requires a higher-k dielectrics (k >30). Several approaches have been reported to obtain cubic-HfO 2 with a high k value by spe- cific annealing process with fast ramping-up [1, 2]. TiO 2 is one of the most promising candidates of higher-k materials because of a high k value and low temperature crystalliza- tion. In this paper, we present characterization of anatase-TiO 2 films fabricated by ALD and PDA processes, and discuss the Vfb change due to oxygen transfer in TiO 2 film by annealing in oxidation and reduction conditions. 2. Experimental The TiO 2 films with 3-6 nm thicknesses were deposited on SiO 2 /Si(100) and SiO 2 /Si(111) by the ALD process at 200 ºC using Ti(NMe 2 ) 4 precursor and H 2 O gas. The PDA was performed at 300-500 C for 30 sec in O 2 . TiO 2 MOS capacitors with TaC and Pt gate electrodes were fabricated. MOS capacitors with Al 2 O 3 and HfO 2 dielectrics were also prepared to discuss the Vfb shift. All capacitors were an- nealed at 400 C in 3% H 2 (FGA). The oxygen transfer in TiO 2 layer was controlled by using the catalytic effect of the Pt as follows: To remove oxygen from TiO 2 layer, FGA was carried out at 400-500 C in 3% H 2 . To introduce oxy- gen into TiO 2 layer, oxidation annealing (ODA) was per- formed at 100-300 C for 1-200 min in O 2 . 3. Results and Discussion 3.1 Physical characterizations of TiO 2 films The peaks of C and N impurities in as-deposited TiO2 film are undetectable by angle-resolved XPS analysis, as shown in Fig. 1. The typical XRD patterns of as-deposited and annealed TiO2 films are shown in Fig. 2. We found that the TiO2 film consists of anatase structure at temperature above 300 C. Fig. 3 shows capacitance equivalent thick- ness (CET) as a function of TiO2 thickness on Si(100) and Si(111). The anatase-TiO2 films were prepared by PDA at 500 C. The k values in Si(100) and Si(111) samples are estimated 35 and 32, respectively. This demonstrates that the anatase-TiO2 films which formed at low annealing temperature (500 C) show a significant high k value (>30). 3.2 Vfb shift due to oxygen transfer in TiO 2 layer Fig. 4 shows C-V characteristics of TaC-gated MOS capacitors with SiO2, TiO2, HfO2 and Al2O3 dielectrics. The C-V curve of TiO2 capacitor slightly shifts toward pos- itive direction in comparison with SiO2 capacitor. Fig. 5 summarizes Vfb behaviors of several high-k dielectrics. All high-k dielectrics occurs positive Vfb shift compared with SiO2. Note that the value of the positive Vfb shift in high-k dielectrics can be ordered as follows: Al2O3 (0.72 V) > HfSiO x (0.36 V) [3] > HfO2 (0.29 V) > TiO2 (0.08 V). It is well known that the Vfb shift of high-k CMOS predomi- nantly occurs due to the bottom interface dipole at high-k/SiO2 interface [4, 5]. A schematic illustration of band diagram of TaC/high-k/SiO2/Si stack structure is shown in Fig. 6. The Vfb shift of each dielectric relates to the strength of the bottom interface dipole of each one. Fig. 7 shows the relationship between the normalized Vfb and the ODA temperature for TiO2 MOS capacitors with Pt and TaC gate electrodes. The Vfb of the Pt-gated MOS capacitors shifts in the positive direction as the ODA temperature increases, while the Vfb of TaC-gated MOS capacitors shows an almost constant value. No difference of the C-V curve and Vfb behaviors between Si(100) and Si(111) samples appears regardless of the ODA temperature. This indicates that the orientation of Si substrate doesn’t affect to the Vfb shift. To investigate the influence of the oxygen transfer in the TiO2 layer on the Vfb shift, we ex- amined the annealing time dependence of the Vfb shift, as shown in Fig. 8. The C-V curves of capacitor shift in the positive direction with increasing the annealing time (an inset graph). The Vfb change in ODA at 250 C saturates at ODA times above 4 min. In contrast, none of the Vfb value in ODA at 150 C is saturated even after annealing for 200 min. These results suggest that the oxygen diffusion in TiO2 layer affects to the Vfb shift as previously reported [6]. Fig. 9 shows the change of Vfb for TiO2, HfO2 [6] and HfSiO x [6] dielectrics after ODA at 300 C and FGA at 500 C. The positive and negative Vfb shifts for all samples appear in ODA and FGA treatments, respectively. We found that the TiO2 dielectric shows the maximum and minimum Vfb change after ODA and FGA, respectively. This strongly indicates that the oxygen transfer of the TiO2 dielectric is faster than those of HfO2 and HfSiO x dielectrics. 4. Conclusions We demonstrate that anatase-TiO2 films, which formed in low temperature fabrication process, show a significant high dielectric constant of 35. We found that the Vfb of TiO2 capacitor shifts slightly toward positive direction in comparison of SiO2. Note that the oxygen transfer in TiO2 layer relates to the Vfb shift from results in ODA and FGA. References [1] S. Migita et al., IEDM Tech. Dig. (2010) p.269. [2] S. Nakajima et al, ECS-Trans. 28, (2010) p.203. [3] P. Homhuan et al., Jpn. J. Appl. Phys. 50, 10PA03(2011). [4] K. Kita et al., Appl. Phys. Lett. 94, 132902(2009). [5] K. Iwamoto et al., Appl. Phys. Lett. 92, 132907(2008). [6] T. Nabatame et al., Thin solid Films 520, 3387(2012). -26- Extended Abstracts of the 2012 International Conference on Solid State Devices and Materials, Kyoto, 2012, pp26-27 PS-1-10