Title: Electrical Properties of Al<sub>2</sub>O<sub>3</sub> Incorporated CeO<sub>2</sub> Thin Films Deposited by RF Magnetron Sputtering
Abstract: High-k materials have been widely investigated as a new gate stack in metal-oxide-semiconductor (MOS) devices 1,2) because leakage current through the conventional SiO2 gate increases as scaling down of MOS devices. Among them, CeO 2 is one of the most noteworthy materials 3) because of its high dielectric constant of 26, chemical stability and the promising interfacial properties owing to the compatibility with Si in terms of the crystal structure and the lattice constant: the cubic fluoric structure, lattice mismatch as small as 0.35%. Cerium dioxide is, however, likely to crystalize even just after RF magnetron sputtering deposition at room temperature, leading to the increase of the leakage current along with grain boundaries 4) . In our preliminary study, we found that the thin films of Al 2 O 3 doped CeO 2 (Al 2 O 3 as 10% composition) was kept amorphous after annealing up to 500 °C in a N 2 atmosphere. In this work, we will report the electrical properties of the Al 2 O 3 incorporated CeO 2 to suppress the poly-crystallization of the films as a function of the wide Al 2 O 3 composition range. The oxide composite of CeO 2 and Al 2 O 3 was prepared by the RF magnetron sputtering equipped with the combinatorial mask system 5) . The deposition was carried out using 2 targets of CeO 2 and Al 2 O 3 with the applied RF powers of 150 and 200 W, respectively, in an Ar atmosphere with an O 2 introduction (10%) at room temperature at a pressure of 0.5 Pa. We prepared the combinatorial composition spread thin films, with the total thickness of 32 nm, in which Al 2 O 3 composition ratio was changed in the range of 0 ~ 60% against CeO 2 in a sample. In the deposition process, we repeated the following procedures 80 times; first, 0.16 nm thick CeO 2 layer deposition: second, a wedge shaped CeO 2 layer deposition with a thickness of 0 to 0.24 nm by the moving mask: finally, a wedge shaped Al 2 O 3 layer with a thickness of 0 to 0.24 nm by the mask moving to the counter direction. After the deposition, we prepared 2 kinds of samples; one was annealed in a N 2 atmosphere, the other in an O 2 atmosphere at 500 °C for 30 minutes. Then, Pt dot electrodes were formed using the metal mask with the 100 µm in diameter openings on the surface of the annealed samples by sputtering. The electrical properties were characterized by I-V and C-V measurements. For the sample annealed in a N 2 atmosphere, the leakage current density obtained from I-V characteristics at the electric field of -1 MV/cm decreased from around 1.0 × 10 -6 to the minimum value of 1.0 × 10 -8 A/cm 2 with increasing Al 2 O 3 composition from 0 to 20%. When the Al 2 O 3 composition increased above 20% up to 60%, however, the leakage current density approached back to the value without Al 2 O 3 doping. For the O 2 annealed sample, the annealing effect was limited; the minimum leakage current density was around 1.0 × 10 -7 A/cm 2 at the Al 2 O 3 composition of 10%. The leakage current density was greater than that without Al 2 O 3 doping at the doping level excess 20%. From the result of C-V measurement at 1 MHz, the estimated dielectric constant of the films, assuming the interfacial SiO 2 layer with a thickness of 3.5 nm, was rapidly decreased from 18 to 8 with the increase of the Al 2 O 3 composition from 0 to 15%. For the higher Al 2 O 3 composition than 15%, the estimated dielectric constant represented a constant value of 8. Judging from both view points of the leakage current and the dielectric constant, the optimum Al 2 O 3 composition was considered to lie around 8%. Compared with the annealing in N 2 , the O 2 annealing was not effective in improving electrical properties. REFERENCES 1) Wei Wang, Ning Gu, J. P. Sun and P. Mazumder, Solid-State Electronics 50 , 1489-1494 (2006). 2) Dedong Han, Jinfeng Kang, Changhai Lin and Ruqi Han, Microelectronic Engineering 66 , 643-647 (2003). 3) D. G. Lim, G. S. Kang, J. H. Yi, K. J. Ynag and J. H. Lee, Journal of the Korean Physical Society 51 , 1085-1088 (2007). 4) H. Y. Lee, S. I. Kim, Y. P. Hong, Y. C. Lee, Y. H. Park and K. H. Ko, Surface and Coatings Technology 173 , 224 (2003). 5) M. L. Green, K.-S. Chang, S. DeGendt, T. Schram and J. Hattrick-Simpers, Microelectronic Engineering 84 , 2209–2212 (2007).
Publication Year: 2016
Publication Date: 2016-09-01
Language: en
Type: article
Indexed In: ['crossref']
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