AlON thin films formed by ECR plasma oxidation for high-k gate insulator application
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AlON thin films formed by ECR plasma oxidation for high-k gate insulator application Go Yamanaka, Takafumi Uchikawa, Shun-ichiro Ohmi and Tetsushi Sakai Department of Information Processing, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan ABSTRACT AlON thin films formed by the electron cyclotron resonance (ECR) plasma oxidation of the AlN thin films deposited on p/p+-Si(100) by the ECR sputtering method were investigated for high-k gate insulator application. The leakage current density was found to be decreased with the ECR plasma oxidation of the AlN thin films. Furthermore, the equivalent oxide thickness (EOT) of 1.5 nm with the leakage current density of 5.1x10-4 A/cm2 (@Vfb-1 V) was obtained after the 1000oC rapid thermal annealing (RTA) because of the high quality interfacial layer formation. INTRODUCTION According to the ITRS, the gate dielectrics need to be scaled down below 0.9 - 1.4 nm for 90 nm-node CMOS technology and beyond. Although the actual scaling limit of SiO2 is still in debate, the high-k gate dielectrics, such as ZrO2, HfO2, Al2O3, are investigated by many institutions [1]. Among these materials, Al2O3 is an attractive material as gate dielectrics due to its excellent thermal stability in contact with Si, high dielectric constant (k=10), wide energy bandgap (8.3 eV) and so on [2-5]. However, Al2O3 has some problems, such as the existence of the flat-band voltage (Vfb) shift and the interfacial layer formation with relatively low dielectric constant, which would increase the equivalent oxide thickness (EOT) during the post deposition annealing (PDA) process. In this paper, AlON high-k thin films formed by the electron cyclotron resonance (ECR) plasma oxidation of the AlN thin films deposited on p/p+-Si(100) by the ECR sputtering method were investigated. AlN thin films would be expected to suppress the interfacial layer formation during the ECR plasma oxidation and/or the PDA processes [6]. EXPERIMENTAL DETAILS AlN thin films (3 - 4 nm) were deposited on p/p+-Si(100) at room temperature by the ECR plasma sputtering. The pressure in the chamber during the deposition was 9x10-2 Pa with Ar/N2 flow rates of 20/6 sccm. Then the deposited AlN thin films were oxidized by Ar/O2 ECR plasma for 15 - 120 s to form the AlON thin films with Ar/O2 flow rates of 20/8 sccm. The p/p+ -Si(100) wafers were cleaned in H2SO4/H2O2 and subsequently dipped in dilute HF (HF-Last Si). In order to investigate the effect of the surface treatment, the chemical oxide layer (0.6 nm) was formed by preserving the Si wafers in H2O2 for 60 min (chemically oxidized Si). The deposited films were annealed in vacuum (10-4 Pa) at 600oC for 3 min. The rapid thermal annealing (RTA) was also carried out at 400 - 1000oC for 1 min in flowing N2 ambient. Finally, Al was
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deposited ex-situ as a top electrode by vacuum evaporation method. C-V was measured in the 10 k - 1 MHz range by the precision LCR meter (HP 4284A) and J-V wa
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