Transport and Optical Characteristics of Al-rich AlO Film and its Application to a Nonvolatile Memory

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1056-HH11-57

Transport and Optical Characteristics of Al-rich AlO Film and its Application to a Nonvolatile Memory Shunji Nakata1, Shingo Nagai2, Minoru Kumeda2, Takeshi Kawae2, Akiharu Morimoto2, Yoshitada Katagiri1, and Tatsuo Shimizu2 1 NTT Microsystem Integration Laboratories, 3-1 Morinosato Wakamiya, Atsugi, 243-0198, Japan 2 Grad. School of Natural Sci. & Tech., Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan ABSTRACT We propose the new process for fabricating Al-rich Al2O3 thin film, which is used as a charge storage layer for non-volatile Al2O3 memory. Nanoscale Al-rich thin film is deposited using RF magnetron co-sputtering by setting an Al metal plate on an Al2O3 target. Al-rich Al2O3 shows a larger conduction current in I-V characteristics and larger optical absorption than stoichiometric Al2O3 due to the increased electron trap sites. The C-V characteristics of the Alrich Al2O3 thin film show a large hysteresis window due to the charge trapping effect in the Alrich structure. INTRODUCTION Nanoscale devices have been widely studied [1, 2] for large-scale integration. In particular, silicon-oxide-nitride-oxide-silicon (SONOS) trap memory devices [3] have been attracting increasing attention because they are expected to provide low-voltage-writing operation and extremely large-scale integration due to their thin tunnel insulator. Recent studies have shown that using Al2O3 for the blocking insulator instead of SiO2 leads operation at much lower voltage [4]. Usually, Al2O3 is fabricated by atomic layer deposition (ALD) or metal organic chemical vapor deposition (MOCVD). However, there remain some problems, such as the presence of residual carbon and the high cost of the fabrication apparatus and gas material. We have been trying sputtering methods for the fabrication to overcome the problems. Recently electron-cyclotron-resonance (ECR) sputtering has been used to fabricate a novel non-volatile Al2O3 memory with an Al-rich structure as a charge storage layer [5-7]. However, ECR-sputtering requires the use of a large magnetic coil. In the present work, we succeeded in fabricating Al-rich Al2O3 thin film using a RF magnetron co-sputtering method where a few Al metal plates are set on the Al2O3 target and used the Al-rich Al2O3 as a charge storage layer for non-volatile Al2O3 memory. The fabricated Alrich Al2O3 layer shows larger conduction current characteristics and larger optical absorption than Al2O3. The high-frequency capacitance-voltage (C-V) measurement of Al2O3 thin film with the Al-rich Al2O3 layer shows a large hysteresis window due to an increase in electron trap sites in the Al-rich Al2O3 layer.

EXPERIMENT In the experiment, we used Al2O3 as a target of the RF magnetron sputtering to fabricate Al2O3 insulator. Ar gas was used for sputtering. The RF voltage and power were 2 kV and 200 W, respectively. The distance between the target electrode and the substrate electrode was about 4 cm. The substrate temperature was 200 oC. For the fabrication of Al-rich Al2O3, a few Al metal plates were set