Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014)
    Thin Films Tuesday Sessions
       Session TF-TuP

Paper TF-TuP10
Effect of Al Doping on Crystallization and Electrical Property of CeO2 Films Deposited by RF Magnetron Sputtering

Tuesday, December 9, 2014, 4:00 pm, Room Mauka

Session: Thin Films Poster Session
Presenter: Keiji Ishibashi, COMET Inc., Japan
Authors: K. Ishibashi, COMET Inc., Japan
T. Okazaki, Hosei University, Japan
H. Kamata, Hosei University, Japan
Y. Notani, Hosei University, Japan
K. Hara, Hosei University, Japan
T. Osawa, Hosei University, Japan
K. Aoki, Hosei University, Japan
K. Fujiyama, Hosei University, Japan
S.-G. Ri, COMET Inc., Japan
S. Suzuki, COMET Inc., Japan
Y. Yamamoto, Hosei University, Japan
Correspondent: Click to Email
To suppress crystallization of CeO2 thin films as a gate stack material in MOS devices, Al was doped in CeO2 films during radio frequency (RF) magnetron sputtering deposition on p-type Si (100) substrates. Deposition was carried out at room temperature in an Ar atmosphere of 5.3 Pa to a typical thickness of 35 nm using a CeO2 target on which some Al metal plates were bonded. The composition of the resultant deposited films measured by X-ray photoelectron spectroscopy was Ce0.28Al0.06O0.66, equivalent to (CeO2)0.9(Al2O3)0.1 in terms of the molar fraction. The post annealing was performed in air and N2 in the temperature range from 200 to 600°C. Addition of aluminum oxide with 10% molar fraction into CeO2 during sputter deposition was effective in suppressing crystallization. The deposited films remained amorphous after annealing up to 500°C from observation of X-ray difraction and transmission electron diffraction. The interfacial SiO2 layer was grown after annealing in both ambients of air and N2. While after annealing in air the interface consisted of a simple double layer of CeO2/SiO2/Si, a lower oxide such as Ce2O3 was formed between CeO2 and SiO2 in an N2 annealing ambient. The leakage current measured at the applied electric field of 1 MV/cm (gate voltage=3.5 V) was decreased to as low as the order of 10-8 and 10-7 A/cm2 after annealing at 200°C in air and N2, respectively. The C-V hysteresis of the samples annealed in air was broadened with the increase of annealing temperature. Annealing in N2 reduced C-V hysteresis in contrast to air annealing, but appearance of a kink and gradual slope in the depletion state on its C-V curves suggested the existence of a large amount of shallow states originated from the lower Ce oxide at the interface. The flat band voltage after annealing was shifted toward higher gate voltages due to the fixed negative charge arising from Al oxides. The Al doping in CeO2 was effective in suppressing crystallization of CeO2 films, but introduced complicated behavior in I-V and C-V electrical characteristics, while in the non-doped CeO2 films electrical neutrality of the interfacial lower Ce oxide (Ce2O3) was maintained and led to relatively simple behavior in electrical characteristics.