Improvement in Electrical Characteristics of ALD Al 2 O 3  Film by Microwave Excited Ar/O 2 Plasma Treatment

Introduction High-k material is becoming important to manufacture of integrated circuits [1-3]. Especially, Al 2 O 3 is expected for the gate dielectric film of power devices [4] and Metal Insulator Metal (MIM) capacitor [3]. Atomic Layer Deposition (ALD) is an effective method for forming conformal thin dielectric films. In a recent study, using Al 2 O 3 film formed by ALD at low temperature, less variation in the electrical characteristics could be obtained compared with that formed at high temperature [3]. However, large flat-band voltage shift was shown because of low oxidation ability by H 2 O at low temperature. In order to solve this problem, it is shown that Post Deposition Process (PDP) is an effective way [3]. It is considered that the microwave excited plasma oxidation is candidate for PDP because it has the strong oxidizing capability [5]. However, the electrical characteristics were degraded because the Al 2 O 3 /substrate interface was oxidized by the excess strong plasma oxidation in former study [6]. In this paper, we report the effects on the microwave excited Ar/O 2 plasma treatment to the electrical characteristics of Al 2 O 3 MIS capacitor. ALD and PDP were carried out continuously in the same chamber at low temperature to suppress the oxidation. Experiment MIS capacitors were fabricated on n-type Si(100) wafers with resistivity of 8-12 Ωcm. The active region was formed by thermal oxidation and etching using the buffered HF with surfactant. After the native oxide on the active region was removed by 0.5% diluted HF, 10nm Al 2 O 3 was formed by Trimethylaluminium (TMA)/H 2 O ALD process at stage temperature of 75 o C. The microwave excited Ar/O 2 plasma treatment was carried out as PDP just after the ALD-Al 2 O 3 formation in the same chamber. The PDP conditions are as follows: stage temperature was 75 o C, process time was 1min, Ar flow rate was 200sccm and 2.45GHz microwave power was 800W. The pressure and O 2 flow rate at PDP were varied as experimental parameter. We choose the weaker oxidation capability of all PDP conditions than former one [6] in this experiment. Finally, aluminum films were deposited as top and bottom electrode by evaporation. Results and Discussion Figs.1(a) and (b) show C-V characteristics for the case of bias swept negative to positive and positive to negative, respectively. From Fig.1(a), flat-band voltage without PDP is -2.23V. It indicates the existence of positive fixed oxide charges. In all samples with PDP