Ta-doped modified Gd2O3 film for a novel high k gate dielectric

doi:10.1016/j.jmst.2019.05.028

Abstract

Abstract:

Gadolinium oxide (Gd₂O₃) film has potential as a candidate gate dielectric to replace HfO₂. In this work, we provide a simple method by trace Ta ($\widetilde{1}$%) doping to significantly improve the dielectric properties of Gd₂O₃ film. And effects of annealing temperatures of Ta-doped Gd₂O₃ (GTO) films are investigated in detail. Results show that GTO film annealed at 500 °C exhibits excellent performance as a novel gate dielectric material for integrated circuit, showing a small surface roughness of 0.199 nm, a large band gap of 5.45 eV, a high dielectric constant (k) of 21.2 and a low leakage current density (J_g) of 2.10 × 10^-3 A/cm². All properties of GTO films are superior to pure Gd₂O₃ films and these GTO films meet the requirements for next-generation gate dielectrics. In addition, impedance spectrum is first used to analyze the equivalent circuit of GTO based metal-oxide-semiconductor (MOS) capacitors, which represents a new insight to understand observed electrical behaviors.

Key words: Rare earth oxides, High k film, Magnetron sputtering, Annealing temperature, Gate dielectrics

Shuan Li, Yanqing Wu, Guoling Li, Hongen Yu, Kai Fu, Yong Wu, Jie Zhang, Wenhuai Tian, Xingguo Li. Ta-doped modified Gd₂O₃ film for a novel high k gate dielectric[J]. J. Mater. Sci. Technol., 2019, 35(10): 2305-2311.

Figures/Tables 8

Fig. 1. Flow chart for preparation of MOS capacitors.

Fig. 2. (a) TEM image of $\widetilde{5}$ nm GTO-0 film, (b) SEM image of GTO film thickness for electrical performance test, (c, d, e) EDS mapping of GTO-0 thin films and (f) XRD patterns of GTO and Gd2O3 thin films.

Fig. 3. AFM images of (a) Gd2O3-500 film, (b, c, d, e, f) GTO-T film and (g) Ra of Gd2O3-500 and GTO-T (T = 0, 400, 500, 600 and 700 °C) films.

Fig. 4. (a) Optical absorption and band gap of Gd2O3-500 film, (b) optical absorption and (c, d, e, f, g) Tauc plots of GTO-T (T = 0, 400, 500, 600 and 700 °C) films and (h) band gaps of Gd2O3-500 and GTO-T (T = 0, 400, 500, 600 and 700 °C) films (α: absorption coefficient; h: Planck constant; υ: frequency of light).

Fig. 5. (a) Schematic diagram of magnetron co-sputtering GTO film as well as GTO and Gd2O3 based MOS capacitors, (b) C-V and I-V curves of GTO-500 and Gd2O3-500 samples, (c) C-V, (d) I-V curves and (e) k value and Jg value change chart of GTO-T (T = 0, 400, 500, 600 and 700 °C) samples.

Table 1 Parameters extracted from C-V curves (Cox: accumulation capacitances; Cfb: flat band capacitance; Qox: equivalent oxide-charge density; EOT: equivalent oxide thickness).

Sample	C_ox (nF)	k	C_fb (nF)	V_fb (V)	Q_ox (cm^-2)	EOT (nm)
GTO-700	24.09	15.6	2.04	0.21	2.83×10¹²	5
GTO-600	28.29	20.4	2.07	0.16	3.60×10¹²	3.8
GTO-500	29.46	21.2	2.07	-0.13	5.45×10¹²	3.7
GTO-400	24.15	17.4	2.04	-0.68	1.29×10¹²	4.5
GTO-0	9.72	7.0	1.81	-1.77	4.97×10¹²	11.1
Gd₂O₃-500	23.40	16.8	2.04	-0.28	5.03×10¹²	4.6

Fig. 6. (a) Nyquist plots, (b, c) θ and |Z| as a function of frequency (the inset in (c) shows the equivalent circuit), (d, e, f, g) fitting curves of GTO-400, GTO-500, GTO-600 and GTO-700 samples and (h) values of R2 as a function of annealing temperature (Z’: real part of impedance; Z’’: imaginary part of impedance; θ: phase angle).

Table 2 Parameters extracted from equivalent circuit.

Sample	R₁ (Ω)	R₂ (Ω)	CPE₂-T (F)	CPE₂-P
GTO-700	49.37	576.6	1.88×10^-7	0.77
GTO-600	50.79	3004	7.37×10^-8	0.82
GTO-500	49.97	5272	4.62×10^-8	0.83
GTO-400	51.38	3156	2.87×10^-9	0.91

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Ta-doped modified Gd₂O₃ film for a novel high k gate dielectric

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