Passivation of Ge surface treated with trimethylaluminum and investigation of electrical properties of HfTiO/Ge gate stacks

doi:10.1016/j.jmst.2017.04.021

Abstract

Abstract:

In the current work, in situ surface passivation Ge substrate by using trimethylaluminum (TMA) prior to HfTiO films deposition and electrical properties of HfTiO/Ge gate stacks have been investigated by X-ray photoelectron spectroscopy (XPS) and electrical measurements systematically. Based on analysis from XPS measurements, it has been confirmed that the interfacial layer of HfTiO/Ge gate stack has been suppressed effectively after 20 half-ALD cycles TMA pretreatment. Electrical properties of metal-oxide-semiconductor (MOS) capacitor based on HfTiO gate dielectrics have shown that the MOS capacitor with 20 cycles TMA cleaning exhibits the lowest interface state density (～7.56 eV^-1 cm^-2) and the smallest leakage current (～2.67 × 10^-5 A/cm²). Correspondingly, the leakage current conduction mechanisms for MOS capacitor device with 20 cycles TMA cleaning also have been discussed in detail.

Key words: Germanium, Trimethylaluminum, Atomic layer deposition, Electrical properties

Gao Juan, He Gang, Xiao Dongqi, Jin Peng, Jiang Shanshan, Li Wendong, Liang Shuang, Zhu Li. Passivation of Ge surface treated with trimethylaluminum and investigation of electrical properties of HfTiO/Ge gate stacks[J]. J. Mater. Sci. Technol., 2017, 33(8): 901-906.

Figures/Tables 10

Table 1 Ge substrates with different surface pretreatment processes.

Substrate	Pretreatment process
S1	Unpretreated
S2	10 cycles of TMA(0.2 s)/N₂(8 s) half-ALD-cycle purge
S3	20 cycles of TMA(0.2 s)/N₂(8 s) half-ALD-cycle purge
S4	1 nm Al₂O₃ passivation layer

Fig. 1. XPS spectra of Hf 4f core level at the interface between HfTiO films and Ge substrates with different surface pretreatment processes: (a) S1, (b) S2, (c) S3, (d) S4.

Fig. 2. XPS spectra of O 1s core level at the interface between HfTiO films and Ge substrates with different surface pretreatment processes: (a) S1, (b) S2, (c) S3, (d) S4.

Fig. 3. XPS spectra of Ge 3d core level at the interface between HfTiO films and Ge substrates with different surface pretreatment processes: (a) S1, (b) S2, (c) S3, (d) S4.

Fig. 4. C-V characteristic curves of all samples, corresponding to different surface pretreatment processes, i.e., uncleaned (S1), 10 cycles TMA (S2), 20 cycles TMA (S3), and 1 nm-thick Al2O3 barrier layer (S4), respectively.

Table 2 Parameters extracted from C-V curvesof all samples, corresponding to different surface pretreatment processes, i.e., uncleaned (S1), 10 cycles TMA (S2), 20cycles TMA (S3), and 1 nm-thick Al2O3 barrier layer (S4), respectively.

Samples	E_ot (nm)	k	N_bt ( × 10¹¹ cm^-2)	Q_ox ( × 10¹² cm^-2)	D_it ( × 10¹² eV^-1cm^-2)	J (A/cm²)
S1	1.89	18.5	1.37	-5.95	7.65	1.79 × 10^-2
S2	1.92	18.2	0.57	-3.63	8.55	6.36 × 10^-4
S3	1.56	22.6	1.11	-3.53	7.56	2.67 × 10^-5
S4	1.71	20.5	0.50	-5.67	7.84	1.03 × 10^-4

Fig. 5. J-V characteristic curves of all samples, corresponding to different surface pretreatment processes, i.e., uncleaned (S1), 10 cycles TMA (S2), 20 cycles TMA (S3), and 1 nm-thick Al2O3 barrier layer (S4), respectively.

Fig. 6. Conduction mechanism fitting of the MOS capacitor with 20 cycles TMA cleaning Ge substrate under gate injection: (a) Schottky emisson, (b) P-F emission, (c) FN tunneling.

Fig. 7. Conduction mechanism fitting of the MOS capacitor with 20 cycles TMA cleaning Ge substrate under substrate injection: (a) P-F emission, (b) FN tunneling.

Fig. 8. Band diagram of Al/HfTiO/Ge with 20 cycles TMA cleaning Ge substrate calculated by F-N tunneling.

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