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Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation

Lixing Zhou1, Jinjuan Xiang2, , Xiaolei Wang2, and Wenwu Wang2

+ Author Affiliations

 Corresponding author: Jinjuan Xiang, xiangjinjuan@ime.ac.cn; Xiaolei Wang, wangxiaolei@ime.ac.cn

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Abstract:

Ge has been an alternative channel material for the performance enhancement of complementary metal–oxide–semiconductor (CMOS) technology applications because of its high carrier mobility and superior compatibility with Si CMOS technology. The gate structure plays a key role on the electrical property. In this paper, the property of Ge MOSFET with Al2O3/GeOx/Ge stack by ozone oxidation is reviewed. The GeOx passivation mechanism by ozone oxidation and band alignment of Al2O3/GeOx/Ge stack is described. In addition, the charge distribution in the gate stack and remote Coulomb scattering on carrier mobility is also presented. The surface passivation is mainly attributed to the high oxidation state of Ge. The energy band alignment is well explained by the gap state theory. The charge distribution is quantitatively characterized and it is found that the gate charges make a great degradation on carrier mobility. These investigations help to provide an impressive understanding and a possible instructive method to improve the performance of Ge devices.

Key words: Ge MOSFETozone oxidationgate chargesmobility



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Fig. 1.  (a) GeOx thickness with oxidation time at temperature varying from 80 to 400 °C. (b) Arrhenius plots for linear and parabolic region. Ea is activation energy.

Fig. 2.  (Color online) (a) Capacitance–voltage curves of W/TiN/Al2O3/GeOx/Ge capacitor. (b) Dit values at 0.3 eV above Ev for different GeOx thickness and the inset shows the Dit energy distribution of W/TiN/Al2O3/GeOx/Ge capacitors with different GeOx thickness.

Fig. 3.  (Color online) XPS spectra of Ge 3d for GeOx/Ge for different GeOx thickness. The takeoff angel in (a)–(d) is 90° (normal to the sample surface) and it is 35° in (e).

Fig. 4.  (Color online) (a) The trend of area intensity ratio of Ge1+, Ge2+, Ge3+, and Ge4+ to Ge0 with different GeOx thickness. (b) The area intensity ratio of Ge2+/Ge1+, Ge3+/Ge1+, Ge4+/Ge1+ and Ge3+/Ge2+ at the takeoff angle of 35° and 90°.

Fig. 5.  (Color online) The XPS measurements of the valence band and core-level spectra of (a) bulk Al2O3 and (b) Ge substrate.

Fig. 6.  (Color online) The XPS measurements of core-level spectra for different Al2O3 thickness: (a) 2 nm, (b) 4 nm, and (c) 6 nm.

Fig. 7.  (Color online) The dependence of VBO of the Al2O3/Ge interface on Al2O3 thickness.

Fig. 8.  The energy band sketch of Al2O3/Ge structure (a) before and (b) after contact.

Fig. 9.  The dependence of VBO of Al2O3/Ge structure on interlayer GeOx thickness.

Fig. 10.  (Color online) The relationship of VFB and EOT of Al/Al2O3/GeOx/Ge capacitors with different (a) GeOx and (b) Al2O3 thickness.

Fig. 11.  (Color online) (a) The charge distribution and (b) the charge density in the Al/Al2O3/GeOx/Ge structure.

Fig. 12.  (Color online) (a) The relationship of VFB and EOT and (b) charge density at Ge/GeOx interface of Al/Al2O3/GeOx/Ge capacitors with and without O2 annealing.

Fig. 13.  The area intensity ratio of Al 2p to O 1s in Al2O3 with different Al2O3 thickness.

Fig. 14.  (Color online) The charge density at (a) the Ge/GeOx and (b) GeOx/Al2O3 interface for different ambient annealing. (c) and (d) are dipole and corresponding charge density at the GeOx/Al2O3 interface for different ambient annealing.

Fig. 15.  (Color online) The core level spectra of Ge 3d and Al 2p of Ge/GeOx/Al2O3 structure without PDA and with PDA in N2, O2, H2, and NH3 ambients.

Fig. 16.  The energy band schematic of the Ge/GeOx/Al2O3 structure (a) without dipole, (b) with a positive dipole, and (c) negative dipole at the GeOx/Al2O3 interface.

Fig. 17.  (Color online) (a) IdVg curves and (b) hole mobility versus inversion carrier density of Ge pMOSFET with different GeOx thickness measured at 77 K.

Fig. 18.  (Color online) Hole mobility versus inversion carrier density of Ge pMOSFET for different PDA ambients measured at 300 K.

Fig. 19.  (Color online) A sketch of remote Coulomb scattering from charges in the gate stack.

Fig. 20.  (Color online) Gate leakage current of Ge/0.7 nm GeOx/4 nm Al2O3/Al capacitors for different PDA ambients.

[1]
Kobayashi M, Thareja G, Ishibashi M, et al. Radical oxidation of germanium for interface gate dielectric GeO2 formation in metal-insulator-semiconductor gate stack. J Appl Phys, 2009, 106, 104117 doi: 10.1063/1.3259407
[2]
Takagi S, Zhang R, Suh J, et al. III–V/Ge channel MOS device technologies in nano CMOS era. Jpn J Appl Phys, 2015, 54, 06FA01 doi: 10.7567/JJAP.54.06FA01
[3]
Otani Y, Itayama Y, Tanaka T, et al. Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques. Appl Phys Lett, 2007, 90, 142114 doi: 10.1063/1.2720345
[4]
Maeda T, Nishizawa M, Morita Y, et al. Role of germanium nitride interfacial layers in HfO2/germanium nitride/germanium metal-insulator-semiconductor structures. Appl Phys Lett, 2007, 90, 072911 doi: 10.1063/1.2679941
[5]
Kim K H, Gordon R G, Ritenour A, et al. Atomic layer deposition of insulating nitride interfacial layers for germanium metal oxide semiconductor field effect transistors with high-κ oxide/tungsten nitride gate stacks. Appl Phys Lett, 2007, 90, 212104 doi: 10.1063/1.2741609
[6]
Hashemi P, Hoyt J L. High hole-mobility strained- Ge/Si0.6Ge0.4 P-MOSFETs with high-K/metal gate: Role of strained-Si cap thickness. IEEE Electron Device Lett, 2012, 33, 173 doi: 10.1109/LED.2011.2176913
[7]
Chen W B, Chin A. High performance of Ge nMOSFETs using SiO2 interfacial layer and TiLaO gate dielectric. IEEE Electron Device Lett, 2010, 31, 80 doi: 10.1109/LED.2009.2035719
[8]
Matsubara H, Sasada T, Takenaka M, et al. Evidence of low interface trap density in GeO2/Ge metal-oxide-semiconductor structures fabricated by thermal oxidation. Appl Phys Lett, 2008, 93, 032104 doi: 10.1063/1.2959731
[9]
Xie Q, Deduytsche D, Schaekers M, et al. Effective electrical passivation of Ge(100) for HfO2 gate dielectric layers using O2 plasma. Electrochem Solid-State Lett, 2011, 14, G20 doi: 10.1149/1.3551461
[10]
Kuzum D, Krishnamohan T, Pethe A J, et al. Ge-interface engineering with ozone oxidation for low interface-state density. IEEE Electron Device Lett, 2008, 29, 328 doi: 10.1109/LED.2008.918272
[11]
Fukuda Y, Ueno T, Hirono S, et al. Electrical characterization of germanium oxide/germanium interface prepared by electron-cyclotron-resonance plasma irradiation. Jpn J Appl Phys, 2005, 44, 6981 doi: 10.1143/JJAP.44.6981
[12]
Fukuda Y, Yazaki Y, Otani Y, et al. Low-temperature formation of high-quality GeO2 interlayer for high-k gate dielectrics/Ge by electron-cyclotron-resonance plasma techniques. IEEE Trans Electron Devices, 2010, 57, 282 doi: 10.1109/TED.2009.2035030
[13]
Lee C H, Nishimura T, Nagashio K, et al. High-electron-mobility Ge/GeO2 n-MOSFETs with two-step oxidation. IEEE Trans Electron Devices, 2011, 58, 1295 doi: 10.1109/TED.2011.2111373
[14]
Zhang R, Iwasaki T, Taoka N, et al. High-mobility Ge pMOSFET with 1-nm EOT Al2O3/GeOx/Ge gate stack fabricated by plasma post oxidation. IEEE Trans Electron Devices, 2012, 59, 335 doi: 10.1109/TED.2011.2176495
[15]
Zhang R, Huang P C, Lin J C, et al. High-mobility Ge p- and n-MOSFETs with 0.7-nm EOT using HfO2/Al2O3/GeOx/Ge gate stacks fabricated by plasma postoxidation. IEEE Trans Electron Devices, 2013, 60, 927 doi: 10.1109/TED.2013.2238942
[16]
Zhang R, Lin J C, Yu X, et al. Examination of physical origins limiting effective mobility of Ge MOSFETs and the improvement by atomic deuterium annealing. IEEE Symposium on VLSI Technology, 2013, 26
[17]
Lee C H, Lu C, Nishimura T, et al. Thermally robust CMOS-aware Ge MOSFETs with high mobility at high-carrier densities on a single orientation Ge substrate. 2014 Symposium on VLSI Technology (VLSI-Technology), 2014, 1 doi: 10.1109/VLSIT.2014.6894394
[18]
Lee C H, Nishimura T, Lu C, et al. Dramatic effects of hydrogen-induced out-diffusion of oxygen from Ge surface on junction leak. IEEE International Electron Devices Meeting, 2014, 32.5.1 doi: 10.1109/IEDM.2014.7047156
[19]
Wang X L, Xiang J J, Wang S K, et al. Remote interfacial dipole scattering and electron mobility degradation in Ge field-effect transistors with GeOx/Al2O3 gate dielectrics. J Phys D, 2016, 49, 255104 doi: 10.1088/0022-3727/49/25/255104
[20]
Zhou L X, Wang X L, Ma X L, et al. Hole mobility degradation by remote Coulomb scattering and charge distribution in Al2O3/GeOx gate stacks in bulk Ge pMOSFET with GeOx grown by ozone oxidation. J Phys D, 2017, 50, 245102 doi: 10.1088/1361-6463/aa6f96
[21]
Zhang R, Lin J C, Yu X, et al. Impact of plasma postoxidation temperature on the electrical properties of Al2O3/GeOx/Ge pMOSFETs and nMOSFETs. IEEE Trans Electron Devices, 2014, 61, 416 doi: 10.1109/TED.2013.2295822
[22]
Esseni D, Abramo A. Modeling of electron mobility degradation by remote Coulomb scattering in ultrathin oxide MOSFETs. IEEE Trans Electron Devices, 2003, 50, 1665 doi: 10.1109/TED.2003.814973
[23]
Saito S I, Torii K, Shimamoto Y, et al. Remote-charge-scattering limited mobility in field-effect transistors with SiO2 and Al2O3/SiO2 gate stacks. J Appl Phys, 2005, 98, 113706 doi: 10.1063/1.2135878
[24]
Casterman D, de Souza M M. Evaluation of the Coulomb-limited mobility in high-κ dielectric metal oxide semiconductor field effect transistors. J Appl Phys, 2010, 107, 063706 doi: 10.1063/1.3319558
[25]
Kaushik V S, O'Sullivan B J, Pourtois G, et al. Estimation of fixed charge densities in hafnium-silicate gate dielectrics. IEEE Trans Electron Devices, 2006, 53, 2627 doi: 10.1109/TED.2006.882412
[26]
Ota H, Hirano A, Watanabe Y, et al. Intrinsic origin of electron mobility reduction in high-k MOSFETs - from remote phonon to bottom interface dipole scattering. 2007 IEEE International Electron Devices Meeting, 2007, 65 doi: 10.1109/IEDM.2007.4418864
[27]
Jha R, Gurganos J, Kim Y H, et al. A capacitance-based methodology for work function extraction of metals on high-k. IEEE Electron Device Lett, 2004, 25, 420 doi: 10.1109/LED.2004.829032
[28]
Wang X L, Han K, Wang W W, et al. Physical origin of dipole formation at high-k/SiO2 interface in metal-oxide-semiconductor device with high-k/metal gate structure. Appl Phys Lett, 2010, 96, 152907 doi: 10.1063/1.3399359
[29]
Wang X L, Han K, Wang W W, et al. Comprehensive understanding of the effect of electric dipole at high-k/SiO2 interface on the flatband voltage shift in metal-oxide-semiconductor device. Appl Phys Lett, 2010, 97, 062901 doi: 10.1063/1.3475774
[30]
Barraud S, Bonno O, Cassé M. The influence of Coulomb centers located in HfO2/SiO2 gate stacks on the effective electron mobility. J Appl Phys, 2008, 104, 073725 doi: 10.1063/1.2968217
[31]
Toniutti P, Palestri P, Esseni D, et al. On the origin of the mobility reduction in n- and p-metal-oxide-semiconductor field effect transistors with hafnium-based/metal gate stacks. J Appl Phys, 2012, 112, 034502 doi: 10.1063/1.4737781
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    Received: 18 May 2021 Revised: 21 June 2021 Online: Uncorrected proof: 03 September 2021Accepted Manuscript: 03 September 2021Published: 04 January 2022

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      Lixing Zhou, Jinjuan Xiang, Xiaolei Wang, Wenwu Wang. Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation[J]. Journal of Semiconductors, 2022, 43(1): 013101. doi: 10.1088/1674-4926/43/1/013101 L X Zhou, J J Xiang, X L Wang, W W Wang, Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation[J]. J. Semicond., 2022, 43(1): 013101. doi: 10.1088/1674-4926/43/1/013101.Export: BibTex EndNote
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      Lixing Zhou, Jinjuan Xiang, Xiaolei Wang, Wenwu Wang. Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation[J]. Journal of Semiconductors, 2022, 43(1): 013101. doi: 10.1088/1674-4926/43/1/013101

      L X Zhou, J J Xiang, X L Wang, W W Wang, Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation[J]. J. Semicond., 2022, 43(1): 013101. doi: 10.1088/1674-4926/43/1/013101.
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      Investigation on the passivation, band alignment, gate charge, and mobility degradation of the Ge MOSFET with a GeOx/Al2O3 gate stack by ozone oxidation

      doi: 10.1088/1674-4926/43/1/013101
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      • Lixing Zhou:received a Ph.D. degree in electronic engineering from University of Chinese Academy of Sciences, Beijing, China, in 2019. She joined School of Microelectronics, Beijing University of Technology since August 2019. She currently engaged in research of the interface property and mobility characteristics of Ge MOSFETs
      • Jinjuan Xiang:received a Ph.D. degree in electronic engineering from University of Chinese Academy of Sciences, Beijing, China, in 2016. She is currently an Associate Professor with the Institute of Microelectronics, Chinese Academy of Sciences. She is currently engaged in the research and development on atomic layer deposition for Nano CMOS application
      • Xiaolei Wang:received a Ph.D. degrees in electronic engineering from University of Chinese Academy of Sciences, Beijing, China, in 2013. He is currently a Professor with the Institute of Microelectronics, Chinese Academy of Sciences. He is currently engaged in research of high mobility Ge MOSFET and novel non-volatile field-effect transistors
      • Wenwu Wang:received a Ph.D. degree from Tokyo University, Tokyo, Japan, in 2006. He has been with the Institute of Microelectronics, Chinese Academy of Sciences, Beijing, China, since 2008. He is currently a Professor with the Institute of Microelectronics, Chinese Academy of Sciences. His current research interests cover Si/Ge-based processing and device technology, and novel 3D CMOS devices
      • Corresponding author: xiangjinjuan@ime.ac.cnwangxiaolei@ime.ac.cn
      • Received Date: 2021-05-18
      • Revised Date: 2021-06-21
      • Published Date: 2022-01-10

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