Presentation on theme: "Techniques of tuning the flatband voltage of metal/high-k gate-stack Name: TANG Gaofei Student ID: 20222159 The Hong Kong University of Science and Technology."— Presentation transcript:
Techniques of tuning the flatband voltage of metal/high-k gate-stack Name: TANG Gaofei Student ID: 20222159 The Hong Kong University of Science and Technology
Outline Motivation Device Fabrication A simple metal/high-k stack process flow Techniques of tuning flatband voltage Workfunction High-k dielectric Fabrication condition Summary 2
3 Miniaturize the MOSFET by scaling coefficient SizeScaling coefficient L1/k ε1 tox1/k NA NDK Xj1/k W VT1/k * To ensure constant electric field  S. M. Sze, Kwok K. Ng. Physics of semiconductor devices (2008)
4 Why high-k? The thinner oxide will induce more gate leakage! Equivalent Oxide Thickness (EOT) A thinner high-k layer can be equivalent to a thicker SiO2 Gate dielectricAl2O3HfO2La2O3SiO2 Bandgap (eV)7-188.8.131.52 Dielectric Constant920273.9 Other high-k materials: ZrO2, Y2O3, Ta2O5, TiO2, etc  Takashi Ando. Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging? Materials. P.478-500 (2012)
5 Poly-Si has a relatively higher resistivity Boron penetration phenomenon Vth control by changing doping density Bad interface quality between poly and high-k material Common materials for gate electrodes: TiN, TaN, W, Mo, NiSi, etc. Why not poly but metal? Poly-Si close to oxide layer may appear depletion
6 Source/Drain implantation FOX formation N+ SiNx P-Si (100) Gate dielectricAl2O3HfO2La2O3 Bandgap (eV)7-95.64.3 Dielectric Constant92027 Crystallization Temp ( ℃ ) <800500350 Fabrication of NMOSFET with metal/high-k stacks
7 Source/Drain implantation FOX formation High-k film deposition High-k material This step should be in-situ to avoid moisture absorption, because some materials like La2O3 has bad hygroscopic immunity. Fabrication of NMOSFET with metal/high-k stacks
8 Source/Drain implantation FOX formation High-k film deposition Gate electrode formation E-beam evaporation Fabrication of NMOSFET with metal/high-k stacks
9 Source/Drain implantation FOX formation High-k film deposition Gate electrode formation E-beam evaporation Etching, RTA Fabrication of NMOSFET with metal/high-k stacks
10 Source/Drain implantation FOX formation High-k film deposition Gate electrode formation E-beam evaporation Etching, RTA PR Coating Active region lithography Photo Resist Fabrication of NMOSFET with metal/high-k stacks
11 Source/Drain implantation FOX formation High-k film deposition Gate electrode formation E-beam evaporation Etching, RTA Source/drain electrode, liftoff PR Coating Active region lithography Fabrication of NMOSFET with metal/high-k stacks
12 Flatband voltage analysis Here, Φ m, Φ s, Q ox, and C ox are the effective metal WF, semiconductor WF, fixed charges in a dielectric film, and capacitance of a dielectric film. C ～ V Curve
13 Tuning technique 1 EWF control via different gate metal CV characteristics of TmSiO/HfO2 samples employing different gate metals Flatband voltage versus EOT for TmSiO/HfO2 capacitors employing different gate metal  E. Dentoni Litta, et al. Effective workfunction control in TmSiO/HfO2 high-k/metal gate stacks. ULIS, p.69 (2014) Flatband voltage shift with gate metal changing.
14 Tuning technique 2 Modulating effective workfunction (EWF) of gate electrode by impurity doping Case: Doping for NiSi-gate electrode  J. Kedzierski, et al. Threshold voltage control in NiSi-gated MOSFETs through silicidation induced impurity segregation (SIIS). TED. V. 52, N.1, p.39 (2005)
15 Tuning technique 3 Tuning crystalline microstructures in metal gate electrode.  K. Ohmori, et al. Wide Controllability of Flatband Voltage by Tuning Crystalline Microstructures in Metal Gate Electrodes. IEDM. p. 345 (2007).
16  H. C. WEN, et al. Issues associated with p-type band-edge effective work function metal electrodes: Fermi-level pinning and flatband roll-off. VLSI Symp. p. 160 (2007).  G. Bersuker, et al. Origin of the Flat-Band Voltage (Vfb) Roll-Off Phenomenon in Metal/High-k Gate stacks. ESSDERC. p. 134 (2008) Tuning technique 4 Changing the equivalent oxide thickness Roll-Off Model 1.R-O increases with higher electrode WF and thicker high-k film. 2.R-O is slightly greater on p-type substrates.
17 Tuning technique 5 Double dielectric films (HfO2/La2O3) It has been reported that La2O3 and Sc2O3 produce negative shift in VFB with respect to HfO2 reference Manabu Adachi. A Novel Flat Band Voltage Tuning for Metal/High-k Gate Stack Structure. Tokyo Institute of Technology, Master thesis (2005) Y. Kim, et al. Electrical characteristics of high-k La2O3 thin film deposited by e-beam evaporation method. Electrochemical Society. Volume 22 (2003)
18 Tuning technique 6 Mixed High-k Incorporation at HfO2/SiO2 Interface When changing concentration of La2O3 from 0 to 1, the ΔV FB can be 0.48V.
19 Tuning technique 6 Mixed High-k Incorporation at HfO2/SiO2 Interface When changing concentration of Sc2O3 from 0 to 1, the ΔV FB can be 0.15V.
20 Tuning technique 7 Anneal temperature changing  K. Ohmori, et al. Influences of annealing in reducing and oxidizing ambients on flatband voltage properties of HfO2 gate stack structures. Journal of Applied Physics, v. 101 (2007) FGA: Forming gas anneal OGA: Oxidizing gas anneal With a FGA process, the values of V fb are almost constant, regardless of the difference in WF, mainly due to a complete Fermi level pinning. After an additional OGA process, the largest V fb observed in a temperature range of 250–400 degree is 0.34 V, which is smaller than the WF difference of 0.8 eV.
21 Summary Techniques of tuning the flatband voltage of metal/high-k gate-stack Metal modulation What metal? What doped in metal? What metal crystalline? High-k dielectric modulation Dielectric EOT modulation Multi-layer high-k materials Mixed high-k materials incorporated Fabrication condition Anneal temperature