ALD deposited ferroelectric HfO 2 S. Slesazeck 1, U. Schroeder 1, E. Yurchuk 1, J. Müller 2, S. Müller 1, D. Martin 1, T. Schenk 1, C. Richter 1,C. Adelmann 3, S. Kalinin 5, A. Kersch 7, and T. Mikolajick 1,4 1 3rd ALD Symposium - SEMICON Europa October 7 th, 2014 2 3 5 6 7 1
Outline 1. Motivation: Ferroelectricity in HfO 2 2. Stabilization of the Ferroelectric HfO 2 Phase 3. Device Application: 1T FeFET Memory 4. Summary 2
Outline 1. Motivation: Ferroelectricity in HfO 2 2. Stabilization of the Ferroelectric HfO 2 Phase 3. Device Application: 1T FeFET 4. Summary 3
Motivation: Ferroelectric HfO 2 Ferroelectrics enable fast low power non-volatile memories 130nm FRAM e.g. FRAM: - current scaling limit: 130 nm due to material properties new material necessary TI & Ramtron A lot of industry experience CMOS sub 30 nm DRAM integrating g HfO 2 / ZrO 2: - CMOS compatible - scalability well below 50nm - ALD process available chipworks - ferroelectric properties (IEDM 2011 / VLSI 2012 / IEDM 2013) 4
Motivation: 1T FeFET memory Performance advantages: non-volatility non-destructive readout low power consumption switching speed in ns-time range low operation voltages Metal-Gate Ferroelectric Semiconductor n+ n+ no polarization p-substrate t Idrain 1 0 low Vth high Vth Vgate 5
Motivation: 1T FeFET memory Metal-Gate Performance Ferroelectric + - - - + advantages: Semiconductor n+ + + + n+ non-volatility p-substrate t non-destructive readout low power Idrain 0 consumption switching speed in high Vth ns-time range low operation voltages Vgate 6
Motivation: 1T FeFET memory Metal-Gate Performance Ferroelectric advantages: non-volatility Semiconductor non-destructive readout low power Idrain 1 consumption low Vth switching speed in ns-time range low operation voltages - + - + - + - - - n+ n+ p-substrate t Vgate 7
Outline 1. Motivation: Ferroelectricity in HfO 2 2. Stabilization of the Ferroelectric HfO 2 Phase 3. Device Application:1T FeFET 4. Summary 8
HfO 2 phase stabilization Anneal + Doping Amorphous HfO 2 2 Anneal 1 Low-symmetry / lower-k phase + Doping High-symmetry / high-k phases Non-centrosym. / Non-centrosym. / FE phase AFE phase Spinodal 4 De-mixing Cubic Fm3m or Orthorhombic Pbc2 1 Tetragonal P4 2 /nmc depending on dopant Tetragonal* Monoclinic P2 1 /c 1 Tetragonal/Cubic 14 Si 38 Sr 39 Y 13 Al 40 Zr 64 Gd 14 Si 13 Al 9
ALD Process: doped HfO 2 nanolaminates Other precursors used for dopant supercycles: tetrakis(ethylmethylamino)hafnium (TEMAHf) hafnium tetrachloride (HfCl 4 ) silicon tetrachloride (SiCl 4 ) Pt Ti TiN Pt Ti TiN tetrakis(dimethylamino)silane (4DMAS) tris(dimethylamino)silane (3DMAS) HfO 2 SiO 2 tris(isopropylcyclopentadienyl)gadolinium (Gd( i PrCp) 3 ) tris(methylcyclopentadienyl)-yttrium (Y(MeCp) 3 ) TiN Native SiO 2 Si- wafer strontium di-tert-butylcyclopentadienyl (Sr( t Bu 3 Cp) 2 ) and trimethylaluminium (TMA) + water, ozon or O 2 -plasma 10
Capacitor Route Route Layer depositi on Anneal + Pt Wet Etch dots Silicon Electrode Deposition HfO 2 deposition Platinum dots Simple capacitor processing 11
Effect of Si -Doping lacement [ C C/cm2] Electric Disp Capac citance [ F/c cm2] 12 60 40 20 0-20 -40-60 4.5 4.0 35 3.5 3.0 2.5 2.0 1.5 Electric Field [MV/cm] Para FE AFE SiO 2 0 mol % 4.4 mol % 5.6 mol % 6.6 mol % 8.5 mol % -3 0 3-3 0 3-3 0 3-3 0 3-3 0 3 0 mo % SiO 2 4,4 mol % 9 nm 5,6 Si:HfO mol % 2 after 6,6 mol 800 % o C 8,5 Anneal mol % -3 0 3-3 0 3-3 0 3-3 0 3-3 0 3 Electric Field [MV/cm] Pt TiN Si:HfO 2 TiN Si-substrate Increase of Si content concentration Change of electrical properties : Effect was confirmed by polarisation and capacitance -voltage measurements P r ~ C(V)dV E. Yurchuk et al., Thin Solid Films 2012 A. Toriumi at al. APL 86, 2006
Correlation to HfO 2 phase C. Richter BALD 2014 Ferroelectricity observed when orthorhombic h phase dominant 13
Different HfO 2 dopants dopant range paraelectric antiferroelectric ( ( ) ferroelectric P paraelectric 0 0 E Ferroelectricity visible for dopands with different crystal radius Antiferroelectricity only for dopands with radius smaller than HfO 2 Dopant range larger for higher crystal radius Schroeder et al., JSS 2012/JJAP 2014 14
Different HfO 2 dopants - polarization Maximum polarization i typically at about 3-6 mol% dopant concentration Schroeder et al., JJAP 2014 15
Outline 1. Motivation: Ferroelectricity in HfO 2 2. Stabilization of the Ferroelectric Phase 3. Device Application: 1T FeFET 4. Summary 16
Ferroelectric Device Application: Field Effect 1T Transistor FeFET 28nm N-channel MFIS-FET Memory Window 20 nm liner W (ma) Dra ain current 10 + - + - + - n+ + - + - + - n+ L G : 28 nm 1 +5V 100 ns I TH erase 0.1 MW program -5V 100 ns 001 0.01 1E-3 - + - + - + n+ - + - + - + n+ -1.0 10-0.5 05 00 0.0 05 0.5 10 1.0 15 1.5 Gate bias (V) World s first 28nm FeFET Memory window ~1V 17 E. Yurchuk et al., IEEE TED 2014
Device Application: 1T FeFET Endurance Retention 0.5 ~09V 0.9V K. Khullar Master Thesis V V V) Volts) TH t (V 0.0-0.5-1.0-1.5 25 o C 85 o C 125 o C MW after 10 years (V) 1.2 0.9 0.6 03 0.3 25 o C 0.0 85 o C 125 o C 10 years -2.0 10-1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 Time (s) Time (s) E. Yurchuk et al., IEEE TED 2014 Memory window after 10 5 cycles: ~0.9V Accumulation of asymmetric ti charge injection closes MW Detrap pulse can recover memory window Memory window after 10 years: ~1.0V 18
Device Application: 1T FeFET Endurance Ferroelectric FET Ferroelectric MIM Cap ~09V 0.9V K. Khullar Master Thesis K. Yurchuk PhD Thesis Cycling in capacitor limited it by breakdown Cycling in transistor limited by charge trapping 19
Device Endurance Application: 1T FeFET Endurance Ferroelectric FET Gate leakage current ~09V 0.9V I 2 G (A/cm ) 0.1 Number of program/erase cycles: initial 5x10 3 1E-3 100 10 4 10 3 2x10 4 1E-5 2x10 3 5x10 4 1E-7 K. Khullar Master Thesis -2-1 0 1 2 V G (V) E. Yurchuk et al., IPRS 2014 Gate leakage current increases with program/erase cycling 20
Device Application: 1T FeFET Interfacial traps I m 2 CP (ma/cm ) 250 200 150 100 50 0 Variable base level charge pumping N CP (Traps/cm m 2 ) 10 x10 11 5 0 10 0 10 1 10 2 10 3 10 4 Number of cycles initial after 5x10 3 cycles after 2x10 3 cycles after 10 3 cycles -2-1 0 1 V GB (V) E. Yurchuk et al., IPRS 2014 Generation of interface traps is the root cause of degradation Interplay between SiO2-interface and ferroelectric HfO has to be optimized 21
DRAM like FeFET: CH Cheng et al. IEEE EDL 35, 1, 2014-30nm ZrHfO in FeFET: +/- 4V switching Switching in sub-cycles - Switching time: 5ns 10 12 endurance, but low retention: ~10s Changed operation conditions can significantly improve cycling 22
Comparison NOR Flash vs. AND FeFET NOR Flash AND FeFET DRAM DRAM spec FeFETFET Write/Erase Speed 1μs/2ms 10 ns/10ns ns 5ns Read Speed 10μs 20ns ns? Retention 10 yrs 10 yrs >64ms 10s Endurance 10 5 cycles 10 4 cycles >10 15 >10 12 Write/Erase Voltage 10-20V 5V 0.5V 4V FeFET meets some FLASH and DRAM specifications 23
Scaling of FeFET grain and domain size Grain size ~30nm TEM Domain size ~300nm Domains and grains before Domains Domains device and grains and grains structuring underneath underneath PFM 250nm device 25nm device - Scaling likely l possible, but needs to be checked - low variability of switching characteristics on smallest devices 24
Piezo Force Microscopy Dielectrics Piezoelectrics Pyroelectrics Ferroelectrics Ref.: http://en.wikipedia.org/wiki/ Piezoresponse_Force_Microscopy - Local distribution - Phase: Polarization direction detectable D. Martin @ Oak Ridge Nat. Labs 25
Piezo Force Measurements 3 nm nm 2 1 a.u. +4.2 V -4.2 V 180 0 0-180 Topography Piezo responce Phase polarization value visible two polarization direction - Most HfO 2 grains switchable - PFM serves as base for optimization of film composition D. Martin et al., Adv. Mat. submitted U. Schroeder et al., IWDTF 2013/ and crystallization on simple capacitor structures JJAP 2014 26
Outline 1. Motivation: Ferroelectricity in HfO 2 2. Stabilization of the Ferroelectric HfO 2 Phase 3. Ferroelectric Switching Behavior 4. Device Application: 1T FeFET 5. Summary 27
Summary Material: A ferroelectric phase in HfO 2 thin films can be stabilized Ferroelectric phase most likely orthorhombic phase Several stabilizing dopants have been identified Ferroelectric Devices: 1T/1C: FE-HfO 2 adds the 3rd dimension to FRAM scaling World s first 28nm FeFET device HfO 2 -based FeFET added to ITRS roadmap in 2014: Most promising Emerging Memory concept FeFET meets already some DRAM and FLASH specification Superior control of dopant concentration in ALD nanolaminates and usbsequent crystallization of the film is mandatory 28
Thank you for your attention This work was supported in part by the EFRE fund of the European Commission within the scope of technology development and in part by the Free State of Saxony (Project: Cool Memory, Heiko, Merlin) and by funding of the Deutsche Forschungs Gemeinschaft(DFG) (Project: Inferox) 29
Thanks to the FeFET TEAM: 2 3 4 5 6 7 8 9 and many more: U. Schröder 1, E. Yurchuk 1, J. Mueller 2, S. Mueller 1, T. Mikolajick 1 T. Boescke 4, D. Martin 1, D. Zhou 1, J. Sundqvist 2, P. Polakowski 2, T. Schenk 1, U. Boettger 5, D. Braeuhaus 5, S. Starschich 5, C. Adelmann 6, M. Popovici 6, T. Schloesser 3, M. Trentzsch 3, M. Goldbach 3, R.v. Bentum 3, S. Knebel 1, T. Olsen 1, R. Hoffmann 2, J. Paul 2, R. Boschke 3, A. Kumar 7, T.M. Arruda 7, S.V. Kalinin 7, M. Alexe 8, A. Morelli 8, A.Kersch 9, R. Maverick 9 30 1