Thin film deposition for next generation DRAM structures ISPR 2017 13.09.2017 J. Torgersen, F. Berto, F. Prinz, W. Cai NTNU Trondheim/ Stanford University
NTNU 10/16/2017 40000 students 50 faculties Nobel prize winner 2014
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NTNU Team Our group: 3 Faculty 10 PhD students 15 Master Students/ year Addlab, Fatigue and Nanolab ~ Supported by workshop and admin staff Research Directions: Material Design Material Property Prediction Surface and Interface Science Biocompatible Implants Light weight components Protective Coatings 10/16/2017
Atomic Layer Deposition- Motivation Moore s law One of humanity s greatest achievements Over 40 years of exponential improvement What is the limit? 10/16/2017
Atomic Layer Deposition- Motivation 10/16/2017 How to Increase the Capacitance? U = 1 2 CV 2 C = e 0 e r A d
Atomic Layer Deposition- Motivation Smallest die size: 0.683 mm 0.683 mm at the 90 nm 151.527 dies Average die size 2.130 mm 2.130 mm at the 65 nm 1434 dies Biggest die size: 20.253 mm 20.253 mm at the 65 nm 127 dies Core i3-2310e Transistors: 624 million Die size: Average (149 mm²) 10/16/2017
Atomic Layer Deposition- The principle Surface reactive sites Precursor pulse H 2 O oxidant Oxidant pulse 8
Atomic Layer Deposition- Scale Up Crossflow Single Injector Self-limiting nature enables easy scale up Showerhead 9
Atomic Layer Deposition- Scale Up ASM A400C Batch size of 125 8-inch wafers Dual tube for material stacks Process line integration Different wafer sizes processable Major applications for silicon nitride, amorphous silicon, doped polysilicon Wide range of metals and dielectrics processable http://www.asm.com/publishingimages/solutions/products/low-pressure-chemicalvapor-deposition-and-diffusion-products/advance-vertical-furnace/a412-plus.png 10
Atomic Layer Deposition- Scale Up Solaytec Wafer moves back and forth performing 4 cycles at a time 8 depositions/s with one head 5000 wafers/h Atmospheric pressure, no pump required Deposition rate 1nm/s per module Only TMA and H 2 O so far http://www.solaytec.com/images/stories/flexicontent/l_solaytec-2919-v1.jpg 11
Atomic Layer Deposition- The materials Depositing elements all across the periodic table Period 1 I A 18 VIII A 1 1s H 2 II A 13 III A 14 IV A 15 V A 16 VI A 17 VII A He 2 2s Li Be 2p B C N O F Ne 3 3s Na Mg 3 III B 4 IV B 5 V B 6 VI B 7 VII B 8 VIII B 9 VIII B 10 VIII B 11 I B 12 II B 3p Al Si P S Cl Ar 4 4s K Ca 3d Sc Ti V Cr Mn Fe Co Ni Cu Zn 4p Ga Ge As Se Br Kr 5 5s Rb Sr 4d Y Zr Nb Mo Tc Ru Rh Pd Ag Cd 5p In Sn Sb Te I Xe 6 6s Cs Ba 5d Hf Ta W Re Os Ir Pt Au Hg 6p Tl Pb Bi Po At Rn 7 7s Fr Ra 6d Rf Db Sg Bh Hs Mt Ds Rg Cn 7p Uut Fl Uup Lv Uus Uuo lanthanides (rare earth metals) 4f La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu actinides 5f Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Intel s 45-nm high-k transistor Nanoprobe for protein detection in cells Thin film solid oxide fuel cell 500 nm Mistry, K. et al, Electron Devices Meeting, 2007. IEDM 2007. IEEE International, pp.247-250 Shambat et al.; Nano Lett. 2013, 13, 4999-5005. Chao, C. C., Hsu, C. M., Cui, Y., Prinz, F. P., ACS Nano, 5, 5692-5696 (2011).
High-k thin films for DRAMs How to Increase the Capacitance? U = 1 2 CV 2 C = e 0 e r A d 13
High-k materials C = e 0 e r A d 14
Leakage current High-k thin films for DRAMs Dielectric constant Pt top electrode evaporation Amorphous? Pt Pt Pt T-ALD BTO p-si Al (200 nm) Poly Crystalline P. Schindler et al., Scripta Mater. (2015) 15
High-k thin films for DRAMs (a) (b) (c) Crystallites buried in amorphous matrix of 7 nm thick BaTiO 3 P. Schindler et al., Scripta Mater. (2015) 16
High-k thin films for DRAMs Reaction limited Diffusion limited Recombination limited s << 1 r = 0 AR independent s = 1 r = 0 AR dependent s independent r > 0 AR dependent Knoops et al. J. El. Chem. Soc. 2010 17
High-k thin films for DRAMs GPC ~ 0.45 Å/cycle Acharya, Torgersen et al 2016 J. o. Material Chemistry C 18
High-k thin films for DRAMs Thickness (Å ) Thickness (Å ) 60 (a) (b) 50 50 40 40 30 20 30 10 20 1 2 3 0 0 2 4 6 8 10 No. of precursor exposures No. of H 2 O pulses Self-limiting mode of growth in both half cycles of reaction Acharya, Torgersen et al 2016 J. o. Material Chemistry C 19
High-k thin films for DRAMs Period 1 I A 18 VIII A 1 1s H 2 II A 13 III A 14 IV A 15 V A 16 VI A 17 VII A He 2 2s Li Be 2p B C N O F Ne 3 3s Na Mg 3 III B 4 IV B 5 V B 6 VI B 7 VII B 8 VIII B 9 VIII B 10 VIII B 11 I B 12 II B 3p Al Si P S Cl Ar 4 4s K Ca 3d Sc Ti V Cr Mn Fe Co Ni Cu Zn 4p Ga Ge As Se Br Kr 5 5s Rb Sr 4d Y Zr Nb Mo Tc Ru Rh Pd Ag Cd 5p In Sn Sb Te I Xe 6 6s Cs Ba 5d Hf Ta W Re Os Ir Pt Au Hg 6p Tl Pb Bi Po At Rn 7 7s Fr Ra 6d Rf Db Sg Bh Hs Mt Ds Rg Cn 7p Uut Fl Uup Lv Uus Uuo lanthanides (rare earth metals) 4f La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu actinides 5f Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 20
Reprinted with permission from: An et al. ACS Appl. Mater. Interfaces 2014 Data from Schindler et al. Scr. Mat. 2016 Modified from Hayashi et al. Jpn. J. Appl. Physics 1994 1000 900 800 700 r 600 500 400 300 200 200 250 300 350 400 450 500 550 600 Thickness Thickness 45 40 RuO2 SiO2 35 Dielectric Constant 30 25 20 Substrate ε r Ba/Ti ratio 15 10 0.40 0.45 0.50 0.55 0.60 0.65 Composition [Ti/(Ba+Ti)] Postdeposition treatment Torgersen et al 2016 J.o. Physical Chemistry Letters 21
ALD characterization in the SSRL What is the chemical and structural nature for thin film performance modifications? Provides Chemical Identity Oxidation State Coordination Local geometric Structure Local Density of unoccupied States XANES Quantum Simulations Allows studying Interfaces Structural distortions Dopant atoms Nucleation process Torgersen et al 2016 J.o. Physical Chemistry Letters 22
ALD characterization in the SSRL Photoelectron E= hv - binding energy Ejected to unoccupied state Photo e- Auger e- Ev B X-ray with energy hv Fluorescent photon A Beer s law: Absorbance= log(i 0 /I t ) or log(i 0 /I f ) 23
X-ray absorption near edge structure (XANES) Absorption (normalized) Pre-edge: Molecular symmetry Forbidden transitions Weak intensity Featureless 2 Post-edge: Multiple scattering paths Photo e- longer than Zn-S bond Zn-S-Zn ZnS_300 1 0 2460 2470 2480 2490 2500 2510 Enegy (ev) Edge-jump: Oxidation state Unoccupied state in valence orbitals Empty S 3p and Zn 4 sp orbitals 24
XANES of ALD BTO Mixing of BaO and TiO 2 to form BaTiO 3 vs. Torgersen et al 2016 J.o. Physical Chemistry Letters 25
XANES of ALD BTO Ba Rich Ti Rich Stoichiometric Changing Ba/Ti composition vs. vs. Torgersen et al 2016 J.o. Physical Chemistry Letters 26
XANES of ALD BTO Leakage current and band gap (b) Ti rich Stoichiometry Ba rich Density of States (a.u) 0 2 4 6 E (ev) Torgersen et al 2016 J.o. Physical Chemistry Letters 27
Atomic percentage (%) High-k thin films for DRAMs 1 Top Bottom side 2 Ti Ba 3 80 Aspect ratio of the trench ~ 1:3.9 Step coverage (d bottom /d top ) ~ 90% Uniform composition distribution. 60 40 20 0 1 2 3 Positions Acharya, Torgersen et al 2016 J. o. Material Chemistry C 28
Summary ALD for reaching the ultimate limit in downascaling ALD high-k Barium Titanate for next generation DRAM structures Novel chemistry for self limiting growth of BTO Explanation of dielectric properties with electronic structure revealed by synchroton based X-ray absorption Shinjita Yongmin Ioannis Anup
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