© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name 2008 First-principle study of thin metallic films annealed on crystalline «high- к » oxide Fabien Fontaine-Vive Pierre-Yves Prodhomme Philippe Blaise

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© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name MOS transistor evolution in microelectronics Downscaling limitation: Leakage current due to tunneling effect => replacing SiO2 by high-k (high permittivity) dielectric HfO2 BUT unpredictable threshold voltage of the metal gate beyond Schottky model => First approach, oxide pin the metal Fermi level - Surface states (Bardeen 1 ) - MIGS (Metal Induced Gap States) (Louie 2, Hobbs 3 ) - surface defects, charge trap (Spicer 4 ) The distribution of the gap states is characteristic of the oxide, ONLY ! 1 Phys. Rev., (1947), 71, Phys. Rev. B, (1977), 15, IEEE Trans. Elect. Devices, (2004), 51, J. Vac. Sci. Tec., (1979), 16, Phys. Rev. Lett., 1984, 52, Phys. Rev. B, 2006, 74 Not sufficient, realistic simulations => depend on interfacial dipoles - Interface structure (Tung 5 ) - surface stoechiometry (Fonseca 6 ) Fabien Fontaine-Vive

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© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Construction of the metal-oxide interfacial supercell, two approaches: stacking arbitrary crystalline surfaces together, suitable for close crystallographic arrangement Ex: cubic metal staking on cubic oxide Fmax ~ eV/A + Cubic metal crystal Cubic HfO2 = Supercell relaxation But ! How stacking different crystalline phases like a cubic phase stacking on a monoclinic highk oxyde m-HfO2 Fabien Fontaine-Vive

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© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name on 2 types of m-HfO2 substrate 2 types of metal Fabien Fontaine-Vive Matching surfaces: Small misfit for W bcc 110 oriented surface (3*a,1*b) on m-HfO2 001 surface (3*a, 1*b) Orthorhombic supercellMonoclinic supercell Supercell parameters: α=90 deg, β=99.25, γ=90 2 slabs of (3a,1b) m-HfO2 001 body centred cubic (bcc) W && hexagonal compact (hcp) Ti vacuum Supercell: α=90 deg, β=90, γ=90 a b c Monoclinic HfO2

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Relaxation engine: ab-initio (DFT) molecular dynamics combined with thermal annealing, 1-2 picosec for each deposition SIESTA code, LDA, Ceperley-Alder functional, Trouiller-Martins pseudopotentials, DZP orbitals Deposition of W atoms on m-HfO2 in orthorhombic supercell Fabien Fontaine-Vive Preferable positions for metal atoms (W & Ti): Hafnium sites Why ab-initio ? * Creation / rupture of bonds (ionic, covalent, hydrogen ….) => suitable for inorganic materials (but also for organic, bio….) * Parameter-free * Very powerful method to predict properties of crystalline systems

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© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Relaxing cell parameters of (W/HfO2) W hcp-like 110 on m-HfO2 001 W bcc 111 on ~ortho-mono HfO2 W hex-dia 110 on m-HfO2 001 W hex-dia 110 on m-HfO2 001 Phase transition No phase transition Fabien Fontaine-Vive

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© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Interfacial structures and energies of W/HfO2 4 types of construction, 4 types of relaxed interfaces (T=0K) 4ML W_hcp 110 / m-HfO monolayer W_hd + 3 ML W_bcc 110 / m-HfO ML W_hd 110 / m-HfO ML W_bcc 111 / ~o-mHfO2 001 Interfacial layer structure Octa (4W-O-2Hf) Tri (2Hf-O-1W) Tetra (2Hf-O-2W) Tri (2Hf-O-1W) ~Tetra (2Hf-O-2W) ~Tri (2Hf-O-1W) Tri~tetra (2Hf-O-1W) Tri (2Hf-O-1W) Formation energies of metal bulk structures (eV/atom) bcc = bcc+0.47bcc+0.77 Interfacial energies (eV) hd hd = hd Fabien Fontaine-Vive hd Stack energy (eV) bcc/o bcc/o+14.7 bcc/o+9.9 bcc/o+6.8 Surface energy of metal films (eV/atom) hcp 110=0.21hd 110=0.03bcc 111=0.16

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Interfacial structures and energies of Ti/HfO2 4ML Ti_hcp 110 / m-HfO ML Ti_hd 110 / m-HfO2 001 Interfacial layer structure Octa (4Ti-O-2Hf) Tri (2Hf-O-1Ti) Tetra (2Hf-O-2Ti) Tri (2Hf-O-1Ti) Formation energies of metal bulk structures (eV/atom) hcp+0.03 hcp = Interfacial energies (eV) hcp+3.66 hcp = Fabien Fontaine-Vive Stack energy (eV) hcp/m hcp/m+1.1 hcp=0.17hd=hcp Surface energy of metal films (eV/atom)

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Crystallographic compatibilities ? Fabien Fontaine-Vive Interfacial structure mHfO2 (001) / mHfO2 (001) Tetragonal (2Hf-O-2Hf) +Trigonal (2Hf-O-1Hf) Interfacial structure W / HfO2 (and Ti / mHfO2) W bcc 111 / o-mHfO2 W hd 110 / m-HfO2 001 W hcp 110 / m-HfO2 001 Octa (4W-O-2Hf) Tri (2Hf-O-1W) Tetra (2Hf-O-2W) Tri (2Hf-O-1W) ~Tetra (2Hf-O-2W) ~Tri (2Hf-O-1W) Fabien Fontaine-Vive a b Monoclinic HfO2 c

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Crystallographic compatibilities ? Fabien Fontaine-Vive WN hex 110 / mHfO2 001 W2N / mHfO2 Thermal annealing Without thermal annealing XRD Interfacial structure WNx / mHfO2 Interfacial structure mHfO2 (001) / mHfO2 (001) a b Monoclinic HfO2 c

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Valence Band Offset and metal work function Fabien Fontaine-Vive Band alignement method of Van de Walle & Martin + Many-body (GW) corrections (ABINIT code) VBO exp = 3.4 eV, (P+) VBO=4.0 eV (N+) VBO=3.5 eV (P+) Vacuum work function of metallic films (eV) 4ML W_hcp 110 / m-HfO monolayer W_hd +3 ML W_bcc 110 / m-HfO ML W_hd 110 / m-HfO ML W_bcc 111 / o-HfO2 001 Polymorphism (or/and poly-orientation! ) of the metallic films could explain the wide range of work functions Wf hcp 110= 4.1 For Titanium, Wf = 3.4 Wf hd 110=4.4 For Ti Wf = 4.1 Wf bcc 111 exp = 4.5 eV Wf bcc 110 exp = 5.2 Wf bcc on HfO2 exp= 5.0 (P+) W/HfO2 Wf bcc 110 calc = 5.1

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Electronic properties of W/HfO2 and Ti/HfO2 interfaces surface of isodensity at the Fermi level (HOMO density) Charge transfer at the metal/oxide interface due to evanescent metal wavefunctions in the oxide => creation of interfacial dipole W Ti HfO2 Fabien Fontaine-Vive

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Interface Ti / W / m-HfO2: stabilizing meta-stable phases ? Fabien Fontaine-Vive 2 ML Ti_hcp 4 ML W_hcp 2 ML m-HfO2 1 ML Ti_hcp + 1ML Ti_bcc 4 ML W_bcc 1 ML o-HfO2 Phase transition Natural phases, not natural phases 3 ML Ti_hcp 4 ML W_hcp 2 ML m-HfO2 1 ML Ti_hcp + 2ML Ti_bcc 3 ML W_bcc + 1ML W_hcp 2 ML m-HfO2 1 ML m-HfO2 Phase transition

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name These meta-stable phases exist in reality ? Fabien Fontaine-Vive Titanium metal at high pressure: Synchrotron experiments and ab initio calculations Rajeev Ahuja et al., PRB 2004 hcp -> (Temperature) ω -> bcc transition phase under pressure Growth of face-centred-cubic titanium on aluminium (fcc) S K Kim et al., J. Phys. Cond. Matt., 1996 For W, transition phase bcc -> double hcp at P > 6.5 Mbar Ruoff et al., PRB, 1998

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Substrate HfOx (O-rich), deposition of Ti atom Formation of TiO2 octahedral structure Fabien Fontaine-Vive

© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans lautorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Presentation name - Speaker name Metal-oxide interfaces = key-lock structure => ab-initio can design Ab-initio thermal annealing favors the apparition of meta-stable interfaces and relaxing cell dimensions favors the way back to the metal natural phase (depend on the thickness metal/oxide) Real interface with high-k oxide monoclinic HfO2 = -after the first atomic layer deposition => metal sites = Hafnium sites (=> ms-film in hexagonal structure, metal orientation determined by the oxide orientation) -structure of upper films determined by the deposition techniques -stability of interfacial films depend on the degree of incommensurability between metal and oxide. In W/HfO2, a possible coexistence of W bcc 111 (+1-2 monolayer of o-HfO2) and W bcc 110 (+m-HfO2) -MO electronic properties and interactions determined on 2 monolayers Conclusion on metal-oxide interfaces Fabien Fontaine-Vive