Elliott, SD

Kessels, E

Leick, N

Potts, SE

Zydor, A

English

UCL Discovery

Plasma-Enhanced ALD of TiO2 using Cp-Based Precursors:Experiments and DFT CalculationsStephen E. Potts, Noémi Leick and Erwin KesselsEindhoven University of Technology, The NetherlandsAleksandra Zydor and Simon D. ElliottTyndall National Institute, IrelandALD 2011, Cambridge, MA, USA, 28th June 20111/ Applied Physics / S. E. PottsMotivationMixed (ternary) oxides• SrTiO3 and BaSrTiO3• Ultra-high-k dielectric.• Ti-Cp precursors are stable alternatives.• TiO2 ALD is “complex”.Better understanding of the plasma-enhanced ALD of TiO2• Plasma step: How do different plasma compositions affect growth?• Precursor step:Can DFT calculations help us understand growth?S. E. Potts et al., J. Electrochem. Soc., 157, P66 (2010) and referen es therein.2/ Applied Physics / S. E. PottsOutline• Motivation• Plasma-Enhanced ALD using Cp-Based Precursors• Ti(Cp*)(OMe)3 (A) and Ti(CpMe)(NMe2)3 (B)• O2, N2O and N2-O2 plasmas• DFT Calculations • Reactions of A, B and Ti(OMe)4 with hydroxylated TiO2• Hydrogen-bonding to surface sites• Towards the elimination of by-products• Conclusions3/ Applied Physics / S. E. PottsExperimental Details: ALDAtomic Layer Deposition• Remote ICP plasma• 200 W RF power• O2, N2O, N2/O2 (4:1)• 100 mm n-type Si(100) with native oxideOxford Instruments FlexALTM reactorA BDiagnostics• Spectroscopic ellipsometry• Rutherford backscattering spectrometryTiMeO OMeOMeMeMeMeMe Me TiMe2N NMe2NMe2Me4/ Applied Physics / S. E. PottsPlasma-Enhanced ALD of TiO2• Two similar precursors in the same reactor with Ti(OiPr)4 as a reference.• B deposited more Ti atoms/cycle.• B shows signs of thermal activation.• Nitrogen in B a cause of this?• Presence of N in the plasma?• Decomposition?100 150 200 250 300 350 4000.000.020.040.060.080.100.12 nm/cycle100 150 200 250 300 350 4000.00.51.01.52.02.53.0  ×1014  atoms/cm2 /cycle100 150 200 250 300 350 4002.02.53.03.54.04.5 Mass DensityTi Atoms Deposited  g/cm3Deposition Temperature (°C)Ref.  Ti(OiPr)4A  Ti(Cp*)(OMe)3B  Ti(CpMe)(NMe2)3Growth per Cycle[A + Ref.] S. E. Potts et al. at the ALD Conference, Seoul, 2010.[B] A. Sarkar et al., ECS Trans., 33, 385 (2010).A BOiPrTiiPrO OiPrOiPr TiMeO OMeOMeMeMeMeMe Me TiMe2N NMe2NMe2MeRef.5/ Applied Physics / S. E. Potts0 10 20 30 40 50 60 70 80 90 1000.00.51.01.52.02.53.03.54.04.50.038 nm/cycle0.032 nm/cycle   Thickness (nm) O2 plasma N2-O2 plasma N2O plasma0.036 nm/cycle0 10 20 30 40 50 60 70 80 90 1000.00.51.01.52.02.53.03.54.04.55.05.50.046 nm/cycle0.049 nm/cycle  Thickness (nm)ALD Cycles0.047 nm/cycle• Addition of N2 to an ozone generator can have a significant effect on growth.A. Delabie et al., Electrochem. Solid-State Lett., 13, H176 (2010).• All growths per cycle are the same, within experimental error.• Independent of the plasma gas composition.Addition of N2 to the O2 PlasmaAB350 °C200 °CA BTiMeO OMeOMeMeMeMeMe Me TiMe2N NMe2NMe2Me6/ Applied Physics / S. E. PottsExperimental Details: DFT CalculationsG. Kresse and J. Furthmüller, Comput. Mater. Sci., 6, 15 (1996).• Periodic plane wave density functional theory (DFT), • VASP package,• For the surface model, 1 × 2 × 1 k-point sampling grids were used for the (4 × 2) surface expansions,• Core-valence interaction treated using projector augmented wave (PAW) gradient-corrected density functional PBE, • Plane-wave basis <396 eV, • The molecular geometries of the precursor molecules, Ti(OMe)4, A, B, Cp*H, MeOH, HNMe2 and water were individually relaxed in a box of dimensions 20 × 20 × 20 Å, with a 396 eV cutoff energy and Γ-point sampling.• Comparison of A and B with Ti(OMe)4• Surface• Rutile (110)• Water molecules bound to rutile surface• Eads = -0.79 eV per water molecule7/ Applied Physics / S. E. PottsInitial Reaction: Hydrogen BondingTi H C O NTi(Cp*)(OMe)3 Ti(OMe)4 Ti(CpMe)(NMe2)3Eads = -0.48 eVEads = -0.35 eV Eads = -0.70 eVPrior to full ligand exchange> >• H-bonding favourable for all precursors.• Stronger bonding than expected.• B most likely to H-bond: quantum mechanics show instantaneous proton transfer.A B8/ Applied Physics / S. E. PottsEnergy of AdsorptionTowards elimination of MeOH or HNMe2Eads = -0.62 eVEads = +0.79 eVunfavourableEads = +0.11 eVunfavourableTi(Cp*)(OMe)3 Ti(OMe)4• Formation of Ti–O bond and ligand loss for A and B unfavourable.• Cp compounds sterically crowded would not expect ALD growth.• Ti(OMe)4 has room to rotate  allows for a full reaction.Ti(CpMe)(NMe2)3A BTi H C O N9/ Applied Physics / S. E. PottsTiMe2NNNMe2MeTiMe2NNNMe2MeTiMe2NNCH2Me CH2HMeMe CH2H- HNMe2MeExample Decomposition of Precursor BOne of many possibilities…Reactant Transition State ProductEa = +130 kJ/mol(+1.35 eV/molecule)∆E = (Eproducts-Ereactant) = +126 kJ/mol(+1.31 eV/molecule)• Endothermic overall, so thermodynamically unlikely.• Less coordinative saturation – “opens up” metal centre.Ti H C O N10/ Applied Physics / S. E. PottsEnergy of Adsorption: Decomposition ProductTowards elimination of HNMe2Eads = -1.25 eV• Full adsorption favoured for decomposition product of B.• Less-crowded ligand coordination sphere.Ti(CpMe)(NMe2)(CH2NMe) Ti(CpMe)(NMe2)3Ti H C O NEads = +0.11 eVB“B”decompositionproduct11/ Applied Physics / S. E. PottsAddition of N2 to an O2 plasma• No significant effect on the growth per cycle of TiO2 from A and B.ConclusionsDFT calculations of Ti-Cp compounds• Very crowded ligand sphere• Elimination of by-products not favourable• Cannot do more than H-bond• Possible decomposition of Baffords a more-reactive species. More Ti atoms/cycle. 100 150 200 250 300 350 4000.00.51.01.52.02.53.0Ref.  Ti(OiPr)4A  Ti(Cp*)(OMe)3B  Ti(CpMe)(NMe2)3  ×1014  atoms/cm2 /cycleDeposition Temperature (°C)Ti Atoms DepositedA12/ Applied Physics / S. E. Potts13/ Applied Physics / S. E. PottsEads = +0.60 eV Eads = +0.37 eVAdsorption via Cp* for Precursor A?• Endothermic overall, thermodynamically unlikely.• Cannot occur via H-bonding.• Cp* not basic enough to undergo an acid-base reaction under these conditions.Ti H C O N

Plasma-Enhanced ALD of TiO₂ using Cp-Based Precursors: Experiments and DFT Calculations

https://discovery.ucl.ac.uk/10114898/1/SEPotts_ALD2011.pdf

Plasma-Enhanced ALD of TiO₂ using Cp-Based Precursors: Experiments and DFT Calculations

Abstract

Similar works

Full text

Available Versions

UCL Discovery