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Ion Beam Analysis of the Composition and Structure of Thin Films

This article discusses medium energy ion scattering (MEIS) as a quantitative technique for analyzing the composition and structure of thin films. MEIS provides depth-sensitive, mass-specific, and quantitative information about the film's composition and depth profiles. The experimental details of the MEIS facility at Rutgers University, along with examples of energy distributions and depth profiles, are also provided.

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Ion Beam Analysis of the Composition and Structure of Thin Films

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  1. Ion Beam Analysis of the Composition and Structure of Thin Films Torgny Gustafsson, Physics and Eric Garfunkel, Chemistry and Chemical Biology

  2. Experimental Details • Medium Energy Ion Scattering: A refinement of Rutherford Backscattering Spectroscopy with enhanced depth and angle resolution (~3Å vs. ~100Å) • A quantitative technique, with well known cross sections and an unusually short distance between data and interpretation • MEIS counts the number of atoms in the sample • By analyzing peak shapes (energy distributions), depth profiles can be obtained

  3. MEIS facility at Rutgers* NRP chamber beam line ion implanter XPS system preparation chamber scattering chamber *Picture taken in 2004

  4. Resonant nuclear reactions a 18O 15N p

  5. UHV transfer system for growth and other analysis

  6. Atomic Layer Deposition

  7. H+ Energy [keV] Angle 2D MEIS Data SiO2/poly-Si/ZrO2/Ge(100) Energy distribution for one angle Angular distribution for one element Energy distributions: • mass (isotope) specific • quantitative (2% accuracy) • depth sensitive (at the sub-nm scale)

  8. Energy spectrum and depth profiles Simulation of the peaks in the energy spectrum: scattering cross section stopping power (19 eV/Å in ZrO2) energy straggling detector resolution "Near surface" depth resolution  3 Å

  9. Surface exchange Transition zone, SiOx SiO2 900 C Growth 800 C Si (crystalline) SiO2/Si(001) oxidation (isotope marking) • Faster interfacial SiO2 growth in case of high-k oxides in comparison to the SiO2 thickness growth for bare Si *Gusev, Lu, Gustafsson, Garfunkel, PRB52 (1995) 1759.

  10. Atomic oxygen (O) transport in high-k films Oxygen (O2) transport in SiO2 SiO2 growth, O-exchange at interface O-exchange in surface layer O-diffusion and exchange in bulk of oxide SiO2 growth at interface O2 decomp. at surface Si-substrate Si-substrate O2 O O2 High-k Diffusion in gate dielectrics • SiO2 films: • amorphous after annealing • molecular O2 transport in SiO2 • decomposition by SiO desorption • (Many) high-k films: • tend to crystallize at low T • atomic O transport in high-k film • high oxygen mobility

  11. 30Å Al2O3 annealed in 3 Torr 18O2 ZrO2 film re-oxidized in 18O2 No change in Zr profile Surface flat by AFM Deeper O and Si Isotopic profiling of Zr and Al oxides • Significant interfacial SiO2 growth for ZrO2, less for Al2O3 • Dramatic oxygen exchange: 18O replaces 16O • SiO2 growth rate faster than DG-like growth

  12. Presence of nitrogen in high-k film: effects on oxygen exchange • (HfO2)2(SiO2)/SiN/Si(001) films have been submitted to various post growth anneals (NH3, N2, O2, Tanneal =500-700oC) • only annealing in NH3/700oC/60s results in nitrogen incorporation in HfSiO6 with oxygen removal (final composition of HfSiO5N (O : N = 5:1))

  13. HfO2.07 Ti 27Å TiOx SiO2 6Å HfO2 HfOx Si (100) SiO2 300oC UHV Ti RT HfSiOx Si (100) Si (100) Gettering of O in the dielectric by Ti overlayer As-deposited amorphous HfO2 film has small amount of interfacial SiO2 (~6-7Å) and excess of oxygen (~HfO2.07) Deposited Ti forms uniform layer, no strong intermixing with HfO2; Oxygen concentration in Ti layer is small (TiOx, x<0.10)

  14. Ti HfO2 SiO2 Si (100) TiOx TiOd Composition of Ti/HfO2/SiO2/Si(001) gate stack(as-deposited) • Ti layer oxidizes on the surface and at the Ti/HfO2 interface (TiOx, x<1) • partial depletion of oxygen from HfO2 layer • HfO2 + Ti  HfO2-x + VO (HfO2)+ TiOx • SiO2 remains at the HfO2/Si(001) interface

  15. TiOx HfO1.9 HfSiOx Si (100) Compositional profile after anneal to 300oC • Ti + xO  TiOx • Decrease of the Si surface peak and decrease of the width of the O peak indicate partial removal of SiO2 layer • Incorporation of some of the Si initially present in the interfacial SiO2 layer in the high-k layer • After air exposure Ti oxidation in the surface layer x/2 SiO2 + Ti  x/2 Si + TiOx TiOx is Ti alloy overlayer DGo573K(x=0.49) = -54kJ/mol

  16. HfO2 5Å InGaOx InGaAs(001) HfO2 deposition on S-passivated InGaAs(001) • Sulfur (1.3×1015atms/cm2) is distributed at the HfO2/InGaAs interface • HfO2 layer has small oxygen excess; • Thin Ga-rich interfacial In0.13Ga0.87Ox:S layer is present, • Elemental As can still present at the interface at small concentration S

  17. XPS results: AlOx S ? HfO2 HfO2 a-InGaAsx a-InGaAsx InGaAs(001) InGaAs(001) s AlOx HfO2 S expected a-InGaAsx InGaAs(001) Depth profiling for Al/HfO2/S-pass. InGaAs(001)

  18. SrTiO3 78Å SrO 2Å TiSixOy 6Å or SrTiO3 78Å Ti1-xSrxSiyOz 8Å Si(001) Si(001) Interface composition Normal incidence, 98keV H+, scattering angle 125o (substrate Si blocking) SrTiO3/SrTiSixOy/Si(001) Sr, Ti and O are observed in the interface region - they are visible to the ion beam (not blocked) in this scattering geometry

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