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

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

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

Resonant nuclear reactions p

UHV transfer system for growth and other analysis

Atomic Layer Deposition

Energy distribution for one angle 2D MEIS Data H+ Energy [keV] Angle 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)

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

SiO2/Si(001) oxidation (isotope marking) Transition zone, SiOx SiO2 Si (crystalline) Surface exchange Growth 800 C 900 C T (oC) Time (min) Oxide growth (Å) High-k 700 30 11 800 18 950 25 SiO2* 750 165 5 2640 10 900 60 300 21 1860 27 Faster interfacial SiO2 growth in case of high-k oxides in comparison to the SiO2 thickness growth for bare Si *Gusev, Lu, Gustafsson, Garfunkel, PRB 52 (1995) 1759.

Diffusion in gate dielectrics Si-substrate O-exchange in surface layer SiO2 growth at interface Oxygen (O2) transport in SiO2 O2 Si-substrate Atomic oxygen (O) transport in high-k films SiO2 growth, O-exchange at interface O-diffusion and exchange in bulk of oxide High-k O2 decomp. at surface O2 O 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

ZrO2 film re-oxidized in 18O2 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

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)) Sample as grown annealed in NH3 N content, 1015 cm-2 2.59 4.09

Gettering of O in the dielectric by Ti overlayer 300oC UHV Si (100) HfOx HfSiOx TiOx Ti RT Si (100) HfO2 SiO2 Si (100) HfO2.07 SiO2 27Å 6Å 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)

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 TiOx TiOd Si (100) HfO2 SiO2 Ti

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 Si (100) HfO1.9 HfSiOx TiOx x/2 SiO2 + Ti  x/2 Si + TiOx TiOx is Ti alloy overlayer DGo573K(x=0.49) = -54kJ/mol

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 HfO2 5Å InGaOx InGaAs(001) S

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

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 SrTiO3 78Å TiSixOy 2Å Si(001) 6Å SrO Ti1-xSrxSiyOz 8Å or