Material interactions of metal oxide dielectrics by dffhrtcv3

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									Ion Beam Analysis of the Composition and
        Structure of Thin Films


             Torgny Gustafsson, Physics
                        and
   Eric Garfunkel, Chemistry and Chemical Biology




                                                    1
                      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

                                                                                2
MEIS facility at Rutgers*
           NRP chamber    beam line


                                               ion implanter




                                      XPS system



                                      preparation
                                      chamber

                                      scattering
                                      chamber


 *Picture taken in 2004                                  3
Resonant nuclear reactions




                                a


                       15
             18
                  O         N
  p




                                    4
UHV transfer system for growth and other
                analysis




                                           5
Atomic Layer Deposition




                          6
                                     2D MEIS Data             SiO2/poly-Si/ZrO2/Ge(100)

                          Energy distribution
                            for one angle
H+ Energy [keV]




                          Angular distribution for
                          one element




                                                     Energy distributions:
                                                     • mass (isotope) specific
                  Angle                              • quantitative (2% accuracy)
                                                     • depth sensitive (at the sub-nm scale)
                                                                                           7
Energy spectrum and depth profiles




 Simulation of the peaks in the energy spectrum:
 l scattering cross section
 l stopping power (19 eV/Å in ZrO2)
 l energy straggling
 l detector resolution
 Þ "Near surface" depth resolution » 3 Å           8
         SiO2/Si(001) oxidation (isotope marking)
                             Surface
                             exchange


                             SiO2

                             Growth
                             Transition zone, SiOx
                                                                                                    900 °C

                             Si (crystalline)

           T (oC)   Time (min)      Oxide growth (Å)

            700        30                 11                                                        800 °C
            800        30                 18
High-k
            950        30                 25

                       165                 5
            750
                      2640                10
                                                       • Faster interfacial SiO2 growth in case of
SiO2*                  60                 10           high-k oxides in comparison to the SiO2
            900
                       300                21           thickness growth for bare Si
                      1860                27           *Gusev, Lu, Gustafsson, Garfunkel, PRB 52 (1995)   9
                                                       1759.
                 Diffusion in gate dielectrics
Oxygen (O2) transport in SiO2          Atomic oxygen (O) transport in high-k films
O-exchange                                              O-diffusion and    SiO2 growth,
                        SiO2
in surface                                 O2 decomp.   exchange in bulk   O-exchange
                        growth
 layer                                     at surface   of oxide           at interface
                        at interface




                Si-substrate                    O2         O       Si-substrate
    O2                                                  High-k

SiO2 films:                                  (Many) high-k films:
• amorphous after annealing                  • tend to crystallize at low T

• molecular O2 transport in SiO2             • atomic O transport in high-k film

• decomposition by SiO desorption            • high oxygen mobility
                                                                                          10
                                                        30Å Al2O3 annealed
                                                        in 3 Torr 18O2
                        ZrO2 film re-oxidized in 18O2




                            No change in Zr profile
      Deeper O and Si       Surface flat by AFM


  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
                                                                             11
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))




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


                                                                                      12
Gettering of O in the dielectric by Ti overlayer
                        Ti                          TiOx
HfO2.07 27Å           HfO2                         HfOx
                Ti                  300oC
 SiO2      6Å         SiO2                        HfSiO
                RT                   UHV
                                                  x
Si (100)             Si (100)                     Si (100)


                             •   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)


                                                                         13
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
                   Ti
                 HfO2           TiOd
                 SiO2
                Si (100)                                                14
Compositional profile after anneal to 300oC
                     • Ti + xO Þ 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


      TiOx         x/2 SiO2 + Ti ® x/2 Si + TiOx
     HfO1.9        TiOx is Ti alloy overlayer
     HfSiO         DGo573K(x=0.49) = -54kJ/mol
     x
     Si (100)                                                       15
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    S

  InGaAs(001)

                                                                  16
    Depth profiling for Al/HfO2/S-pass. InGaAs(001)

                             XPS results:

                                 AlOx
                                 HfO2       ?S      HfO2
                              a-InGaAsx           a-InGaAsx
                             InGaAs(001)         InGaAs(001)




              AlOx
              HfO2       s
S           a-InGaAsx
expected   InGaAs(001)
                                                               17
                            Interface composition
Normal incidence, 98keV H+, scattering angle 125o   Sr, Ti and O are observed in the
(substrate Si blocking)                             interface region - they are visible
SrTiO3/SrTiSixOy/Si(001)
                                                    to the ion beam (not blocked) in
                                                    this scattering geometry


                                                            SrTiO3           78Å

                                                            SrO              2Å
                                                            TiSixOy          6Å
                                                                  Si(001)

                                                                        or
                                                            SrTiO3           78Å

                                                            Ti1-xSrxSiyOz    8Å
                                                                  Si(001)


                                                                                      18

								
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