Electroless Capping and Diffusion Barriers For Copper ... Electroless Capping and Diffusion Barriers

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  • 11

    Electroless Capping and Diffusion Barriers

    For Copper Metallization Material properties

    Prof. Yosi Shacham Diamand ,

  • 22

    Co alloy barriersCo alloy barriers

    CoReP V. DUbin, 1993

    NiReP N. Petrov et al., 2001

    CoWP Y. Shacham, 1996

    CoWB- T. Osaka et al, 2002

    CoMoP Y. Shacham, 1999

    (Approximated date of 1st publication or patent )

  • 33

    Low solubility of Cu in Co and no phase formation, Cu solubility is about 0.1% at 400C P - Low solubility in Co -

    enrichment of grain boundaries? Affects microstructure, reducing grain size Froms amorphous structure at high concentration (> 12%)

    W: Low solubility in Co - Stuff the grain boundaries of the Cobalt

    Co - P

    Electroless Co alloys - Co(1-x-y) WxPy

    Negligible solid solubilitysolubility of P in fcc Co is less than 0.47 at. %Ishida and Nishizawa, Bull. Alloy Phase Diag. 11, 555 (1990)

    Negligible solid solubilitysolubility of W in fcc and E Co is less than 1 at. %

    Co - W

  • 44

    2. Electroless deposition of conformal ultra-thin Co1-x-yWxPy films

    Top FieldBottom Field / Sidewall

    Sidewall

    Comparison to current industrial technologyIonized Metal Plasma PVD

    Case study: Co0.9W0.02P0.08

    A. Kohn, M. Eizenberg,

    and Y. Shacham-Diamand,

    Appl. Surf. Sci., to be published

    BF CS TEM micrographs

  • 55

    400 600 800 1000 1200 140010-1

    100

    101

    T (oC)

    W s

    olub

    ility

    in fc

    c C

    o (a

    t. %

    )

    Sykes Magneli et al. Larikov et al. Takayama et al. (XRD) Takayama et al. (EPMA)

    400 600 800 1000 120010-2

    10-1

    100

    101

    T (oC)

    Cu

    solu

    bilit

    y (a

    t. %

    )

    Hasebe and Nishizawa Bruni and Christian Old and Haworth Hasebe and Nishizawa

    Proposed system for ULSI Cu metallization

    Cu: Low solubility in Co and no phase formation P, W: Low solubility in Co

    enrichment of grain boundaries? P: Affects microstructure, reducing grain size

    amorphous structure? W: Proposal

    introduction of a refractory alloying element may improve barrier efficiency?

    Co - P

    Co - W

    Co alloys - Co(1-x-y) WxPy

    Co - Cu

    Theoretical

    calculation

    Negligible solid solubilitysolubility of P in fcc Co is less than 0.47 at. %Ishida and Nishizawa, Bull. Alloy Phase Diag. 11, 555 (1990)

  • 66Nishizawa et al. , Bull. Alloy Phase Diag. 5, 161 (1984)

    Co - Cu

    The CoWP system for ULSI Cu metallization

    Nagender Naidu et al., Phase Diagrams of Binary Tungsten AlloysIndian Institute of Metals 60 (1991)

    Cu: Low solubility in Co and no phase formation P, W: Low solubility in Co

    enrichment of grain boundaries? P: Affects microstructure, reducing grain size

    amorphous structure? W: Proposal

    introduction of a refractory alloying element may improve barrier efficiency?

    Ishida et al. , Bull. Alloy Phase Diag. 11, 555 (1990)

    Co - P

    Co - W

    Co alloys - Co(1-x-y) WxPy

  • 77

    hcp Co

    fcc Co

    Orthorhombic Co2P

    0.4 0.6 0.8 1.0 1.2 1.4o

    Rad

    ial I

    nten

    sity

    (a.u

    .)

    600oC

    400oC

    as-dep

    s (A-1)

    Evolution of microstructure with thermal annealCo0.9W0.02P0.08

    Radial intensity of the SAEDas a function of the scattering vector

    0 5 10 150

    100

    200

    Num

    ber o

    f gra

    ins

    (-)

    Grain size (nm)

    0 5 10 15 200

    100

    200

    Num

    ber o

    f gra

    ins

    (-)

    Grain size (nm)

    0 40 80 1200

    100

    N

    umbe

    r of g

    rain

    s (-)

    Grain size (nm)

    Dark field plan view TEM micrographs, SAED, apparent grain size histograms

    as-dep

    400C

    600C

  • 88

    As-deposited structure:

    Hexagonal close-packed cobalt nanocrystallites (d ~ 3-5 nm), with a preferred basal plane orientation embedded in an amorphous Co(W,P) matrix.

    Evolution of structure with thermal anneal:

    T ~ 300C: hcp Co + amorphous Co(W,P) hcp Co ; Ea = 1.6 0.1 eV, constant nucleation rate, diffusion limited

    T ~ 420C: hcp Co hcp Co + orthorhombic Co2P ; Ea = 4.7 0.1 eV

    T > 500C: Delayed hcp Co fcc Co transformation relative to bulk Co

    P bonding shifts to covalent bonding at T > 600C

    Structure during failure of barrier:

    At T ~ 450C, the microstructure is hcp Co nanocrsytallites (d ~ 15 nm, 1 hour anneal), and small amounts of orthorhombic Co2P .

    Failure mechanism : grain boundaries diffusion

    Summary: Evolution of microstructure with thermal anneal

  • 99

    CoMoPCoMoP and and CoWPCoWP were deposited on sputtered seed were deposited on sputtered seed layers:layers:

    Ti/Cu or Ti/Co on Silicon oxide.Ti/Cu or Ti/Co on Silicon oxide.

    Ti improves the adhesion to the oxide.Ti improves the adhesion to the oxide.

    Cu or Co are the seed layer.Cu or Co are the seed layer.

    The samples were cleaned prior to the depositionThe samples were cleaned prior to the deposition

  • 1010

    Basic properties of Co(Mo,P)

    30 30 60 60 .cm.cm60 60 180 180 .cm.cmResistivityResistivity

    CoWPCoWPCoMoPCoMoP

    1. The resistivity depends on the composition, thickness and seed type

    2. Under similar conditions, e.g. same thickness, composition and seed type, the CoMoP layers has higher resistivity than CoWP

  • 1111

    Effect of Effect of CoWPCoWP and and CoMoPCoMoPcapping layers on Cu capping layers on Cu oxidation preventionoxidation prevention

  • 1212

    CoCo--MoMo--P P PourbaixPourbaix diagramdiagram

  • 1313

    CoCo--WW--P P PourbaixPourbaix diagramdiagram

  • 1414

    CoWPCoWP and and CoMoPCoMoP basic deposition Solutionbasic deposition Solution

    Ingredient Role Concentration

    CoSO47H2O Cobalt source 23 gr/l HB3O3 Buffer 31 gr/l

    3Na-citrate Cobalt complexing 130 gr/l

    NaH2PO2 Reducing agent and Phosphor source 21 gr/l

    RE610 Surfactant gr/l 0.05

    KOH pH set 8.9-9

    Na2MoO4 Mo source gr/l 0.1

    Na2WO4 W source gr/l 10

  • 1515

    CoMoPCoMoP and and CoWPCoWP basic propertiesbasic properties

    Properties CoMoP CoWP Mixed

    potential -789 mV 702mV

    Resistively 60-180 cm 48 cm

  • 1616

    XRD resultsXRD results

    CoMoPCoMoP CoWPCoWP

    Alfa-Co (111)

  • 1717

    CoMoPCoMoP and and CoWPCoWP as as oxidation protection oxidation protection

    layerlayer

  • 1818

    Experiment procedureExperiment procedure

    SandwichSandwich samples of Cu between barrier layers samples of Cu between barrier layers

    on SiOon SiO22 were made and subjected to oxidation were made and subjected to oxidation

    condition by heating in open air furnace.condition by heating in open air furnace.

    Surface resistance measurement were taken by Surface resistance measurement were taken by

    4pp during the process.4pp during the process.

    XPS profiling and spectrum was used to see the XPS profiling and spectrum was used to see the

    the changes in profile and Cu oxidation state.the changes in profile and Cu oxidation state.

  • 1919

    Heat treatmentHeat treatment

    For #1,#6 and 7#:For #1,#6 and 7#:300 min at 200C.300 min at 200C.170 min at 300C.170 min at 300C.200 min at 350C.200 min at 350C.

    For #8:For #8:300 min at 200C.300 min at 200C.60 min at 300C.60 min at 300C.

  • 2020

    Surface resistance measurementSurface resistance measurement

    R/Ro Vs Oxidation time

    0

    0.5

    1

    1.5

    2

    2.5

    3

    3.5

    0 200 400 600 800

    Time (min)

    R/R

    o

    CoMoP/Cu/CoMoPon Co seadCoWP/Cu/CoWP onCo seadCoWP/Cu/CoWP onCu seadCoMoP/Cu on Cusead

  • 2121

    1# 1# --XPS profile before treatmentXPS profile before treatment

  • 2222

    1# 1# --XPS profile after 110 min at XPS profile after 110 min at 350C350C

  • 2323

    1#1# -- Cu spectrum after 110 min at Cu spectrum after 110 min at 350C350C

  • 2424

    1# 1# --XPS profile end of experimentXPS profile end of experiment

  • 2525

    1# 1# -- Cu spectrum at the end of Cu spectrum at the end of experimentexperiment

  • 2626

    1# 1# -- Cu spectrum at the end of Cu spectrum at the end of experimentexperiment

  • 2727

    DiscussionDiscussionThe The CoWPCoWP and and CoMoPCoMoP oxidizing protection properties are oxidizing protection properties are close, with small advantage for close, with small advantage for CoMoPCoMoP..It seems that Co diffusion to the surface controls the barrier It seems that Co diffusion to the surface controls the barrier layer oxidizing leading to barrier splitting to oxidized Co and layer oxidizing leading to barrier splitting to oxidized Co and Co depleted layers. Co depleted layers. Until the oxidizing of the barrier is well advanced, the barrierUntil the oxidizing of the barrier is well advanced, the barriercontinues to defend the Cu from oxidizing.continues to defend the Cu from oxidizing.Barrier advanced oxidizing leads to itBarrier advanced oxidizing leads to its failure as barrier and s failure as barrier and Cu diffuse to the surface.Cu diffuse to the surface.

  • 2828

    CoMoPCoMoP and and CoWPCoWP -- Cu Cu diffusion barrierdiffusion barrier

  • 2929

    Experiment procedureExperiment procedure

    SandwichSandwich samples of Cu between samples of Cu between

    barrier layers on SiObarrier layers on SiO22 were made and were made and

    subj