Ellipsometry Porosimetry for Ultra Low K Material - Ellipsometry Porosimetry for Ultra Low K...

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Transcript of Ellipsometry Porosimetry for Ultra Low K Material - Ellipsometry Porosimetry for Ultra Low K...

  • 1

    Ellipsometry Porosimetry for Ultra Low K Material

    Dr Dorian ZAHORSKI

    SOPRA

    www.sopra-sa.com

    UCLA July 2006

  • 2

    Excellent dielectric properties of SiO2 have been the cornerstone for microelectronic revolution during the past 30 years.

    ⎟ ⎟

    ⎜ ⎜

    ⎛ += 2

    2 2 242 T

    L P L

    okRC ερ

    Better Interconnects require:

    1. Metals with low resistivity (Cu) 2. Dielectrics with low dielectric

    constant (low-k)

    Technology challenge: reduce RC delay

    ρ - metal resistivity k - relative dielectric constant L - line length P - metal pitch T - metal/dielectric thickness

    ULK characterization with EP

    Introduction of porous low K materials

  • 3

    ULK characterization with EP

    Adrien Darragon - Product Manager, SOPRA – sales@sopra-sa.com

    •EP is a unique technology to characterize CVD and spin coated porous ultra low K.

    •EP measures the change of the optical properties and thickness of the materials during adsorption and desorbtion of an organic solvent.

    •The analysis gives: •porosity of the Low K •pore size distribution •Average pore size •For both microporous and mesoporous, cumulative surface area, pore interconnectivity, Young modulus, thickness and refractive index.

    •EP qualifies the sealing layer of both patterned and blanket wafers.

    + solvant

    Porous material

  • 4

    Outline

    1. Principle and measurement setup 2. Porosity and Pore size measurements

    • Mesoporous • Microporous

    3. Young modulus 4. Pore killers and sealing

    • Blanket wafers • Patterned wafers • Interconnectivity

  • 5

    Porosity measurement

    From the thickness and refractive index measurements on the basis of Lorentz- Lorenz equation:

    From adsorption/desorption isotherms : Porosity pore interconnectivity

    no need to know the dense skeleton material properties

  • 6

    ELLIPSOMETRY is a method based on measurement of the change of the polarisation state of light after reflection at non normal incidence on the surface to study.

    Substrate (ns, ks)

    Thin Film 1 (n1, k1, T1) Thin Film 2 (n2, k2, T2)

    Ambient (n0, k0)

    foES

    Ei EP

    rs

    rp

    Er

    linear polarisation

    Ei n

    Ep Es

    Eout=r Ein Ep rpEs rs

    elliptical polarisation

    Eout=r Ein = (TanY eiDelta) Ein Ellipsometry measures TanY and Cos D

    Principle of Spectroscopic Ellipsometry

  • 7

    Experimental Measurement =

    Model Simulation ?

    No, proposition for new parameters

    Yes

    Cos D

    TanY

    Experimental Measurement Physical Model With an estimated sample structure

    - Film Stack and structure - Material n, k, dispersion - Composition Fraction of Mixture

    Cos D

    TanY

    Calculated values

    Film structure and optical properties proposed are correct.

    Advanced minimization algorithms

    for quick convergence

    Physical parameters n,k Thickness

  • 8

    Porosity measurement

    nre: refractive index measured when pores are empty nrl: refractive index measured when pores are filled nads: refractive index of the solvent

    Lorentz-Lorenz equations

  • 9

    Porosity measurement

    No need to know the refractive index of the skeleton V is the volume of open pores

    nre: refractive index measured when pores are empty nrl: refractive index measured when pores are filled nads: refractive index of the solvent

  • 10

    Measurement principle

    Acquisition of SE spectra

    Analysis of SE spectra: Calculation of Thickness / Refractive index

    0.0 0.2 0.4 0.6 0.8 1.0 0.393

    0.394

    0.395

    0.396

    0.397

    0.398

    0.399

    0.400

    0.401

    Chemnitz LK3 SOPRA

    Th ic

    kn es

    s, µ

    m

    Relative IPA Pressure

    Ads. Des.

    0.0 0.2 0.4 0.6 0.8 1.0

    1.30

    1.32

    1.34

    1.36

    1.38

    1.40

    1.42

    1.44

    Chemnitz LK3 SOPRA

    R ef

    ra ct

    iv e

    In de

    x

    Relative IPA Pressure

    Ads. Des.

    P/Po=1

    (P/Po) (P/Po)

    time

    Pr es

    su re

    Thickness vs partial pressure Refractive index @ 633nm vs partial pressure

  • 11

    Measurement principle

    0.0 0.2 0.4 0.6 0.8 1.0 0.393

    0.394

    0.395

    0.396

    0.397

    0.398

    0.399

    0.400

    0.401

    Th ic

    kn es

    s, µ

    m

    Relative solvent Pressure

    B E

    0.0 0.2 0.4 0.6 0.8 1.0

    1.30

    1.32

    1.34

    1.36

    1.38

    1.40

    1.42

    1.44

    R ef

    ra ct

    iv e

    In de

    x

    Relative solvent Pressure

    C F

    Lorentz-Lorentz Equations => Solvent volume vs rel.pressure

    0.0 0.2 0.4 0.6 0.8 1.0 0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    0.35

    So lv

    en t V

    ol um

    e

    Relative Solvent Pressure

    B D

    Porosity = 31%

  • 12

    From pores volume to PSD Meso Pores: Kelvin Pore size with diameter form 2 to 50nm(IUPAC classification) The solvent is in a liquid phase Po : equibrium vapor pressureP/Po: relative equilibrium vapor

    pressure above meniscus g : Surface tension of adsorptive VL : molar volume of adsorptive rk : mean radius of curvature q : wetting angle

    )/ln( 2

    0PPRT Vr Lγ=:radiusPore

    EP gives a distribution of pores for every relative pressure not a distribution a posteriori.

    0.0 0.2 0.4 0.6 0.8 1.0 0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    0.35

    S ol

    ve nt

    V ol

    um e

    Relative Solvent Pressure

    B D

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    0.1 1.0 10.0 Pore Radius (nm)

    dV /d

    (ln R

    )

    Ads Des Micro Ads Micro Des TOLUENE

    )01

    1 1 /ln(.

    2 PPRT

    Vr γ=

    )0/ln(. 2

    PPRT Vr

    n

    n n

    γ=

    )00/ln(. 2

    PPRT Vr Lγ=

  • 13

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    0.1 1.0 10.0 Pore Radius (nm)

    dV /d

    (ln R

    )

    Ads Des Micro Ads Micro Des TOLUENE

    Mesoporous material

    0.0 0.2 0.4 0.6 0.8 1.0 0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    0.35

    So lv

    en t V

    ol um

    e

    Relative solvent Pressure

    B D

    Kelvin

    Kelvin

    From Solvent volume to Pore Size Distribution : Hysteresis in the isotherms=> mesoporous material (r >1nm)

  • 14

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    0.1 1.0 10.0 Pore Radius (nm)

    dV /d

    (ln R

    )

    Ads Des Micro Ads Micro Des TOLUENE

    Mesoporous material

    Kelvin

    The pore radius for the adsorption is 2.5nm (cavities) and the pore radius for desorption is 1.9nm (connections)

  • 15

    0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    0.0 0.2 0.4 0.6 0.8 1.0

    Relative Pressure of Solvent

    So lv

    en t v

    ol um

    e

    Ads

    Des

    TOLUENE

    0.09

    Microporous material Micro pores: Dubinin Radushkevich Pore size with diameter below 2nm (IUPAC classification) The solvent is in a gaz phase

    [ ]{ }22 )/()/ln(exp/ OO EPPRTWoW β−= W/Wo: fractional filling of the micropore volume: Wo β: scaling factor (affinity coeff.) Eo: characteristic energy r: pore radius, nm, normal Distribution, average radius

    Pore radius: r = 6/Eo

    Microporous total volume : 20.5% Microporous percentage : 73% Microporous average radius : 0.62nm

    Ln(V) Ln²(p0/p) -6.36838614267765 60.965412465549 -4.67839007262632 49.221408284231 -5.16160802779383 41.3724559950233 -5.21082991099096 34.9376351838247 -4.12715216177882 26.8730040292041 -4.06884111672946 22.37662106353 -3.63299473960852 17.2037913967749 -3.05876043728472 11.4797802777917 -2.76752532211873 6.90585739520692 -2.56657315455311 4.17480130899704

  • 16

    0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    0.0 0.2 0.4 0.6 0.8 1.0

    Relative Pressure of Solvent

    So lv

    en t v

    ol um

    e

    Ads

    Des

    TOLUENE

    Solvent Volume / P/P0

    Microporous material

    0.09

    0.0

    0.1

    0.1

    0.2

    0.2

    0.3

    0.3

    0.4

    0.4

    0.5

    0.5

    0.1 1.0 10.0 Pore Radius (nm)

    dV /d

    (ln R

    )

    Ads Des Micro Ads Micro Des TOLUENE

    Mesoporous volume: 3.5%

    Microporous volume: 20% Pore size: 0.75nm

    Mesoporous distribution calculated with kelvin equation

    • Total Porous Volume: microporous volume mesoporous volume

    • Average pore size • Pore size distribution