Status and Prospects for VUV Ellipsometry (applied to high-k and - - PowerPoint PPT Presentation

Status and Prospects for VUV Ellipsometry (applied to high-k and low-k materials)

N.V. Edwards

Advanced Products Research and Development Laboratory Semiconductor Products Sector, Motorola, Inc.

Requires invention/ potential showstopper Development required Solution known

Outline

1

Quick Introduction to Ellipsometry

• Why do we need the VUV?

2

VUV SE: Initial Challenges

• Instrumentation and analysis

3

Applications and Advantages of VUV SE

• Increased sensitivity to film thickness
• Increased access to unique spectral features

4

VUV SE of High- k Materials

• Thickness, bandgap, interface layer

5

VUV SE of Low -k Materials

• Porosity, low index inclusions

6

Conclusion

Introduction: What is ellipsometry? 1

• Traditional SE can be static or dynamic, 1770 to 190 nm

– In-line metrology (thickness, index) – Material diagnostics (band gap, alloy composition, strain) – Optical constants (index of refraction, dielectric constant) – Control/ monitoring of, e.g,

• Semiconductor growth
• Etching
• Deposition of proteins on semiconductors

Introduction: What is ellipsometry? 1

• Traditional SE can be static or dynamic, 1770 to 190 nm

– In-line metrology (thickness, index) – Material diagnostics (band gap, alloy composition, strain) – Optical constants (index of refraction, dielectric constant) – Control/ monitoring of, e.g,

• Semiconductor growth
• Etching
• Deposition of proteins on semiconductors

VUV: <190 nm or > 6.5 eV

Introduction: What is ellipsometry? 1

• Why do we need VUV?

– Lithography

• 157 nm
• EUV

– Front end processing

• Thin high k films

– Back end processing

• Porous low –k interlayer dielectrics

Potential applications for analyzing any “transparent” dielectric and wideband gap semiconductor

1

Introduction: What is ellipsometry?

Source

Sample

Entrance Optics Exit Optics Detector

ϕ χi χf

χf / χ i → ρ

1

Introduction

Real and imaginary part of dielectric function, ε = ε1 + i ε2

Photon Energy (eV) 2 4 6 8 10 Real(Dielectric Constant), ε1 Imag(Dielectric Constant), ε2 1.5 2.0 2.5 3.0 3.5 4.0 0.0 0.5 1.0 1.5 2.0 2.5 ε

1

ε

2

HfO2

ε1 ε2

Optical Constants

ρ

Index of refraction n, Extinction coefficient k, n = n + i k

W avelength (nm ) 300 600 900 1200 1500 1800 Index of refraction ’n’ Extinction Coefficient ‘K’ 1.6 2.0 2.4 2.8 0.20 0.40 0.60 n k

Al2O3

( ) ( )

      −       + =       +       + = 1 1 2 1 1 1 2 1

2 1 2 1

2 2 2 2 2 2 νε σ νε σ

ε ε

k n

2

Challenges: Instrumentation

Measurements made:

• in air (any transparent medium will do)
• with quartz optical elements

Quartz and air absorb below 190nm

2

Challenges: Instrumentation

The world’s first VUV ellipsometer at the BESSY-I synchrotron source but not quite appropriate for industrial use……..

Challenges: Instrumentation

2

Xenon→ Deuterium quartz → MgF2 Spectral Range: 131 to 1770nm

• r

0.7 to 9.5 eV Available A.O.I. = 20° to 80° Compensator for high accuracy measurements of transparent region

However, reducing data to optical constants still was not routine

2

Challenges: Data Reduction for VUV SE

Source

Sample

Entrance Optics Exit Optics Detector

ϕ χi χf

χ→ρ→ε

131 to 1770 nm

Experimental Data

Photon Energy (eV) 2 4 6 8 10 Ψ in degrees ∆ in degrees 20 40 60 80

• 100

100 200 300

Exp Ψ

• E 65°

Exp ∆-E 65°

Sample Properties: d, n, k, ε composition roughness bandgap porosity

Model

2

Challenges: Data Reduction

substrate εs ambient εa

      + −

+ =

ρ ρ ε

ϕ ϕ ϕ

1 1 tan sin sin

2 2 2 2 s

d ambient εa

• verlayer εo

substrate εs

} <ε>

( )( ) ( )

        − − − − + = ϕ λ π ε

ε ε ε ε ε ε ε ε ε ε ε sin

2 4 a s a s

• a
• s

s a id s

n

3-phase model: 2-phase model:

*

χi χf

2

Challenges : Data Reduction

*Information is returned over the penetration depth of light in the heterostructure

(penetration depth is a function of λ )

*Model assumes mathematically sharp interfaces

}

εs

• verlayer εo

substrate εs

*Must account for:

• Inorganic/ organic contamination
• Roughness
• Interface layers

}

Significant for VUV SE

• f high and low k

films

2

Challenges : Data Reduction

εs:

εs Substrate is foundational; Substrate = Si

Fitting up to DUV is routine; Si optical constants are well known: Aspnes, Herzinger Jellison, Yasuda

No optical constants for Si in VUV

Si

OSG

2

Challenges: Data Reduction

Can’t we just extrapolate optical constants?

Photon Energy (eV) 2 4 6 8 10 Reflection 0.20 0.30 0.40 0.50 0.60 0.70

Model Fit Exp pR 40°

Reflectivity data Model fit

Big problems

(with extrapolated optical constants)

No! Need to determine VUV optical constants for Si.

Si

OSG

Approach:

• 9 thermal oxide samples grown on Si,

from ~8 Å to 2200 Å thick

• multiple angle of incidence (45 to 75°)
• multi-sample analysis

2

Challenges: Data Reduction

• interface layer of 9.4 Å for

all samples

• fit parameters coupled in

interface and SiO2 layers, except for Amp, E1 offset

• could NOT fit data without

interface layer

Interface Layer

Si: Parameterized Semiconductor Layer SiO2: Tauc-Lorentz oscillator

Amp= 40.024, En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.263

Interface Layer: Tauc-Lorentz oscillator Amp= 158.67, En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.5705

• interface layer of 9.4 Å for

all samples

• fit parameters coupled in

interface and SiO2 layers, except for Amp, E1 offset

• could NOT fit data without

interface layer

Multi-Sample Analysis

2

Challenges: Data Reduction

Interface Layer

Si: Parameterized Semiconductor Layer SiO2: Tauc-Lorentz oscillator

Amp= 40.024, En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.263

Interface Layer: Tauc-Lorentz oscillator Amp= 158.67, En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.5705

• Fig. 1 a
• Fig. 1 b

Si Substrate

• Int. Layer 9.4 Å

SiO2 2189.3 Å Si Substrate

• Int. Layer 9.4 Å

SiO2 7.5 Å

Challenges: Data Reduction

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees ∆ in degrees

20 40 60 80 100

• 100

100 200 300 Photon Energy (eV) 2 4 6 8 10 <ε1> <ε2>

• 20
• 10

10 20 30 40 10 20 30 40

Data: ε1, blue ε2, green Model: red

SiO2/Si: Selected Fits from Multi-Sample Analysis Thinnest Sample:

2

Thickest Sample:

<ε1> <ε1> <ε2>

New CP: X1v-X1C transition

• 30
• 10

10 30 50 2 4 6 8 10

energy in eV pseudodielectric function

1.8 2.3 2.8 7.2 7.7 8.2

New Critical Point: X1v-X1C transition Motorola Aspnes Herzinger Jellison Yasuda X1V X1C

Si Optical Constants 2

Challenges: Data Reduction

Photon Energy (eV) 2 4 6 8 10 Index of refraction n 1.40 1.50 1.60 1.70 1.80 1.90 2.00

This work Palik, et al. Herzinger, et al.

Photon Energy (eV) 2 4 6 8 10 Extinction Coefficient k 0.000 0.010 0.020 0.030 0.040 0.050 0.060

2 SiO2 Optical Constants

Challenges: Data Reduction

Don’t extrapolate

• ptical constants!

Photon Energy (eV) 2 4 6 8 10 Index of refraction n 1.40 1.50 1.60 1.70 1.80 1.90 2.00

This work Palik, et al. Herzinger, et al.

Photon Energy (eV) 2 4 6 8 10 Extinction Coefficient k 0.000 0.010 0.020 0.030 0.040 0.050 0.060

2 SiO2 Optical Constants

Challenges: Data Reduction

Don’t extrapolate

• ptical constants!

S

• l

u t i

• n

k n

• w

n

3

Applications and Advantages of VUV SE

• 1. Optical Constants from VUV SE

Thickness[Å]

n and k from 131 to 1770 nm

W a v e l e n g t h [ n m ] R e f l e c t i v i t y [ % ]

Wavelength (nm) 300 600 900 1200 1500 1800 Index of refraction ' n' Extinction Coefficient ' k' 1.40 1.50 1.60 1.70 1.80 1.90 2.00 0.000 0.010 0.020 0.030 0.040 0.050 0.060

• 3. Achieved: ARC

design and experimental verification for improved contrast at desired inspection wavelengths

• 2. Reflectivity/

heterostructure design simulation Litho applications are numerous and obvious….

3

Applications and Advantages of VUV SE

• 30
• 10

Si SiO2

3

Applications and Advantages of VUV SE High- k Gates SiO2 SiON Metal oxides Low-k ILDs SiO2 TEOS OSGs

• 30
• 10

Si SiO2

• Increased sensitivity to film thickness
• Increased access to unique spectral features

4

VUV SE of High k Materials

2 4 6 8 10 10 20 30 40 50 60 70 Dielectric Constant Band Gap (eV)

SiO2 Al

2O 3

MgO CaO ZrSiO4 HfSiO4 Diamond Si

3N 4

SiC Si Y

2O 3

SrO ZrO2 HfO2 LaAlO3 La

2O 3

Ta

2O 5

BaO TiO2 SrTiO3

Band Gap and Dielectric Constant of Potential Gate Dielectrics

4

VUV SE of High k Materials

2 4 6 8 10 10 20 30 40 50 60 70 Dielectric Constant Band Gap (eV)

SiO2 Al

2O 3

MgO CaO ZrSiO4 HfSiO4 Diamond Si

3N 4

SiC Si Y

2O 3

SrO ZrO2 HfO2 LaAlO3 La

2O 3

Ta

2O 5

BaO TiO2 SrTiO3

Band Gap and Dielectric Constant of Potential Gate Dielectrics

0.1 0.2 0.3 0.4 0.5 100 150 200 250 300

~Equal Parts Si, N, O ~No Nitrogen

SiOxNy

Si: ~mid 30% O: ~high 40% N: ~high teens

Extinction Coefficient k Wavelength (nm)

Increased access to unique spectral features

4

(Very short term gate solution)

VUV SE of High k Materials: SiOxNy

0.1 0.2 0.3 0.4 0.5 100 150 200 250 300

~Equal Parts Si, N, O ~No Nitrogen

SiOxNy

Si: ~mid 30% O: ~high 40% N: ~high teens

Extinction Coefficient k Wavelength (nm)

Increased access to unique spectral features

4 Potential showstopper (633 nm metrology) Requires development (VUV SE)

VUV SE of High k Materials: SiOxNy

0.1 0.2 0.3 0.4 0.5 100 150 200 250 300

SiOxNy Extinction Coefficient k Wavelength (nm)

Increased access to unique spectral features

4

Photon Energy (eV) 2 4 6 8 10 Reflection 0.20 0.30 0.40 0.50 0.60 0.70

Model Fit Exp pR 40°

Reflectivity data Model fit

(with extrapolated optical constants)

VUV SE of High k Materials: SiOxNy

4

VUV SE of High k Materials

2 4 6 8 10 10 20 30 40 50 60 70 Dielectric Constant Band Gap (eV)

SiO2 Al

2O 3

MgO CaO ZrSiO4 HfSiO4 Diamond Si

3N 4

SiC Si Y

2O 3

SrO ZrO2 HfO2 LaAlO3 La

2O 3

Ta

2O 5

BaO TiO2 SrTiO3

Band Gap and Dielectric Constant of Potential Gate Dielectrics

4

VUV SE of High k Materials: bulk Al2O3

<ε1> 4.0 5.0 6.0 7.0

this work: model fit this work: data prior art: Yao, et al. J.Appl. Phys., 1999

Photon Energy (eV) 2 4 6 8 10 < ε2 > 1.0 2.0 3.0 4.0 3.0

• Gen. Osc. Model

1 mm rough surface 12.5 Å

c-plane Al2O3 substrate

4

VUV SE of High k Materials: bulk Al2O3

<ε1> 4.0 5.0 6.0 7.0

this work: model fit this work: data prior art: Yao, et al. J.Appl. Phys., 1999

Photon Energy (eV) 2 4 6 8 10 < ε2 > 1.0 2.0 3.0 4.0 3.0

• Gen. Osc. Model

1 mm rough surface 12.5 Å

c-plane Al2O3 substrate

O 2p nonbonding Mo

French, et al., J.Am. Ceram. Soc. 77[2] 412 (1994)

Wavelength (nm) 300 600 900 1200 1500 1800 Index of refraction ’n’ Extinction Coefficient ‘K’ 1.6 2.0 2.4 2.8 0.20 0.40 0.60 n k

Calculated from our model

4

VUV SE of High k Materials: bulk Al2O3

<ε1> 4.0 5.0 6.0 7.0

this work: model fit this work: data prior art: Yao, et al. J.Appl. Phys., 1999

Photon Energy (eV) 2 4 6 8 10 < ε2 > 1.0 2.0 3.0 4.0 3.0

Wavelength (nm) 300 600 900 1200 1500 1800 Index of refraction ’n’ Extinction Coefficient ‘K’ 1.6 2.0 2.4 2.8 0.20 0.40 0.60 n k

• Gen. Osc. Model

1 mm rough surface 12.5 Å

O 2p nonbonding Mo

c-plane Al2O3 substrate

Solution known

French, et al., J.Am. Ceram. Soc. 77[2] 412 (1994)

Calculated from our model

4

VUV SE of High k Materials

2 4 6 8 10 10 20 30 40 50 60 70 Dielectric Constant Band Gap (eV)

SiO2 Al

2O 3

MgO CaO ZrSiO4 HfSiO4 Diamond Si

3N 4

SiC Si Y

2O 3

SrO ZrO2 HfO2 LaAlO3 La

2O 3

Ta

2O 5

BaO TiO2 SrTiO3

Band Gap and Dielectric Constant of Potential Gate Dielectrics

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

Si Substrate 1 mm Interface Layer 2 Å Hafnia 207 Å Surface Roughness 9 Å

Phase: monoclinic Confirmed with XRD analysis, (Rich Gregory, PMCL)

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees ∆ in degrees

20 40 60 80 100

• 100

100 200 300

Model Fit Exp Ψ-E 65° Exp Ψ-E 70° Exp Ψ-E 75° Model Fit Exp ∆-E 65° Exp ∆-E 70° Exp ∆-E 75°

MSE= 1.6956

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 1.01 2 4 6 8 10 12 14 16 Interface Layer Thickness in Ang. Relative MSE

• fix parameter to be evaluated
• allow other parameters to vary
• calculate relative MSE
• repeat for next iteration

Si Substrate 1 mm Interface Layer 2 Å Hafnia 207 Å Surface Roughness 9 Å

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 1.01 2 4 6 8 10 12 14 16 Interface Layer Thickness in Ang. Relative MSE

Requires development

• fix parameter to be evaluated
• allow other parameters to vary
• calculate relative MSE
• repeat for next iteration

Si Substrate 1 mm Interface Layer 2 Å Hafnia 206.6 Å Surface Roughness 9 Å

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si Photon Energy (eV) 2 4 6 8 10 Real(Dielectric Constant), ε1 Imag(Dielectric Constant), ε2 2 4 6 8 10 2 4 6 8

ε1 ε2

Possible interpretation, after preliminary look at bandstructure (from Alex Demkov, PSRL) : Onset of absorption due to indirect gap. The onset from the model is 5.02 eV Direct transition direct Or, this could be an exciton before the bandedge (which would place the gap at 7 eV). We are investigating. Option 1: Option 2:

x

Bandgap for

• ption 2

1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 Energy in eV e1 1 2 3 4 5 6 7 2 4 6 8 10 Energy in eV e2

monoclinic amorphous monoclinic amorphous Real Part of the Dielectric Function vs. Energy Imaginary Part of the Dielectric Function vs. Energy

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

T1

No anneal Increasing anneal temp

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

• D. E. Aspnes, SPIE Vol. 452 (1983), p. 60.

2 4 6 8 2 4 6 8 10

Energy in eV ε 2

HfO2: Monoclinic Amorphous

• ellipsometric critical points will broaden & shift

in energy with changes in crystal structure

• sensitivity due to dependence of electronic

polarizabilities on the presence (or absence) of long-range order on the scale of 10 to 100Å

• ε =ε1 +iε2 →→ dipole moment per unit volume

→→ ellipsometry is a nondestructive means of determining densities of amorphous, poly, or microscopically inhomogeneous materials

Direct gap of Si shown, top. Higher lying optical transitions

• f wide bandgap materials are

similar, but at higher energies (VUV).

1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 Energy in eV e1 1 2 3 4 5 6 7 8 2 4 6 8 10 Energy in eV e2

Monoclinic; all others mixed phase (M + tetragonal) with increasing percentage of monoclinic phase with increasing anneal temp Real Part of the Dielectric Function vs. Energy Imaginary Part of the Dielectric Function vs. Energy

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

T2

No anneal Increasing anneal temp

2 4 6 8 10 12 2 4 6 8 10 energy in eV e1

Real Part of the Dielectric Function vs. Energy

1 2 3 4 5 6 7 8 2 4 6 8 10 Energy in eV e2

Imaginary Part of the Dielectric Function vs. Energy

4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

T3

No anneal Increasing anneal temp

Samples were mixed phase (T +M) as deposited and under all of the annealing conditions, except for the highest anneal temp, which was single phase monoclinic.

2 4 6 8 10 12 2 4 6 8 10 energy in eV e1

Real Part of the Dielectric Function vs. Energy

1 2 3 4 5 6 7 8 2 4 6 8 10 Energy in eV e2

Imaginary Part of the Dielectric Function vs. Energy No anneal Increasing anneal temp

Requires development (need a bulk film, for each phase to interpret data) 4

VUV SE of High k Materials: ‘thin’ hafnia films on Si

T3

Samples were mixed phase (T +M) as deposited and under all of the annealing conditions, except for the highest anneal temp, which was single phase monoclinic.

4

VUV SE of High k Materials: sensitivity to thickness Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80 100

Model Fit Data 65° Data 70° Data 75°

Si Substrate 185 Å Al2O3

4

VUV SE of High k Materials: sensitivity to thickness

1) Why do we have increased sensitivity for measuring thin films in the VUV? 2) Ellipsometry gives optical thickness nd. How do we separately determine n and d? Photon Energy (eV) 2 4 6 8 10

Ψin degrees

20 40 60 80 100

Model Fit Data 40° 45° 50° 55° 60° 65° 70° 75°

Si Substrate 985 Å SiO2

for 1 interference cycle:

Small values of d will occur for small values of λ

nd 2

2

− =

∆λ λ

E

hc nd ∆

= ∆ =

π

θ π

4

2

4

VUV SE of High k Materials: sensitivity to thickness

80

Ψin degrees

20 40 60

Model Fit Data 40° 45° 50° 55° 60° 65° 70° 75°

Si Substrate 95 Å SiO2 Photon Energy (eV) 2 4 6 8 10

Ψin degrees

20 40 60 80

Ψin degrees

20 40 60 80 Si Substrate 145 Å SiO2 Si Substrate 500 Å SiO2

4

VUV SE of High k Materials: sensitivity to thickness 10 20 30 40 50 2 4 6 8 10

energy in eV Psi 10 Ang 20 Ang 30 Ang 40 Ang 50 Ang 60 Ang

HfO2 Projected gate thickness 40-50Å

4

VUV SE of High k Materials: sensitivity to thickness 10 20 30 40 50 2 4 6 8 10

energy in eV Psi 10 Ang 20 Ang 30 Ang 40 Ang 50 Ang 60 Ang

HfO2 Potential showstopper (for 633 nm metrology and VUV SE post mortem diagnostics*) *Aspnes group is working on a solution

5

Low k Primer

Cu Low κ

Si

Thicknesses are greater, other problems exist

5

Low k Primer

400 440 480 520 560 5 6 7 8 9 10 1 1.2 1.4 1.6 1.8 2 2.2

Absorption (nm) Porosity (%) Hardness (GPa)

400 440 480 520 560 5 6 7 8 9 10 1 1.2 1.4 1.6 1.8 2 2.2 Absorption Onset (nm) Relative Porosity

Absorption (nm) Porosity (%) Hardness (GPa)

Production Research

Absorption Onset and Relative Porosity as a Function of Hardness

• Institution to institution
• Reactor to reactor
• For slight adjustments to process parameters…

nominally similar OSGs can be dramatically different

Why?

5

Low k Primer

Origin of OSG Porosity

Point of Growth Cavity

5

VUV SE of Low k Materials: sensitivity to density Recall that SE is sensitive to long range order on the scale of 10 to 100Å…

EMA Calculation of SiO2 n with increasing void fraction

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 500 1000 1500 2000

SiO2--0% 10% 20% 30% 40% 50% 60% 70% 80% 90% Air--100%

Increasing Porosity

n

λ

5

VUV SE of Low k Materials: sensitivity to density

0.0E+00 5.0E-06 1.0E-05 1.5E-05 2.0E-05 2.5E-05 3.0E-05 350 400 450 500 550

k wfr13 wfr14 wfr17 wfr18 wfr19 wfr20 wfr21 SiO2

1.405 1.415 1.425 1.435 1.445 1.455 500 700 900 1100

n

Optical Properties of OSG Films

wavelength in nm

Optical Properties of OSG Films

5

VUV SE of Low k Materials: sensitivity to density Optical Properties of OSG Films

0.0E+00 5.0E-06 1.0E-05 1.5E-05 2.0E-05 2.5E-05 3.0E-05 350 400 450 500 550

k wfr13 wfr14 wfr17 wfr18 wfr19 wfr20 wfr21 SiO2

1.405 1.415 1.425 1.435 1.445 1.455 500 700 900 1100

n

Optical Properties of OSG Films

wavelength in nm

n = n +ik

5

VUV SE of Low k Materials: sensitivity to density Optical Properties of OSG Films

0.0E+00 5.0E-06 1.0E-05 1.5E-05 2.0E-05 2.5E-05 3.0E-05 350 400 450 500 550

k wfr13 wfr14 wfr17 wfr18 wfr19 wfr20 wfr21 SiO2

1.405 1.415 1.425 1.435 1.445 1.455 500 700 900 1100

n

Optical Properties of OSG Films

wavelength in nm

n = n +ik

For porous SiO2, k should be 0 for whole spectral range….what is going on?

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80

Model Fit Exp E 65°

Why can’t OSG be treated like an

• xide?……………………...……………..….(or like a porous oxide?)

3% Porosity

Why can’t OSG be treated like an

• xide?……………………...…….(or like a porous oxide?)

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80

Model Fit Exp E 65°

5

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80

Tauc-Lorentz Model

VUV SE of Low k Materials

5

VUV SE of Low k Materials

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80

Tauc-Lorentz Model

5

VUV SE of Low k Materials

Photon Energy (eV) 2 4 6 8 10

Ψ in degrees

20 40 60 80

Model Fit Exp E 65°

← Cauchy / Urbach→ ← Sellmeier → Tauc-Lorentz Tauc-Lorentz + 2 Gaussians

500 1000 1500 2000 2500 3000

Frequency (cm-1)

Raman (blue) and absorbance (red) spectra of a SiCOH film (#13) on Si.

a-Si (film) c-Si LO (sub.) Si-O bend Si-O stretch Symmetric CH3 bend Si-H stretch

• Asymm. C-H stretch

C=O stretch c-Si 2LO (sub.) Si-O-Si stretch Si-CH3 bend Si-CH3 deform Si-C stretch Asymmetric CH3 bend

• Symm. C-H stretch

H-SiO3

2100 2200 2300

Frequency (cm-1)

H-SiO2

5

VUV SE of Low k Materials: low index inclusions complicate simple porosity measurements

Ran Liu, PMCL

0.0E+00 5.0E-06 1.0E-05 1.5E-05 2.0E-05 2.5E-05 3.0E-05 350 400 450 500 550

k wfr13 wfr14 wfr17 wfr18 wfr19 wfr20 wfr21 SiO2

1.405 1.415 1.425 1.435 1.445 1.455 500 700 900 1100

n

Optical Properties of OSG Films

wavelength in nm

200 400 600 800 1000 1200 1400

#13 #14 #18 #20

Raman Intensity Raman Shift (cm-1)

Wavelength (nm)

Comparison of the Raman spectra of several SiCOH films. Absorption edges of the SiCOH films from SE (b) and correlation between the absorption edge and the a-Si cluster concentration.

2.2 2.4 2.6 2.8 3 3.2 4.8 5 5.2 5.4 5.6 5.8 6 6.2

Absorption Edge (eV) R(480cm-1)/R(800cm-1)

(a) (b)

More a-Si

5

p simple porosity measurements

5

VUV SE of Low k Materials

Conclusions

• Samples with dramatically higher hardness had high RI values

» and thus higher electron densities/ lower relative porosities

• Films did not have the same optical properties as porous SiO2

across the spectral range measured

» the change in structure introduced by interstitial CHx is causing something more than a mere increase in porosity Raman, FTIR, XRR, EELS

5

VUV SE of Low k Materials

Some Advice…..

• DO NOT treat these films as oxides in in-line metrology recipes

without first confirming that they are not absorbing.

• DO NOT apply optical models outside of their range of

applicability, for either in-line or spectroscopic instruments.

The dramatic difference between the onset of absorption and onset

• f opacity in OSG films makes this very dangerous for those hoping

to extract film thickness or porosity from their optical measurements.

VUV SE: status and prospects…. High k Low k

Extract n and d independently for thickness required for process Extract n and d independently for thickness required for process Sensitive to density and surface roughness in ‘thick’, single layer films Sensitive to interface layer and surface roughness in ‘thick’, single layer films Sensitive to interface layer and surface roughness for multilayers Sensitive to pore size and distribution

Comparison to in-line metrology (633nm)….. High k Low k

Extract n and d independently for thickness required for process Extract n and d independently for thickness required for process Sensitive to density and surface roughness in ‘thick’, single layer films Sensitive to interface layer and surface roughness in ‘thick’, single layer films Sensitive to interface layer and surface roughness for multilayers Sensitive to pore size and distribution

Comparison to in-line metrology (633nm)…..

Extract n and d independently for thickness required for process Extract n and d independently for thickness required for process Sensitive to interface layer and surface roughness in ‘thick’, single layer films Sensitive to density and surface roughness in ‘thick’, single layer films Sensitive to interface layer and surface roughness for multilayers Sensitive to pore size and distribution

Propose dynamic SE measurements as the solution to shortcomings of VUV SE and traditional in-line metrology (it’s like a multi-sample analysis measurement, in time) High k Low k

Acknowledgements: Process and Materials Characterization Laboratory, PSRL, APRDL, JA Woollam Co.

TEM Bruce Xie Marti Erickson Joe Kulik Gordon Tam AFM Eppie Irwin Xiang-Dong Wang Raman and FTIR Ran Liu RBS Kevin Williamson Rich Gregory Crystal Growth Dina Triyoso Steve Smith Darrel Roan Kim Reid Kurt Junker Jason Vires SE Technical Assistance Stefan Zollner Craig Herzinger Tom Tiwald James Hilfiker