1. Funding Source: NSF (DMR-1104934)
Infrared Optical Conductivity of Ni1-xPtx alloys and Ni1-xPtxSi Monosilicides
Lina S. Abdallah, Travis I. Willett-Gies, Eric DeLong, S. Zollner, New Mexico State University, Las Cruces, NM Harland G. Tompkins, J.A. Woollam Co. (consultant) C. Lavoie, A. S. Ozcan, IBM M. Raymond, GLOBALFOUNDRIES
Funding Source: NSF (DMR )

2. Infrared Ellipsometry
Bulk sample
interferometer (λ)
polarizer
analyzer
detector Φ
Spectral range: 250 – 8000 cm-1 (0.125 – 40 μm)
P plane
S plane
P plane
Optical conductivity

3. Lorentz Model: Oscillating Field
Classical harmonic oscillator
Equation Of Motion
Oscillating e-cloud
A: amplitude
: Energy
: scattering rate

4. Drude Model: Equation of motion: Amplitude Scattering rate
Free electrons: No restoring force
Neglect e-e interactions
Instantaneous Collisions
Equation of motion:
Scattering Time
Amplitude
Scattering rate

5. Change model parameters
Data analysis
Experimental Data
Generated Data
Build a model
substrate
Layer 1
Layer 2 t2 t1 1 2 ∞
Compare Exp. And Gen. data
Match ??
Well known material (Si, SiO2)
Tabulated data
- New material (NiPt, NiPtSi) Set of oscillators Solve numerically
Change model parameters NO
YES 5

6. Samples and motivation
METAL ALLOY
MONOSILICIDES Si
100 Å Ni1-xPtx
200 Å Ni1-xPtxSi Ni Pt
500˚C
30 s
100 Å Ni1-xPtx
SiO2 Si
Up to 25% Pt
SE: Drude + Drude (two carrier types)
Drude: free carriers + intraband transitions
SE: Two Drude + Lorentz
Lorentz: interband transitions
Applications: MOSFET : metal-oxide–semiconductor field-effect transistor
NiPtSi
NiPtSi 6

7. No interference fringes
Ni0.9Pt0.1/SiO2/Si (as-deposited)
100 Å NiPt
SiO2
100 Å NiPt
1040 cm-1 bond stretching vibration
~ 440 cm-1 bond rocking vibration
~ 715 cm-1 bond bending vibrations
~ 1200 cm-1 LO mode
SiO2
No interference fringes
1100 wave numbers : bond stretching absorption peak
1000 Å Ni on SiO2 7 7

8. Visible Results: Pure Ni films (0%Pt/SiO2/Si)
100 Å
200 Å
500 Å
1000 Å
No interference fringes
No interference fringes 8 8

9. Ni1-xPtx alloys: Ni/SiO2/Si
25% Pt: 250cm σDC= 30,000/Wcm (Litschel & Pop)
ħω < 1000 cm-1: σ1 with Pt
(DC: Litschel & Pop, 1985)
ħω > 1000 cm-1: σ1 with Pt
(d-intraband transitions Pt adds richer d-state band structure)
Two Drude oscillators: Two sets of electrons 1) electrons inside crystallites (grains)
2) electrons in the areas between crystallites
Nagel & Schnatterly, PRB, 1973; Hunderi, PRB 1973 9 9

10. Ni films (0% Pt): Different thicknesses
50 Å not metallic
Ola Hunderi, PRB, 1973
σ1 with t reduced grain boundary scattering in thicker films 10 10

11. Si-O vibration fitted using Gaussian oscillator.
Ni1-xPtxSi monosilicides: Ni1-xPtx/Si followed by annealing
Free carriers
d-intraband absorption
Si-O vibration
Si-O vibration fitted using Gaussian oscillator.
ħω < 1000 cm-1 : σ1 with Pt
Similar to Ni1-xPtx alloys: Ni-Pt alloy scattering
ħω > 1000 cm-1 : σ1 with Pt
More d-d interband absorption as Pt content increases 11 11

12. DC conductivity: ω 0 Pure Ni/SiO2/Si Ni1-xPtx/SiO2/Si 12
DC conductivity increases with thickness
Ni1-xPtx/SiO2/Si
DC conductivity decreases with Pt content 12 12

13. Ni1-xPtxSi monosilicides/Si
Optical conductivity decreases with increasing Pt content.
Electrical conductivity < optical conductivity 13 13

15. Ni1-xPtxSi monosilicides/Si : Eε2 versus –ε1 Drude Formula
Slope = Γ
Linear fit: eV
Model: eV
Linear fit: 0.11 eV
Model: 0.10 eV
Linear fit: 0.10 eV
Model: eV
Linear fit: 0.12 eV 15

16. Conclusion
Two carrier species in unreacted metal alloys (described by two Drude oscillators):
Separation in real space (interior or boundary of grains)
Separation in k-space (s- and d-electrons, different Fermi surface pockets)
d-intraband transitions with low energies
Unreacted metals: Conductivity depends on Pt concentration in different ways
Low frequency: Increased alloy scattering (DC-like)
High frequency: Increased d-intraband transitions: Ni(3d) and Pt(5d) mixing
Same results for Ni1-xPtxSi monosilicides.
Optical absorption (conductivity) increases with increasing metal thickness due to the reduced scattering from grain boundaries.
Low-frequency conductivity is higher for (unreacted) metals than for silicides. 16 16