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-1104934)

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

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

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

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

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

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

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

Ni1-xPtx alloys: Ni/SiO2/Si 25% Pt: σ=16,000/Wcm @ 250cm-1 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

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

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

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

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

Ni1-xPtxSi monosilicides/Si : Eε2 versus –ε1 Drude Formula Slope = Γ Linear fit: 0.058 eV Model: 0.055 eV Linear fit: 0.11 eV Model: 0.10 eV Linear fit: 0.10 eV Model: 0.091 eV Linear fit: 0.12 eV 15

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