In Situ X-ray Fluorescence Measurements During Atomic Layer Deposition: Nucleation and Growth of TiO 2 on Planar Substrates and in Nanoporous Films 1 and In-Situ Synchrotron X-Ray Scattering Study of Thin Film Growth by Atomic Layer Deposition 2 Matthew Weimer In partial fulfillment of Phys 570 Spring April 30, 2012
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What is Atomic Layer Deposition? Chemical Vapor Deposition Atomic Layer Deposition
ALD nucleation and nanoporous growth study by XRF performed at NSLS
ALD chamber for X-ray studies (a) Schematic representation of the top view of in-situ x-ray fluorescence ALD reaction chamber. (b) Photograph of the ALD chamber at beamline X21 of NSLS.
Incident Photon Energy: 8 kev with Si (111) double crystal monochromator X-ray beam size 0.5 X 0.5 mm 2 and incident angle kept at 5 Collected with silicon drift detector perpendicular to sample surface Penetration depth of 8 kev x-rays on TiO 2 is 1.6 μm From Fresnel equations Λ = 1 2kIm(q ) Λ = 1.6 μm TiO 2 films Thus, Ti Kα 1 (L 3 to K transition) intensities (4.5 kev) are proportional to film thickness Normal absorption experiments not available, T too small T = I = e μz I o
3 Types of surfaces Thermally Grown SiO 2 Si O Si H O H O Si Si H O Si HF treated SiO 2 H O O H O H O H O H ALD deposited AL 2 O 3 on SiO 2 H H H O O O O Al Al Al Al Al
μ = ρ mn A M σ a σ a ~ Z4 E 3 First Order Perturbation Theory to get σ a σ a = 2π V 2 ħc 4π 3 M if = i H l f \M if \ 2 δ(e f E i )q 2 sin θ dqdθdϕ H l =ep A m + e2 A 2 2m i = 1 γ 0 e f = γ 0 e 1 Zeolite-4 3 σ a = 32λr 0 4 3 ω A 2 ω k ω c 5 2 2π e 4 Reference
Grazing-incident X-ray Diffraction (GIXD) and XRR on Ru thin films deposited by ALD performed at the PLS
Incident Photon Energy: reflectivity 11.6keV (1.069 Å) and diffraction 8keV (1.540 Å) Max scattering angles of reactor: 60 (vertical) and 25 (lateral) High flux required for low intensity from initial growth layers 10 13 Photons 130 pole undulator, 2 cm periodic length
Surface Roughness calculated by reflection intensity From Fresnel equations r(q) = Q Q Q+Q Λ = 12.3 μm Ru films X-rays weakly scattered: kinematical approximation Reflection by a homogeneous slab r thin slab i 4πρr 0 Q Q 1 = i λρr 0 sin α
Now include a Debye-Waller-like factor r (Q) = i 4πρr 0 Q e (Q2 σ 2 ) Film on substrate creates Keissig fringes Where σ is proportional to rms roughness Film thickness proportional to period ( Q)of oscillation Thickness = 2π Q Amplitude of fringes diminishes as average surface roughness increases 3,4
In-plane structure (green) F hkl (Q) = e iq R n f j (Q)e iq r j n j Scattering events restricted by Laue condition Q = G Out-of-plane structure (red) Crystal truncation rods extended along z F CTR = A(Q) e iq lj z = A(Q) 1 e iq l z j=0 I CTR = F CTR 2 = A Q 2 4 sin 2 (πl)
Synchrotron in-situ GIXD on-line Image Plate Synchrotron ex-situ GIXD diffractometer and scintillation
Advancements have been made regarding the in-situ characterization of thin films with synchrotron radiation X-ray fluorescence and x-ray reflectivity are non-destructive techniques to elucidate film thickness GIXD provides a picture of crystalline phases during film growth Together can be used to determine nucleation mechanisms for many thin films deposited by ALD
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