Mechanistic Studies of Palladium Thin Film Growth from Palladium(II) -Diketonates. 2. Kinetic Analysis of the Transme
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- 作者：Wenbin Lin ; Ralph G. Nuzzo ; and Gregory S. Girolami
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：June 26, 1996
- 年：1996
- 卷：118
- 期：25
- 页码：5988 - 5996
- 全文大小：364K
- 年卷期：v.118,no.25(June 26, 1996)
- ISSN：1520-5126
文摘
The reaction pathways and kinetics for the selective deposition ofpalladium on copper from the metal-organic precursor Pd(hfac)2 have been established bymeans of reactive molecular beam-surface scatteringwherea flux of Pd(hfac)2 (ranging from 1013 to1014 molecules cm-2 s-1)impinges continuously on the copper surface.The surface selectivity of the deposition process is a consequenceof a "redox transmetalation" reaction, which isbest described by the stoichiometric equationPd(hfac)2 + Cu 
Pd +Cu(hfac)2. On polycrystalline copperfoils,the production and subsequent desorption of Cu(hfac)2from the surface occurs with unit efficiency attemperaturesbetween 400 and 600 K. At temperatures above 600 K, the yield ofCu(hfac)2 decreases and eventually falls tozeroat 800 K as the thermolytic decomposition of the hfac ligands on thesurface becomes kinetically competitive. Wehave devised a steady-state kinetic model of the adsorption ofPd(hfac)2, desorption of Cu(hfac)2,and thermolyticdecomposition of hfac molecules that quantitatively fits the decreasein Cu(hfac)2 yield seen at highertemperatures.The transmetalation reaction follows an apparent power rate lawthat is first order in Cu and first order in hfaccoverage; the preexponential factor and the activation energy for thetransmetalation reaction are A' = 2 ×10-10molecules-1 cm2 s-1 (or ~1× 106 s-1 when normalized to the surfaceatom density of Cu) and Ea' = 13 kcalmol-1.The steady-state kinetic model accurately predicts the depositionrate so long as diffusion of the Pd atoms into theCu bulk is relatively fast; for the precursor fluxes used in thepresent study, this situation holds on polycrystallinecopper foils because the grain boundaries present provide a mechanismfor the rapid interdiffusion of Pd and Cu.On a single crystal copper substrate, where the high diffusivitypathway due to grain boundaries is absent, thetransmetalation reaction is self-limiting at our precursor fluxes owingto the slower rate of atomic diffusion. Thediffusion coefficient (D) for the interdiffusion ofpalladium and copper on single crystal substrates has beencalculatedfrom a kinetic model explicitly incorporating the transport processesand is estimated to be ~10-18 cm2s-1 at 358K. The nature of multicomponent chemical vapor depositionprocesses that operate under the kinetic control ofatomic diffusion is discussed.
Pd +Cu(hfac)2. On polycrystalline copperfoils,the production and subsequent desorption of Cu(hfac)2from the surface occurs with unit efficiency attemperaturesbetween 400 and 600 K. At temperatures above 600 K, the yield ofCu(hfac)2 decreases and eventually falls tozeroat 800 K as the thermolytic decomposition of the hfac ligands on thesurface becomes kinetically competitive. Wehave devised a steady-state kinetic model of the adsorption ofPd(hfac)2, desorption of Cu(hfac)2,and thermolyticdecomposition of hfac molecules that quantitatively fits the decreasein Cu(hfac)2 yield seen at highertemperatures.The transmetalation reaction follows an apparent power rate lawthat is first order in Cu and first order in hfaccoverage; the preexponential factor and the activation energy for thetransmetalation reaction are A' = 2 ×10-10molecules-1 cm2 s-1 (or ~1× 106 s-1 when normalized to the surfaceatom density of Cu) and Ea' = 13 kcalmol-1.The steady-state kinetic model accurately predicts the depositionrate so long as diffusion of the Pd atoms into theCu bulk is relatively fast; for the precursor fluxes used in thepresent study, this situation holds on polycrystallinecopper foils because the grain boundaries present provide a mechanismfor the rapid interdiffusion of Pd and Cu.On a single crystal copper substrate, where the high diffusivitypathway due to grain boundaries is absent, thetransmetalation reaction is self-limiting at our precursor fluxes owingto the slower rate of atomic diffusion. Thediffusion coefficient (D) for the interdiffusion ofpalladium and copper on single crystal substrates has beencalculatedfrom a kinetic model explicitly incorporating the transport processesand is estimated to be ~10-18 cm2s-1 at 358K. The nature of multicomponent chemical vapor depositionprocesses that operate under the kinetic control ofatomic diffusion is discussed.