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Title: Direct Observations of Rapid Diffusion of Cu in Au Thin Films Using In-Situ X-Ray Diffraction

Abstract

In situ x-ray diffraction was performed while annealing thin film Au/Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700, 800, and 900 C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffuse through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4 kJ/mole during this initial stage, which is approximately 0.4x that for bulk diffusion and 0.8x that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defects in the sputter deposited thin film coatings. As interdiffusion continues, the two layers homogenize with an activation energy of 111 kJ/mole during the latter stages of diffusion. This higher activation energy falls between the reported values for grain boundary and bulk diffusion, and maymore » be related to grain growth occurring at these temperatures which accounts for the decreasing importance of grain boundaries on diffusion.« less

Authors:
 [1];  [1];  [2]
  1. Lawrence Livermore National Laboratory (LLNL)
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003602
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science & Technology A; Journal Volume: 24; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COPPER; DIFFUSION; GOLD; INCLUSIONS; X-RAY DIFFRACTION; THIN FILMS; ACTIVATION ENERGY; ANNEALING; FCC LATTICES; GRAIN BOUNDARIES; KINETICS; TEMPERATURE DEPENDENCE

Citation Formats

Elmer, J. W., Palmer, T. A., and Specht, Eliot D. Direct Observations of Rapid Diffusion of Cu in Au Thin Films Using In-Situ X-Ray Diffraction. United States: N. p., 2006. Web. doi:10.1116/1.2204926.
Elmer, J. W., Palmer, T. A., & Specht, Eliot D. Direct Observations of Rapid Diffusion of Cu in Au Thin Films Using In-Situ X-Ray Diffraction. United States. doi:10.1116/1.2204926.
Elmer, J. W., Palmer, T. A., and Specht, Eliot D. Sun . "Direct Observations of Rapid Diffusion of Cu in Au Thin Films Using In-Situ X-Ray Diffraction". United States. doi:10.1116/1.2204926.
@article{osti_1003602,
title = {Direct Observations of Rapid Diffusion of Cu in Au Thin Films Using In-Situ X-Ray Diffraction},
author = {Elmer, J. W. and Palmer, T. A. and Specht, Eliot D},
abstractNote = {In situ x-ray diffraction was performed while annealing thin film Au/Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700, 800, and 900 C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffuse through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4 kJ/mole during this initial stage, which is approximately 0.4x that for bulk diffusion and 0.8x that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defects in the sputter deposited thin film coatings. As interdiffusion continues, the two layers homogenize with an activation energy of 111 kJ/mole during the latter stages of diffusion. This higher activation energy falls between the reported values for grain boundary and bulk diffusion, and may be related to grain growth occurring at these temperatures which accounts for the decreasing importance of grain boundaries on diffusion.},
doi = {10.1116/1.2204926},
journal = {Journal of Vacuum Science & Technology A},
number = 4,
volume = 24,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • In-situ x-ray diffraction was performed while annealing thin-film Au/Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700 C, 800 C, and 900 C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffusemore » through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4 kJ/mole during this initial stage, which is approximately 0.4x that for bulk diffusion and 0.8x that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defects in the sputter deposited thin film coatings. As interdiffusion continues, the two layers homogenize with an activation energy of 111 kJ/mole during the latter stages of diffusion. This higher activation energy falls between the reported values for grain boundary and bulk diffusion, and may be related to grain growth occurring at these temperatures which accounts for the decreasing importance of grain boundaries on diffusion.« less
  • Differential scanning calorimetry (DSC) and in situ X-ray diffraction experiments on stoichiometric AuCu are reported. Enthalpy peaks of successive transitions AuCu I (L1[sub 0]) [r arrow] AuCu II and AuCu II [r arrow] disorder (Al) are observed, and their integration leads to [Delta]H values of 2.5 and 9.4 J/g, respectively. These successive transitions are well seen in in situ diffraction. Each transformation is spread over a temperature range, and it is shown that the transition AuCu I (L1[sub 0]) [r arrow] AuCu II starts at a temperature as low as 350 C. Some kinetic studies were performed. The long-range ordermore » parameter evolution against time is estimated for the ordering at 300 C into L1[sub 0] from quenched disordered AuCu. The AuCu I (L1[sub 0]) [r arrow] AuCu II was also studied from a kinetic point of view, using the intensities of characteristic lines. Various results are compared with previously reported observations and discussed.« less
  • Ultrathin TaN and Ta 1-xAl xN y films with x = 0.21 to 0.88 were deposited by atomic layer deposition (ALD) and evaluated for Cu diffusion barrier effectiveness compared to physical vapor deposition (PVD) grown TaN. Cu diffusion barrier effectiveness was investigated using in-situ ramp anneal synchrotron X-ray diffraction (XRD) on Cu/1.8 nm barrier/Si stacks. A Kissinger-like analysis was used to assess the kinetics of Cu 3Si formation and determine the effective activation energy (E a) for Cu silicidation. Compared to the stack with a PVD TaN barrier, the stacks with the ALD films exhibited a higher crystallization temperature (Tmore » c) for Cu silicidation. The Ea values of Cu 3Si formation for stacks with the ALD films were close to the reported value for grain boundary diffusion of Cu whereas the Ea of Cu 3Si formation for the stack with PVD TaN is closer to the reported value for lattice diffusion. For 3 nm films, grazing incidence in-plane XRD showed evidence of nanocrystallites in an amorphous matrix with broad peaks corresponding to high density cubic phase for the ALD grown films and lower density hexagonal phase for the PVD grown film further elucidating the difference in initial failure mechanisms due to differences in barrier crystallinity and associated phase.« less
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  • The formation and growth of sigma ( ) phase in 2205 duplex stainless steel (DSS) was observed and measured in real time using synchrotron radiation during 10 hour isothermal heat treatments at temperatures between 700 C and 850 C. Sigma formed in near-equilibrium quantities during the isothermal holds, starting from a microstructure which contained a balanced mixture of metastable ferrite and austenite. In-situ synchrotron diffraction continuously monitored the transformation, and these results were compared to those predicted by thermodynamic calculations. The data were further analyzed using a modified Johnson-Mehl-Avrami-Kolmogrov (JMAK) approach to determine kinetic parameters for sigma formation over thismore » temperature range. The initial JMAK exponent, n, at low fractions of sigma was found to be approximately 7.0; however, toward the end of the transformation, n decreased to values of approximately 0.75. The change in the JMAK exponent was attributed to a change in the transformation mechanism from discontinuous precipitation with increasing nucleation rate, to growth of the existing sigma phase after nucleation site saturation occurred. Because of this change in mechanism, it was not possible to determine reliable values for the activation energy and pre-exponential terms for the JMAK equation. While cooling back to room temperature, the partial transformation of austenite resulted in a substantial increase in the ferrite content, but sigma retained its high-temperature value to room temperature.« less