Room-temperature diffusion in Cu/Ag thin-film couples caused by anodic dissolution
- PDF / 699,789 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 223 Views
I.
INTRODUCTION
VACANCIES may be formed during anodic dissolution and corrosion. Figure 1 shows the mechanism suggested by Pickering and Wagner,[1] in which vacancies are formed when subsurface atoms jump into surface kinks or ledges on a dissolving crystal surface. Forty[2] originally suggested that vacancies produced by dezincification may interact with dislocations to produce stress corrosion cracking (SCC) in brass. Pickering and Wagner[1] further implicated vacancies as the cause of dealloying in brasses. Revie and Uhlig[3] postulated anodically generated vacancies to explain enhanced creep during anodic dissolution of copper. One of the present authors[4] proposed that the processes causing increased creep may also play a role in the mechanism of SCC and corrosion fatigue. Meletis[5] suggests that corrosion-generated vacancies are attracted to dislocations, modify dislocation configuration, and produce embrittlement by SCC. Magnin et al.[6] and Aaltonen et al.[7] also have recently suggested a role for corrosion-generated vacancies in the mechanism of SCC. The present authors reported initial experimental evidence of anodically generated vacancies in Cu/Ag thin-film diffusion couples[8] and more recently presented subsequent results along with preliminary observations on data analysis and mechanism.[9] This article describes the completed analysis of the diffusion data along with further theoretical interpretations. II.
EXPERIMENTAL PROCEDURES
The Cu/Ag diffusion couples were prepared using magnetron sputter deposition on commercially available pol-
DENNY A. JONES, Professor, is with the Chemical and Metallurgical Engineering Department, University of Nevada, Reno, NV 89557. ALAN F. JANKOWSKI, Metallurgist, is with the Lawrence Livermore National Laboratory, Livermore, CA 94550. GAIL A. DAVIDSON, Process Engineer, is with Intel Corporation, Rio Rancho, NM 87124. Manuscript submitted June 20, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
ished Si (111) wafers, which provided a convenient, reproducible substrate for deposition with no apparent further role in subsequent processes. In the evacuated deposition chamber, vertical Si wafers were rotated horizontally past 0.999 pure Ag and Cu magnetron sources, ensuring that layer thicknesses were uniform over each sample surface and from sample to sample. Independent measurements showed maximum errors of 5 pct in calculated layer thicknesses. A 100-nm base layer of Ag was deposited first on each Si-wafer substrate, followed by a 100-nm Cu layer on the Ag base layer. X-ray diffraction characterization indicated that the Cu and Ag films grew epitaxially in a (111) orientation on the Si substrate. Preliminary examinations revealed a grain size in the Ag and Cu layers of about 1 m m. Rutherford backscattering (RBS) analysis showed a compositionally discrete interface between the Cu and Ag layers. Each of the 5-cm-diameter wafers with Ag and Cu deposited layers was cut into several specimens of approximately 1.3 3 2 cm. Each specimen was coated with fingernail p
Data Loading...
