Silver-Magnesium Thin Film Interactions in an Oxidzing Ambient
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Date
1999
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University of the Western Cape
Abstract
Silver has the lowest resistivity of all metals and its good electromigration properties make. it a possible candidate to replace Al in microelectronics circuits. However, silver suffers from several drawbacks. Some of the drawbacks are the difusion of Ag into SiO2, poor adhesion to SiO2, and corrosion of silver when exposed to
ambients such as H2S and C}i. To overcome these stability problems, we need diffusion barriers to prevent interdifusion of Ag into SiO2, an adhesion promoter to improve adherence, and a passivation layer to protect the silver against corrosion. Ag(200 nm)/Mg(50 nm) bilayer structure on SiO2 substrates were annealed at temperatures ranging from 300-650°C and times from 30-120 min in a flowing Ar ambient. Upon annealing the Mg segregates to the surface where it reacts with the residual O in the Ar to form a Mg-oxide passivation layer of ~35nm. RBS and AES analysis of the samples indicates that out diffusion of Mg occurs at 350°C, and that reaction is completed at 500°C. Within the detection limits of the analysis techniques used, no interfacial reaction between Mg and SiO2 could be detected. The resistivity of the encapsulated silver films is about 4.3μQ -cm. XRD analysis revealed that no intermetallic compounds could be detected.
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Keywords
diffusion barriers, passivation layer, magnesium, microelectronics, silver