The Characterization of Whiskers Produced by Electromigration on Suspended Aluminum Linestripes
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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Studies have shown that aluminum whiskers resulting from electromigration are as threatening to device reliability as void formation. Comparatively little research has been conducted to study their morphology or formation. This study generates whiskers on suspended aluminum tests stripes. The aluminum is evaporated onto 9 mil thick silicon wafers with a 5000 A layer of thermally grown silicon dioxide. Normal photolithography techniques are used to produce serpentine test patterns. The silicon substrate is chemically etched to produce aluminum stripes suspended on a thin layer of silicon dioxide. A current density of approximately 450,000 Asq. cm is applied to induce electromigration. The whiskers are examined with a Cambridge MK II Scanning Electron Microscope and analyzed with a JEOL 2000FX Scanning Transmission Electron Microscope. The results of the analysis show that aluminum whiskers grow in a 110 direction along the crystal axis. Additional morphological observations reveal internal dislocations and mass accumulation beneath the stripe surface at the whiskers nucleation site.
- Metallurgy and Metallography