Effect of Via Hole Profile on Electromigration Resistance for Via Chains

Abstract

The electromigration resistance was studied for tapered and vertical via chains of 1.2 μm in diameter with conventional sputter deposited Al films. It was shown that the electromigration resistance of the tapered via chains with a slope angle of 55° is one order of magnitude lower than that of the vertical via chains with a slope angle of 85°. The electromigration resistance for the via chains decreases with decrease in the slope angle of the via hole. The activation energies of the electromigration resistance for the vertical and tapered via chains were 0.69 eV and 0.29 eV, respectively. The mean time-to-failure (MTF) for the tapered via chains with a single PSG passivation layer is at least two orders of magnitude greater than that with a dual SiN/PSG passivation layer. It was found that SiN passivation thickness is a significant factor affecting electromigration resistance for the via chain.

Indexing terms:

• Via
• Electromigration
• Passivation