Effect of Silicon Inclusions on the Reliability of Sputtered Aluminum-Silicon Metallization

A higher than average failure rate-was recorded during high-temperature life testing of a vendor 16K SRAM. Failure analysis of the fallout determined the predominant failure mode to be open metal bit-lines at a topography step in the array. A unique method of unlayering-was used which left all metal-line constituents intact. Rather than finding physical voids in the lines, silicon nodules were found. The formation and possible subsequent growth of nodules is related to wafer-process parameters and life stress, eventually leading to an electromigration-type failure. Special test sites were used to substantiate failure modes and mechanisms found on functional product.