Method and apparatus for monitoring in-line copper contamination

Abstract

A method for determining copper contamination on a semiconductor wafer is disclosed. The minority carrier diffusion length is measured, then the wafer is activated by the application of optical or thermal energy. Likely the wafer is also contaminated with iron and thus it is necessary to separate the diffusion length effects caused by the iron from those caused by the copper, that is, both copper and iron contaminants cause a reduction in the minority carrier diffusion length. The applied energy causes the iron-boron pairs to dissociate and also causes the copper to form a metastable copper silicide state. After about 24 to 36 hours, the iron-boron pairs reform and therefore the iron contaminants no longer influence the diffusion length. At this point the diffusion length is measured again, which values are due solely to the copper contamination, since the copper remains in the silicide state. The copper contamination can be determined from the measured diffusion length values.

Dependencies are inferred from the claim text.