Bath chemistry and copper overburden as influencing factors of the TSV annealing

Abstract

The outlined investigations represent a new systematic approach for the characterization of the copper annealing behavior in TSVs. In the center of interest are the changes in material behavior caused by bath chemistry compositions and deposition parameters during the ECD copper fill. In addition the effects on annealing behavior with or without Cu overburden are evaluated. Therefore, two bath chemistries were used for the Cu fill of one TSV test die layout. Moreover, half of the die samples underwent overburden CMP. The resulting four test die groups underwent annealing at identical conditions. The subsequent characterization featured protrusion, warpage and EBSD measurements. Results show a direct link of crystallographic defect reductions towards the tendency of developing Cu protrusion. Also deviations in warpage and crystal structure development for annealing with or without Cu overburden are presented. In conclusion the outlined investigation gains information how the Cu crystal structure develops in TSVs during annealing and links this behavior to thermo-mechanical effects like protrusion and warpage. This paper demonstrates that this behavior is dependent on the applied bath chemistry and that the presence of an overburden layer also has an influence. Deductions for an improved TSV manufacturing process can be derived from the achieved results.