Void control during plating process and thermal annealing of through-mask electroplated copper interconnects

•Void free through-mask electroplated Cu interconnect was achieved.•Wet etching was used to enhance the wettability of the seed layer.•TaN passivation layer can prevent void-formation in the annealing process.•The reported Cu interconnect shows good electric performance.

The quality of the sputtered copper film, which serves as the seed layer for sequent electroplating, becomes critical when the size of crack on the surface of the sputtered film is close to the feature size of the electroplated copper interconnect. The crack results in void formation in electroplated copper before thermal annealing and this phenomenon limits attainable highest anneal temperature. To solve this problem, the sputtered seed layer was slightly etched before electroplating process and a TaN passivation layer was deposited on the electroplated Cu interconnect before thermal annealing. Those processes not only suppressed void formation during the electroplating and annealing process at 300 °C, but also resulted in lower electrical resistance in the copper interconnects.