Electroplating of Copper Conductive Layer on the Electroless-Plating Copper Seed Layer

Abstract

High resistivity and peeling have been problems with electroless copper layers preventing their use as a seed layer. Further, when copper is electroplated onto this seed layer, the resistivity is as high as 4.0 μΩ cm, much higher than the 2.2 μΩ cm value when plated on a physical vapor deposition (PVD) seed layer. This paper describes the deposition of low resistivity in copper conductive layer on the electroless-plating copper seed layer. The resistivity of the as-deposited layer decreases from 4.0 to 2.7 μΩ cm as the grain size increases from 33 to 42 nm. The grain size and resistivity of the copper layer correlate with the stress in the copper conductive layer and in seed layers. The grain growth can be enhanced by reducing the stress in the copper seed layer. A low stress and highly (111) oriented seed layer can be deposited with nucleation control. Stress reduction can also be achieved by employing the agglomeration process for the seed layer. A resistivity of 2.2 μΩ cm was attained in this conductive layer electroplated from copper hexafluorosilicate electrolytic solution on the low stress seed layer. This resistivity is comparable to the value obtained in a conventional electroplated copper layer on the PVD seed layer.