Pretreatment to assure the copper filling in through-silicon vias

Abstract

Copper seed layer repair and pre-wetting are standard operation procedures (SOPs) for copper filling with void-free, through-silicon vias (TSVs). In this paper, a novel pretreatment with pre-wetting and cleaning is investigated based on the results of copper filling in via when copper oxide is present on the surface of the seed layer. The pre-wetting and cleaning are integrated into one step in the pretreatment. Basic Electrolyte Solution (BES) is chosen to be pre-wetting acidic liquid. A copper seed layer formed on a wafer by sputter deposition was put into chamber to grow native copper oxide. To investigate the damage of the pretreatment, the corrosive rate of BES was measured by cathodic chronopotentiograms. The results show that BES can clean the copper oxide on the surface of the seed layer without corroding the copper seed layer. The combined pre-wetting and cleaning, pretreatment simplifies the SOP, especially for copper oxide on the seed layer. The conclusions drawn from the experimental results were employed in TSVs. Furthermore, there is one essential requirement for the pretreatment: the thickness of the copper seed layer must be more than 5 nm after the copper is oxidized on the surface of the seed layer.