Seedless copper electroplating on Ta from an alkaline activated bath

The miniaturization of ULSI design below 32 nm requires new strategy to copper interconnect metallization. Metallization techniques forming Cu seed layer on Ta barrier film prior to feature filling by Cu electroplating cannot be effective once feature dimensions are comparable with seed layer thickness. Thus, copper electroplating has to be performed directly over a Ta barrier film (seedless deposition), while Ta thickness itself must also be significantly reduced. Copper electroplating on Ta surface from a two components injected bath is being further described in this work. Copper electrodeposition over a thin TaN/Ta barrier was performed in a two steps process; (1) Activation conducted by electrochemically reduction of Ta oxide from the TaN/Ta barrier at a negative potential of -2 V for a short period ("removal" step) and (2) copper electroplating performed in the invariable electrochemical bath by injecting a solution containing Cu-ions. Supplementary Cu plating is continued by shifting the applied potential to -1.2 V in the same electrolytic bath. It was also established that addition of low content (up to 10 ppm) dimercaptothiadiazole (DMcT) assists Cu nucleation and growth on Ta surface and allows a conformal features fillings. Copper layer deposited is characterized with an excellent adhesion to the Ta surface.