Gap fill enhancement with medium acid electrolyte for the 45nm node and below

Copper damascene interconnects technologies have introduced the use of electroplating in semiconductor. Several specific issues were brought by this typical application such as the necessity to plate in very narrow features and on large substrates while keeping electrical contacts on the edges. For this, sulfate based acidic solution coupled with additives allowing superfill behavior were introduced. Since the introduction of 200mm wafers, acidity of the bath was chosen as a compromise between transport efficiency and sufficient resistivity to ensure good plating uniformity on large diameters. Going to sub 65nm technologies, so called "low acid" electrolytes are supposed to reach their limits. In order to enhance the gap fill properties, medium acid electrolytes are being evaluated. In this study, the performances of such electrolytes are examined, first using coupons to evaluate the deposition kinetics compared to a low acid one. In order to have a first cross evaluation of their performances in integration, electrical tests are realized on 45nm node technology 300mm wafers.