Nanoscale Cu Wiring by Electrodeposition in Supercritical Carbon Dioxide Emulsified Electrolyte

Abstract

Novel electrodeposition (ED) techniques utilizing supercritical carbon dioxide (scCO 2 ) emulsions (SCE) are introduced. ScCO 2 has low surface tension and high compatibility with hydrogen. Thus, this method is applied in fine Cu wiring to allow the complete filling of Cu into nanoscale confined space. The electrochemical reactions are carried out in emulsions composed of an aqueous electrolyte, scCO 2 , and surfactants. Three aspects in fine Cu wiring will be introduced, which are the dissolution of the Cu seed layer in the SCE, the gap-filling capability of the ED-SCE, and the contamination in the plated Cu. At first, the dissolution of the Cu seed layer in the SCE was observed. In order to prevent the dissolution of the Cu seed layer, the addition of Cu particles into the SCE was found to be effective. The electrolyte containing the SCE and the Cu particles is named scCO 2 suspension (SCS). The gapfilling capability was evaluated using test element groups (TEGs) with patterns of vias with a diameter of 70 nm and an aspect ratio of 5. Many defects were observed in the vias filled using the conventional electrodeposition (CONV) method. On the other hand, defect-free fillings were obtained by the ED-SCS method. Because of the highpressure environment needed to form the scCO 2 , the reaction cells are usually batchtype high-pressure vessels. In order to improve the feasibility of the ED-SCS technique, a continuous-flow reaction system is also proposed and examined using a round-type large-area TEG with a diameter of 300 mm. Complete fillings were obtained for vias with a diameter of 60 nm and an aspect ratio of 5 on the large-area TEG. This result was in good agreement with that of the batch-type reaction system and demonstrated the successful application of the continuous-flow system with ED-SCS.