(Invited) Electrodeposition of Copper and Cobalt in Presence of Some Organic Additives
Authors: Huang Qiang , Lyons Tyler W. , Hu Yang , Sides William D. 
Published: February 2020

Electroplated damascene copper has been used for more than 20 years for interconnects in semiconductor and microelectronic industry1. As the structures continue to scale, the coarse grains formed during annealing become increasingly difficult to extend into the fine structures, resulting in higher resistance and poorer electro-migration. While such difficulty in grain growth relates to the geometrical confinement of fine structures itself, the impurity incorporation from organic additives used in electrolyte was also found much higher2, 3 and is expected to impede the grain growth4. However, impurity elements such as carbon, oxygen, sulfur, and chloride are typically incorporated together and increase or decrease simultaneously. The first part of this talk presents a study where we used ion implantation to dissect the effects of each elements separately, aiming to identify the elements that have the dominant effect on copper grain growth. The different copper grain growth behaviors in presence of different impurity elements will be discussed.

Figure 1 shows the top down focus ion beam image of copper films implanted with the same amount of chlorine and carbon after annealing at different temperatures. While both elements impeded copper grain growth compared with as-plated copper, a stronger inhibition effect in the nucleation of coarse grains at low temperature was observed for chlorine. However, an instantaneous nucleation followed by a more abnormal grain growth was observed for chlorine, resulting in a fully transformed film with uniform grain size at 400 C. On the other hand, carbon continue to inhibit the grain nucleation at high temperature and the film was only partially transformed even at a high temperature of 400 C.

On the second part of the talk, electrodeposition of cobalt in presence of a class of additives, dioxime, will be presented. Copper suffers a rapid increase in its resistivity when the critical dimension of structures falls below the electron mean free path of copper, 38 nm5. On the other hand, cobalt is of interest as a candidate to replace copper in the metallization because of its much shorter electron mean free path of 7 to 11 nm6. The presence of dimethylglyoxime was found to suppress cobalt electrodeposition, which makes it of interest for metallization. Various of dioxime molecules are characterized and compared. A surface adsorbed complexed species between cobalt cation and oxime is proposed to result in the suppression.

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