Title: Electrodeposition and Electroless Deposition of Copper in Interconnect Technology and Biotechnology Related Applications
Description: Electroless copper deposition is a promising alternative technique for interconnect fabrication because it may be difficult for electrodeposition to fill features that are 10 nm and smaller. An electroless copper bath of low toxicity and mild operating conditions with dimethylamine borane (DMAB) as reducing agent was examined. The results were interpreted within the framework of mixed potential theory, and a strong catalytic effect of the presence of the anodic reaction to the cathodic reaction was observed, possibly due to a significant pH decrease near the electrode that impacts the chelation of cupric ions. It was also found that the nucleus density not only depends on the type of substrates, but is also controllable by pH, temperature and the addition of PEG. Whether electroless deposition will be implemented in manufacturing is dependent on continued improvements in electrodeposition, and organic additives play a major role in efficacy. Development of advanced additives continues, and two lab scale tools that facilitate additive studies are designed and implemented.

A membrane-separated cell was developed to effectively differentiate additive aging on the cathode side and anode side. Additive behavior in the cell was characterized by cyclic voltammetric stripping (CVS), and a significant aging effect of bis (3-sulfopropyl) disulfide (SPS) on the cathode side was observed. The rate of aging increases at higher acid level and lower current density, yet decreases in the presence of PEG. Complex wafer plating tools have been developed for use in manufacturing to guarantee a high uniformity of copper electrodeposition. Wafer size tools were “scaled down” for lab use by introduction of a simple insulating shield system for coupon size plating studies to avoid poor current distribution. By numerical simulation, sensitivities of parameters were systematically studied, with which the optimum shield design was made. The design reduced the spatial variation in current density from 18% to only 3%. Copper deposition can be applied to other applications, and naturally constraints on processing can be very different.

For example, for biosensor applications, copper deposition can be a signal amplification method of binding to engineered phages. Chapter 5 demonstrates the use of electroless copper deposition to image phage with both high sensitivity and low operational time and cost. A correlation between copper quantity and phage concentration was established, with a limit of detection in ppt level. A pre-concentration device can be utilized to detect phage of lower concentrations without significantly increasing the time for detection. In another example, copper deposition may be used in an integrated process to produce a biofuel. Here, the process is akin to copper electrowinning processes albeit with modified electrolytes. A design of the electrowinning cell was built in-house and showed product yield capability and scalability to serve the bioreactor. Lower cell potentials were demonstrated by utilizing novel mixed metal oxides anodes. Copper deposit adhesion depended on electrolyte composition, and this impacts bioreactor performance.

The current efficiency during electrowinning is between 70% and 90% depending on electrolyte composition.