Critical Accelerator Concentration for Understanding Superfilling of Copper Electrodeposition

Abstract

Bis(3-sulfopropyl) disulfide (SPS) and polyethylene glycol (PEG) are typical accelerators and suppressors used for Cu electrodeposition to achieve via/trench superfilling in microelectronic manufacturing. Various models have been proposed and verified to explain the superfilling phenomenon. However, molecular-level details regarding the adsorption and interactions of these additives remain scarce. Herein, electrochemical and wide-frequency detection attenuated total reflection surface-enhanced infrared absorption spectroscopic (ATR-SEIRAS) measurements of varying SPS concentrations in the presence of PEG were conducted to investigate its influence on the depolarization behavior, Cu electrodeposition performance, and adsorption structure. The results revealed a critical accelerator concentration (CAC) at 5 ppm of SPS under the present conditions. Below the CAC, the acceleration effect increases sharply with the SPS concentration, and above the CAC, it is only very mildly dependent on the concentration. ATR-SEIRAS results revealed that the tilted adsorption of SPS manifested by the band intensity of the sulfonate asymmetric stretching and Cu electrodeposition efficiency are linearly correlated. The orientation of the sulfonate group in the adsorbed SPS is concentration-dependent: below CAC, the sulfonate group on average is closer to the surface, and above CAC, it is further away from the surface. In addition, the time-dependent evolution of additive vibration bands provides direct molecular evidence that PEG adsorption is rapid and that SPS adsorption is slow. A mechanistic comprehension of superfilling in the framework of CAC is also provided. This work demonstrates the significant role of CAC in achieving superfilling and may provide some guidance in the rational adjustment of practical additive concentrations for various microscale vias/trenches.