Copper interconnect technology faces limitations due to the electron’s mean free path and electromigration, driving the adoption of cobalt alternatives. This study proposes a novel mechanism to achieve superfilling by tuning the adsorption energy of additive molecules on cobalt surfaces. The adsorption energies of additives are tailored by changing molecular structures with different functional groups. Computational results reveal that carbon–carbon triple bonds critically strengthen adsorption, while ether bonds further enhance binding on distinct cobalt crystallographic planes. Specifically, 1,4-bis(2-hydroxyethoxy)-2-butyne (BEO) containing both triple bonds and ether groups exhibits the highest adsorption energy (−22.62 eV). Replacing ether with hydroxyl groups in 2-butyne-1,4-diol (BOZ) reduces the adsorption energy to −10.39 eV, while eliminating triple bonds in 1,4-butanediol diglycidyl ether (BDE) further decreases it to −8.43 eV. Experimental studies demonstrate that BOZ and BEO preferentially adsorb on the (101) and (110) planes of hexagonal close-packed cobalt (HCP-Co) due to their differential adsorption energies. This selective suppression promotes preferential growth along the densely packed (002) orientation. This leads to a trench-filling process dominated by the most densely packed plane, resulting in better electrical performance. Superfilling is achieved when molecular adsorption energies are in the range of 5–8 eV. The work establishes a functional group design strategy to regulate additive adsorption, enabling crystallographic control for advanced cobalt electrodeposition processes.
Yunwen Wu,Mengyun Zhang,Yuhang Jiang,Yiting Tong,Pengfei Chang,Tao Hang,Ming Li
Electrodeposition is a key technology for 3D interconnect in electronic devices, while additives play an essential role in realizing super-filling in 3D interconnect. In this work, the impact of phenyl methyl sulfoxide (PMSO) on cobalt electrodeposition is studied and the underlying mechanism is explored. It is demonstrated that PMSO exhibits excellent inhibition ability even at relatively low concentrations due to its high chemical reactivity, contributed by the active sulfoxide group. We find that a proper concentration (20 ppm) of PMSO is important to achieve low surface roughness around 3.9 nm and uni-hcp (002) orientation due to the effective surface absorption. The nucleation of cobalt is altered to progressive nucleation under the influence of PMSO from instantaneous nucleation in the absence of PMSO, resulting in an even cobalt deposition behavior. Furthermore, the presence of PMSO enhances the wettability and enables the super-filling of cobalt TSV trenches with high quality, thereby indicating that PMSO is an effective additive for practical applications.
Yicai Wu,Zijie Mao,Tian-Wen Jiang,Xianxian Qin,Kun Jiang,Shouzhong Zou,Wen-Bin Cai
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.
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