Bottom-up through Silicon Via Filling Using Galvanostatic Cu Electrodeposition with Three-Additive Chemistry
Authors: Kim Hoe Chul , Kim Myung Jun , Choe Seunghoe , Cho Ji Yoon , Lee Donghyung , Jung Il , Cho Won-Seob , Kim Jae Jeong 
Published: February 2020

Three-dimensional packaging of microelectronic devices has been investigated for realizing a multi-functional single device. Through silicon via (TSV) is recognized as a promising technology to enhance the performance of emerging devices [1,2].
Several mechanisms of TSV filling using Cu electrodeposition have been reported from the previous researches; V-shape bottom-up filling induced from the concentration gradient of leveler [3], or extreme bottom-up filling through the selective disruption of suppressing adsorbates [4]. In this research, trenches of several sizes were galvanostatically filled with accelerator (bis(3-sulfopropyl)disulfide, SPS), and chemically synthesized suppressor and leveler, designated as S1, S2, L1 and L2. Suppressors are kinds of polymer, and S1 contains amine group having molecular weight between 3000 and 4000. The molecular weight of S2 is between 2000 and 3000. Both L1 and L2 are kinds of pyridine that includes a few nitrogen atoms, though they have different functional groups each other. The void-free filling was achieved with a filling mechanism distinguished from the previous reports.
Filling profiles of trenches according to the deposition time are shown in Figs. 1 [5] and 2 in the presence of SPS-S1-L1 and SPS-S2-L2, respectively. In both Figs. 1 and 2, it was observed that Cu deposition was strongly suppressed at the top of the trenches until the end of the filling. The growing surface was established at the bottom of trench, resulting in a successful bottom-up filling of Cu.
Although practically similar deposition profiles were observed regardless of the given additive chemistry, the microstructure of Cu near the opening of TSV was different in Fig. 1(f) and 2(f). With the addition of S1 and L1, the microstructure was changed from smooth at the bottom to coarse one at the top. Coarse microstructure possibly contains voids, being a drawback of S1-L1. The microstructure was improved by introducing other combinations of additives, S2 and L2.
Based on our electrochemical analyses and gap-filling experiments, we suggested the detailed mechanism of galvanostatic bottom-up filling in Fig. 3, applicable to both Figs. 1 and 2. The electrodeposition was strongly inhibited at the top and sidewall near TSV opening, originated by co-adsorption of leveler and suppressor. At the bottom of trench, the growing surface was established via the accumulation of SPS, which induced the extreme bottom-up filling.
In this presentation, we will introduce a galvanostatic filling mechanism, strong inhibition at the top and sidewall, along with the accumulation of SPS at the bottom, to explain the void-free and fast bottom-up filling achieved within 20 min.

References

1. K. J. Park, M. J. Kim, T. Lim, H.-C. Koo, and J. J. Kim, Electrochem. Solid-State Lett., 15, D26 (2012).
2. S. K. Cho, M. J. Kim, and J. J. Kim, Electrochem. Solid-State Lett., 14, D52 (2011).
3. T. Hayashi, K. Kondo, T. Saito, M. Takeuchi, and N. Okamoto, J. Electrochem. Soc., 158, D715 (2011).
4. T. P. Moffat and D. Josell, J. Electrochem. Soc., 159, D208 (2012).
5. M. J. Kim, H. C. Kim, S. Choe, J. Y. Cho, D. Lee, I. Jung, W.-S. Cho, and J. J. Kim, J. Electrochem. Soc., submitted.

Figure Captions

Figure 1. Filling profile according to the filling time of (a) 2.5, (b) 5, (c) 7.5, (d) 10, (e) 15, and (f) 20 min with applying 6.5 mA/cm2 in the presence of SPS-S1-L1 [5].
Figure 2. Filling profiles according to the filling time of (a) 2.5, (b) 5, (c) 7.5, (d) 10, (e) 15, and (f) 20 min with applying 10 mA/cm2 in the presence of SPS-S2-L2.
Figure 3. The schematic diagram of filling mechanism.