A method is introduced for Cu bottom-up filling at trenches with dimensions similar to those of through silicon via in the presence of three organic additives. The electrodeposition is galvanostatically conducted, and the potential-time curves during the gap-filling and the evolution of deposition profiles according to the deposition time are investigated to clarify the mechanism of the Cu bottom-up filling. The role of each organic additive is examined by electrochemical analyses and the gap-filling profiles with various combinations of organic additives. Based on the results, the gap-filling mechanism regarding the surface coverages of organic additives is suggested. The bottom-up filling of Cu is achieved with the establishment of growing surface at the bottom of trench via the accumulation of accelerator and the strong obstruction of Cu reduction at the side wall and top surface by inhibiting adsorbates. Trenches with 40 μm depth and widths of 6 or 8 μm are filled using the suggested mechanism within 15 min.

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The chemically synthesized suppressor and leveler are added together with bis(3-sulfopropyl)disulfide (SPS) to galvanostatically fill up the trenches with the similar dimensions to those of the through silicon vias. In our previous study, the deposition of the coarse-grained Cu was indicated as a drawback of the synthesized additives, i.e., polyoxy polymer with amine terminal groups and pyridine derivatives containing additional amine groups. In this study, the modified chemistry of organic additives is used, enabling the bottom-up filling of trenches and improving the microstructure of the deposited Cu. The conversion of the functional groups from amine to hydroxyl groups in both the suppressor and leveler, and the uniform adsorption of modified suppressor improved the microstructure of the deposited Cu. The void-free trench filling is induced by the selective adsorption and accumulation of SPS at the bottom and negligible deposition on the top and side-walls of the trenches. Based on the filling mechanism, the trenches with 9 μm width and 50 μm depth are galvanostatically filled in ≤20 min. Intensive researches have been focused on the fabrication of 3-dimensional (3D) interconnection among electronic devices to achieve a high-density integration and multifunctional single device.1-3 The metallization of through silicon vias (TSVs), one of a promising technology for the 3D packaging, is expected to enhance the operation speed and performance of the microelectronic devices.4-8 A void-free filling of the TSVs by Cu electrodeposition with proper organic additives chemistry has been actively investigated to reduce processing time. 9-11A concentration gradient of suppressing agent, high at the via top while decreasing gradually toward the via bottom, typically induces a bottom-up via filling. The Cu deposit according to the filling time typically reveals a V-shaped profile reflecting the gradient of additive coverage. [12][13][14] Recently, an extreme bottom-up filling of the vias was achieved using one component of additive, suppressor, resulting in a clearly flat filling profile rather than the V-shape. 15,16 Based on the previous results, L. Yang et al. reported that the difference in the adsorption density of suppressing agents between the via top and bottom was required for a void-free bottom-up filling. 17Moreover, the accumulation of accelerator at the bottom of the via was also highlighted in understanding the filling mechanism. In the case of recessed features with submicrometer dimensions, accelerators including bis(3-sulfopropyl)disulfide (SPS) promoted copper deposition, enabling the superconformal filling in the combination with suppressors, based on a curvature-enhanced-accelerator coverage (CEAC) mechanism.18-26 However, the same additive composition or deposition method used in the CEAC model itself mostly failed in the void-free filling of the TSVs. Therefore, additional steps including the selective deactivation of the adsorbed SPS on the top of the vias were introduced to improve the filling perf...

Through silicon via (TSV) technology has been researched for 3-dimensional packaging of electronic devices, and Cu electrodeposition has been used for TSV filling. The organic additives are one of the most important factors in Cu electrodeposition affecting Cu gap-filling, and the leveler usually plays a decisive role. In this research, iodide ion (I − ) is adopted instead of organic leveler for Cu bottom-up filling. The behaviors of I − are investigated by various types of electrochemical analyses. Especially, the influences of I − on the adsorption of the accelerator and suppressor are extensively studied, and it is confirmed that I − makes the suppression layer robust while reducing the adsorption of the accelerator. Also, it was observed that the effect of I − is greater under the strong convection of electrolytes than without convection, meaning that I − could induce selective deposition at the bottom of the features. Based on this, TSV-scaled trenches are successfully filled by potentiostatic Cu electrodeposition in the presence of the accelerator, suppressor, and I − without any organic levelers.

The degradation of bis(3-sulfopropyl) disulfide (SPS) during Cu electrodeposition and the influence of its decomposition products on the Cu film properties are investigated. SPS decomposes into 3-mercapto-1-propane sulfonic acid (MPSA) and 1,3-propane disulfonic acid (PDS) by dissociation of the disulfide bond and oxidation reactions. The MPSA seems to recombine to form SPS through a reaction with cupric ions, whereas the PDS accumulates in the plating solution without any further reactions. It was found that the net conversion from SPS to PDS reduced the acceleration effect and resulted in the deterioration of Cu feature filling. The final decomposition product, PDS, caused no remarkable changes in either the electrochemical behavior or the film properties. The deterioration in feature filling by degradation of SPS is mainly associated with the decrease in SPS concentration by decomposition and incorporation.

A leveler is one of the key additives for the defect-free filling of Through Silicon Via. The convection dependent behavior of a leveler is required to achieve successful gap-filling of Cu. Levelers occasionally contain charged functional groups and the counter anions. The charged functional groups obviously determine the characteristics of the leveler, and counter anions also influence the electrochemical behavior and Cu gap-filling. In this study, we synthesize levelers that have two quaternary ammoniums and different counter anions. The electrochemical behavior of the synthesized levelers and the effect of the counter anions on Cu gap-filling are described.

The reduction of filling time is one of the current challenges in through silicon via (TSV) filling by Cu electrodeposition. Electrodeposition rate can be increased with higher current density; however, it can result in the formation of voids due to a negative shift in the potential, which can deteriorate the effect of organic additives for TSV filling. In this work, we introduce thiourea to increase the inhibition of additives on the side walls of TSV against Cu deposition. It was found that thiourea increases the inhibition effect of the suppressor, which leads to the reduction of filling time by half.

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