Bromide Ion as a Leveler for High-Speed TSV Filling

Abstract

Organic levelers have been essential additives for Cu electrodeposition to achieve defect-free filling of through-silicon vias (TSVs). They selectively inhibit Cu deposition on top of TSVs, avoiding the occlusion of TSV openings and concentrating Cu deposition inside the TSVs. We recently reported that iodide ions (I − ) can act as an inorganic leveler to induce defect-free TSV filling. However, it was found that I − considerably decreased the efficiency of Cu electrodeposition because of the formation of an unstable CuI suppression layer on top of the wafer. The CuI layer easily detached from the wafer, and additional electrons were consumed to reestablish the suppression layer during gap-filling. This study introduces a TSV filling process with bromide ions (Br − ) as an alternative to I − . Although the suppression strength of Br − to Cu electrodeposition is weaker than that of I − , Br − forms a more stable suppression layer that does not reduce the efficiency of Cu electrodeposition, enabling high-speed TSVs filling. As a result, the filling rate with Br − was twice as fast as that with I − at the same applied current density; thereby TSVs 60 μm deep and 5 μm in diameter were completely filled in 500 s.

Through Silicon Via Filling with Suppression Breakdown of PEG–Br– in Absence of Accelerator

“…The layer of the PEG-halide ions formed on the Cu surface can suppress Cu electrodeposition by physically obstructing the Cu ions from approaching the electrode surface, and its suppression ability depends on the type of halide ions. [30][31][32] It was reported that the suppression strength of PEG and halide ions was in the order of Cl -< Br -< Iat the same concentration of halide ions. 31 In this study, we adopted a considerably low concentration of PEG (5 μM) to obtain the suppression breakdown behavior by enhancing the effect of mass transport on the surface coverage of the suppression layers.…”

“…35,36,39 We previously reported that the suppression strength of PEG and TSV filling performance can be modulated by halide ions. 23,[30][31][32] The suppression effect increased in the order of Cl − < Br − < I -, and we speculated that Cland Brformed PEG-Clor PEG-Brlayers on the Cu surface, whereas Iformed CuI. Hence, we hypothesized that if the suppression strength can be enhanced by replacing Clwith Bror I -, then PEG-halide ion layers can potentially induce bottomup filling by establishing passive-active regions for Cu electrodeposition.…”

“…9,[26][27][28][29] Recently, iodide (I -) and bromide (Br -) ions have been demonstrated to function similarly as organic levelers, i.e., facilitating the bottom-up filling of Cu at TSVs and microvias. [30][31][32][33] Although the combination of a suppressor, an accelerator, and a leveler successfully induces Cu bottom-up filling at microscale features, the number of additives used in the Cu electrodeposition process must be reduced to facilitate maintenance of electrolyte performance, which can potentially extend the electrolyte lifetime.…”

A Review on the Fabrication and Reliability of Three-Dimensional Integration Technologies for Microelectronic Packaging: Through-Si-via and Solder Bumping Process

“…Kim et al [52] showed that by adding thiourea to the suppressor, PEG-PEG-SPS-I − , the filling time is halved. In addition, Sung et al [53] found out that the reduction in efficiency of the electroplating method occurs when unstable CuI exists at the suppressing layer. To prevent the formation of CuI, they replaced an iodine ion in PEG-PEG-SPS-I − to bromine ion and made PEG-PEG-SPS-Br − .…”

Superconformal Cobalt Electrodeposition with a Hydrogen Evolution Reaction Suppressing Additive

“…Many studies have been conducted on the behavior of additives and their growth mechanisms; however, various additives are still being developed for copper electrodeposition. [19][20][21][22][23][24] In the case of nickel, one of the iron group metals, there have also been many studies on additives for superconformal filling. Polyethyleneimine (PEI) and benzimidazole derivatives, such as 2-mercaptobenzimidazole (MBI) and 2-mercapto-5-benzimidazolesulfonic acid (MBIS), were shown to yield void-free feature filling.…”