Observation of Bis-(3-sulfopropyl) Disulfide (SPS) Breakdown at the Cu Cathode and Insoluble Anode under Open-Circuit, Unpowered Closed-Circuit, and Electrolysis Conditions

Abstract

Understanding additive breakdowns under operating conditions is highly needed for designing robust, high-efficiency Cu electroplating systems. In this study, the decomposition of bis-(3-sulfopropyl) disulfide (SPS) was examined in the membrane electroplating cell where the cathode and anode are separated. With an open circuit, the SPS was split into Cu(I)MPS − at the cathode via the chemical reaction with Cu + , followed by oxidation to 1,3-propane disulfonate (PDS). No chemical reactions take place at the insoluble anode. With an unpowered closed-circuit, SPS at the cathode and the insoluble anode were simultaneously broken down at an equal rate because of the formation of Cu + at the anode by a galvanic proportionate reaction. With current flowing, SPS in the catholyte was consumed via the reaction with Cu + as well as by incorporation, while that in the anolyte was decomposed via anodic oxidation.

Influence of Reducing Agent on Chemical Decomposition of Bis(3- sulfopropyl) Disulfide (SPS) in Cu Plating Bath

“…3-9). 27 As shown in Fig. 9, the SPS concentration was checked during aging under the open-circuit condition for 3 d in the absence of O 2 .…”

“…A Cu plate (area: 25 cm 2 ) was used as a source of Cu + , which initiated SPS decomposition. 27 Reducing agents, namely, NaPO 2 H 2 , HCHO, OCHCO 2 H, N 2 H 4 , and (COOH) 2 with concentrations of 100 μM (low concentration) and 10 mM (high concentration) were used. The system was left to react for 10 h, and the solution was sampled every 2 h. The electrolyte was stirred using a magnetic stirring bar at 300 rpm at room temperature (25 °C).…”

“…[17][18][19][20][21][22][23][24] The organic additives are not stable in the Cu electrolyte, and they gradually degrade via various reactions. [25][26][27][28][29][30][31][32][33][34][35] In particular, SPS, a commercial additive that acts as an accelerator, decomposes faster than suppressors and levelers. SPS has two major decomposition mechanisms in Cu electroplating; it rapidly breaks down to form 1,3-propane disulfonic acid (PDS) by a direct electrochemical reaction (Eq.…”