Physical Properties of Deposits and Three-Dimensional Structures Prepared By High-Speed Electrolytic Copper Plating Using a Jet Flow Device
Authors: Suzuki Yohei , Cordonier Christpher E.J. , Umeda Yasushi , Honma Hideo , Takai Osamu , Noh Joohyong 
Published: February 2020

Since copper has excellent properties such as malleability and conductivity, it is widely used in the electronics field. Copper sulfate plating is expanding further in fields requiring thick deposits such as for heat dissipation boards and bumps for stress relaxation during semiconductor mounting. In order to improve productivity and reduce cost, high speed electroplating using high current density is desired. However, in electroplating under high current density, abnormal deposition such as burnt deposits and dendrites due to insufficient supply of the metal ion. In order to facilitate the supply of the metal ion, our group focused on mechanical agitation type jet devices rather than conventional air or paddle agitation. In this study, the physical properties of deposits prepared by conventional copper sulfate plating at 5 A/dm2 and the high speed copper plating at 30 or 50 A/dm2 were compared. Furthermore, the high-speed copper sulfate plating method was applied to wiring and bump resist patterns where production of three-dimensional structures was demonstrated.

20×30 mm cut copper plates were used as the test substrate, which were treated with the alkaline degreasing and the acid activation prior to plating. Three kinds of additives Bis-(3-sulfopropyl) disulﬁde (SPS), Janus Green B (JGB) and Polyethelene glycol-20000 (PEG-20000) were used in the copper sulfate plating solution. Samples were annealed at 120°C for 60 min after plating. Investigation of physical properties was conducted by comparison of crystal orientation measured by X-ray diffraction (XRD) and electrical conductivity measured by sheet resistance. Furthermore, the etching rate of each film was calculated from the mass loss per unit etching time.

The additives were optimized for preparation of the three-dimensional structures. The current density was swept at an arbitrary speed from 0 A/dm2 to a target current density, and once reached, the current density was maintained until the target film thickness was obtained. The test substrate after plating was subjected to resist observation and then to observation using a scanning electron microscope (SEM).

Fig. 1 shows the crystal orientation attained at each current density. It was confirmed that both films produced at the current densities of 30 and 50 A/dm2 by high speed copper plating and the film produced at 5 A/dm2 using the conventional method were oriented with 60% of the 111 crystal phase. The sheet resistance values of all three films exhibited approximately the same value of 0.93 to 0.95 Ω/sq. . On the other hand, the etching rate of the films produced by high-speed copper plating were 2.5 µm/min, whereas that of the film produced by the conventional method was 1.7µm/min. Fig. 2 shows the wiring pattern filled with 30 A/dm2. It was confirmed that pattern filling by high speed plating can be accomplished 10 times faster than with the conventional method. Resist pattern filling by plating at higher current density will be discussed in detail.

The high-speed copper plating film using a jet flow device has the near physical properties as the conventional method. Furthermore, since filling of the pattern substrate can be performed in a short time, it is considered that it can contribute to improvement of productivity in the electronic field.

Figure 1