The Study of Dissolved Oxygen Control in TSV Electroplating Deposition
In TSV, it is one of the important techniques to fill the hole without defect as a conductive material .
The copper (Cu) is commonly used as a filling material because Cu has good electrical conductivity and excellent signal transfer characteristic in the GHz band.
The electroplating (EP) is widely used for proper filling way due to its fast speed and low cost. .
In TSV EP, as the aspect ratio of the TSV filling is increased, it is a also critical issue to maintain fast and constant bottom-up filling rate without void.
In this study, the relationship between the bottom-up rate of TSV EP and key process parameters was analyzed. In particular, we focused on the dissolved oxygen (DO) in the electrolyte and experimented the relationship between bottom-up filling rate and DO.
Fig.1 shows the bottom-up filling rate as functions of a VMS additive "A", "S" and the DO concentration. In Fig. 1, the effect of the DO concentration is more sensitive than other additives in view of the filling rate.
Equ.1 describes Fig.1
Equ.1 shows the additive oxygen present in the VMS which reacts with Accelerator Acc. As a result, the amount of Acc. is reduced. DO concentration control the oxidation-reduction reaction in EP Process which results in the reduced Bottom-up Rate. [3,4].
Fig.2 shows the simplified picture of the degasser mounted on the VMS supply line where the gas molecules dissolved in the VMS are removed by vacuum. Consequently, the concentration of DO can be lowered.
Fig.3 shows the TSV filling images as functions of the device type and DO concentration. As shown in Fig. 3, the stable characteristics of TSV filling are developed by keeping the DO concentration less than 1.0ppm.
In this paper, we investigated the relationship between TSV bottom-up rates and DO concentration. From experimental results, we found that it is essential to keep the DO concentration less than 1ppm. We installed degasser for the VMS in order to obtain a constant low DO concentration. As a result, we were able to achieve the stable TSV bottom-up rate and yield improvement.