Simultaneous filling of through silicon vias (TSVs) with different aspect ratios using multi-step direct current density

Abstract

In this study, a multi-step current density method was investigated to fill TSVs with different aspect ratios (⌀20 µm × 120 µm, ⌀30 µm × 130 m, ⌀40 µm × 140 µm and ⌀50 µm × 150 µm) simultaneously without voids. First, the effects of current density and TSV size on the growth mode of electrodeposited Cu were investigated. The experimental results indicated that low current density (1 mA cm−2) was favorable to bottom-up filling for TSVs with small size (⌀20 µm × 120 µm). The medium current density of 6 mA cm−2 was favorable to bottom-up filling for the TSVs with large sizes (⌀40 µm × 140 µm and ⌀50 µm ×150 µm). The high current density of 9 mA cm−2 could only be used for bottom-up filling in the ⌀50 µm × 150 µm TSV. Second, three kinds of initial shape of Cu-TSV at the beginning of electroplating were proposed to discuss the growth mechanism of electrodeposited Cu in TSVs. Then, the effect of temperature on the filling mode of the TSVs was investigated. It was found that the deposition rate at different locations of the TSV sidewall was more uniform at low temperature, which was helpful to form the bottom-up filling mode. Finally, all the TSVs with different aspect ratios were simultaneously filled void free at 20 °C when the current densities of 3 and 6 mA cm−2 were applied for 90 min.