Electrochemical simulation of electrodeposition growth of copper in Through Silicon Via(TSV)

Through silicon via (TSV) technology has the advantages of improving chip integration density, reducing package size, reducing transmission delay and realizing low power consumption. It is a key advanced technology to promote the development of chip packaging in three-dimensional direction. Electrodeposited copper is the main way to achieve interconnection in TSV because copper has the advantages of high conductivity and low cost. However, due to the small diameter of the silicon via and high aspect ratio, bottom voids, cavities or gaps may appear in the process of electrodeposition of copper, which seriously affect the electrical, thermal and mechanical properties of TSV. There are many factors affecting TSV electrodeposition, including the composition of electroplating solution, the size of TSV, the state of electrode surface, the pretreatment technology, type and concentration of additives, etc. Finite element analysis (FEA) could be an important method to understand the detail process and mechanism of the electrodeposition growth of copper, helping to realize the defect-free filling of TSV and ensure its application reliability in experiment. In this paper, the electrodeposition growth process of copper and its mechanism are analyzed in detail by electrochemical simulation and Tertiary current distribution theory. In the absence of any additives, TSV tend to preferentially seal at the orifice position, which hinders mass transfer of Cu2+ and leads to defects such as voids in TSV. We further studied the effects of material, structural and technological factors on the growth process of copper deposition, focusing on Cu2+ concentration, different via sizes with same aspect ratio of 10:1 and external electrode potential in constant mode. Firstly, we found that the Cu2+ concentration directly determines the growth rate of copper in TSV, and increasing the concentration of Cu2+ in electroplating solution help to the relatively uniform growth of copper in TSV, also improve the growth rate of copper. Secondly, increasing electrode potential will increase the growth rate of copper, but aggravate the non-uniform growth trend of copper at the same time. Thirdly, contrary to common sense, when the aspect ratio is fixed, the smaller the via size, the more uniform the electrodeposition growth of copper in TSV. Based on the above simulation results, we understand the main material, structural and process factors that affect the growth uniformity and speed of copper in TSV. The effects of various additives on electrodeposition of copper are also discussed.