| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 98 === The development of science and technology continuously progresses. Electronic components increasingly become small, thin, short and light. The evolution of semiconductor technology has reached a point where the packaging now plays an important role in the overall performance of the IC devices. There are some bottlenecks of two-dimensional (2D) packaging, which include size, speed, and volume of electronic packages. 3D packaging technology not only change horizontal interconnect techniques to vertical ones but also increase counts of input and output (I/O). Thus, 3D technology will replace 2D technology in the future.
Many articles have reported different plating formulas that are capable of forming superfilling. However, the top surface profile of the copper deposit inside the TSV always is V-shaped. According to our research, different top surface profiles of the copper deposits inside the TSV might cause different filling results. If the top surface profile of the copper deposit inside the TSV is V-shaped it has a risk to form a seam or a small void in the filled TSV. Another plating process will form a U-shaped profile at the top of the TSVs during plating, the plating process can make sure of no void and seam formation during plating. This paper is focused on development of a novel copper electroplating formula for filling TSV and this formula can lead to the top surface profile of the copper deposit inside the TSV to be U-shaped.
In this study, filling performance of the novel plating formula was evaluated by examining cross-section of the filled TSVs using an optical microscope (OM). The effects of chemical and physical interactions between the plating additives and fluid dynamics were characterized by using a potentiostat with a three-electrode cell. We used two rotation speeds of working electrode (WE) to simulate the fluid motion around the wafer. One was fixed at 1000 rpm to simulate the fluid motion outside the TSV. The other was fixed at 100 rpm to simulate the fluid motion inside the TSV. Electrochemical analyses show that the filling mechanism obey a model of convection-dependent adsorption (CDA) behavior.
The U-shape copper plating formula led to the bottom-up behavior looking like the motion of an elevator. That is, the top surface profile of the copper deposit filled in the TSV always was a flat plane during plating. Besides, the sidewall shrinkage due to copper deposition was insignificant during plating. This filling behavior is totally different from that of a conventional copper plating formula for via filling, which usually behaves a zipper-type filling mode and thus causes a seam formation at the center of the filled TSV. This invention of this work can make sure of no void and seam in the filled TSV with an aspect ratio of 3.5, where the diameter is 20 μm and the depth is 70 μm. Thus, the reliability of the TSV can be greatly improved. According to the plating results, we considered that the suppressor is the key point to improve yield. In our research, different suppressors might cause different filling results. After we tried using PAA to replace PEG, the new formula could filling high aspect-ratio vias but the plating results were not uniform. Finally, both yield and the capability of filling high aspect-ratio vias had improved after we tried using the suppressors of PEG(400) and PAA.
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