Advances on Fabrication and Application of Through Silicon Via for Radio Frequency Circuits

• Author / Creator

  Qiu, Yang

• Through silicon via (TSV) has been considered as an astonishing milestone in the evolution of three-dimensional integrated circuit (3D IC), because of its exclusive and pivotal function of providing signal exchanging paths in the horizontal direction to stacked layers efficiently. Unfortunately, Cu (copper) electroplating, the most popular TSV metallization technique, is still not ideal; and the interfacial quality of silicon interposer, i.e. multiple layers of TSVs, is still problematic, which will not only result in device dysfunction but also prohibit its wide spread to other areas. In this thesis, based on the comparison of advantages and disadvantages of newly emerged alternatives to Cu electroplating, an optimal mechanism which is the vacuum suction of Ag (silver)-based conductive polymer is proposed to achieve the easy, rapid, void-free and low cost TSV metallization. To better understand the vacuum suction process, a variety of vacuum conditions in terms of pressure differences (from 0 to 2 kPa) and durations (1 s, 2 s and 3 s) are tested. It is found that increasing the vacuum level is more effective than extending the vacuum time to produce a higher filling ratio. To fully fill the through vias with diameter of 100 µm and depth of 500 µm, at least 1.6 kPa and 3 s is needed. The volume resistance of fully filled TSVs is measured by running the typical two-point probe test twice and the result indicates the average resistance is lower than 25 Ω. Also, during the temperature increase from 20 °C to 120 °C, the resistance variation is less than 5 %, which implies that their thermal resistance stability is acceptable.Moreover, through the replacement of conventional redistribution layer (RDL) formed on the chip surface with conductive polymer metallized trenches embedded in the chip body, a new silicon interposer architecture is built, whose fabrication process is simplified and interfacial connection becomes homogeneous and more dependable. More critical parameters including via dimension, conductivity and viscosity are investigated in various vacuum conditions. The filling depth measurement shows that either enlarging the via opening or lowering the conductive polymer’s viscosity would be beneficial to the filling process. The resistance characterization result suggests that the C(carbon)-based conductive polymer is not suitable for the TSV metallization as the average resistance of relevant channels is higher than 20 kΩ.Lastly, the idea that through via structures can be more efficiently metallized through the vacuum suction of conductive polymer, is applied to the development of substrate integrated waveguide (SIW). Through the proper manipulation of the vacuum condition, the metallization level (i.e. filling ratio) of the through via structure becomes rather adjustable; based on which, two prototypes of band-stop SIW filter with partial height via resonator are fabricated in a standard commercial rigid substrate (RO4003C) and a self-made flexible substrate of Polydimethylsiloxane (PDMS) respectively. For the rigid SIW filter, the measured resonant frequency and maximum reflection coefficient are 10.25 GHz and -1.6 dB, which are enough to prove the accuracy of this SIW fabrication method, considering the simulated results are 10.5 GHz and -1 dB. For the flexible SIW filter, relatively good agreements between the measurement (14.6 GHz and -2.3 dB) and the simulation (15 GHz and -1 dB) can also be obtained; in addition, only the resonant frequency is influenced by the bending, as it shifts to 14 GHz and 13 GHz when the bend radius reduces to 35 mm and 12.5 mm respectively.

• Subjects / Keywords

  • Radio Frequency
  • Filter
  • Substrate Integrated Waveguide
  • Silicon Interposer
  • Through Silicon Via
  • Conductive Polymer

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-4fmw-9s16

• License

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