Fabrication and testing of through-silicon vias used in three-dimensional integration

Abstract

The formation of through-silicon vias (TSVs) provides a vertical interconnect scheme that can be used in three-dimensional stacking technologies. A sloped via sidewall is essential for conformal coverage of via lining materials deposited in subsequent steps that provide insulation (SiO2), barrier (TaN), and metal seed (Cu) layers. In this article, via sidewall angles in the range of 83°–90° are investigated resulting in variable degrees of conformal lining of the insulation, barrier, and seed layers. Via insulation is deposited by plasma enhanced chemical vapor deposition, while barrier and seed layers are deposited by sputtering. A modified Bosch process, using a deep reactive ion etch tool, allows formation of differing via profiles in silicon substrates. Cross-sectional views of via profiles showing the coverage of lining materials (SiO2, TaN, and Cu) are examined with a scanning electron microscope. For a constant via sidewall angle, variable aspect ratios allow us to determine the specific via profile that can be conformally lined and filled by Cu electroplating without the presence of voids. The aspect ratios of the vias under study are in the range of 2–4. Electrical performance of the fabricated TSVs is reported and is consistent with expected performance.