An optimized through-via bottom-up method for simultaneous-filling TSVS of different aspect-ratios and its potential application on high-frequency passive interposer

Abstract

Passive interposer has become an attractive integrator for 2.5D/3D integration. TSV is the key technology for passive interposer. Coaxial-like transmission structure provides a low-cost solution of shielding TSV for high frequency application. Impedance matching needs coaxial-like TSVs to usually have different diameters. This paper presents an optimized through-via bottom-up filling method, which enables simultaneously copper filling TSVs with different aspect ratios. The demonstrated coaxial-like TSV structure have one signal-TSV and six grounded-TSVs. A potential voids problem of the filling method is identified and solved by adding suppressor. Simultaneously filling of signal-TSV and grounded-TSVs was realized by adjusting electroplating parameters, e.g. current density and stirring rate. The measured result of fabricated coaxial-like TSVs is comparable to the simulation. The result verifies that with this optimized filling method, the design of passive interposer equipped with coaxial-like vias can be more flexible and the impedance matching between TSVs and other components can be easily realized for high frequency applications.