Optical connectivity has the potential to outperform copper-based TSVs in terms of bandwidth at the cost of more complexity due to the required electro-optical and opto-electrical conversion. The continuously increasing demand for higher bandwidth pushes the breakeven point for a profitable operation to shorter distances. To integrate an optical communication network in a 3D-chip-stack optical through-silicon vertical VIAs (TSV) are required. While the necessary effort for the electrical/optical and vice versa conversion makes it hard to envision an on-chip optical interconnect, a chip-to-chip optical link appears practicable. In general, the interposer offers the potential advantage to realize electro-optical transceivers on affordable expense by specific, but not necessarily CMOS technology. We investigated the realization and characterization of optical interconnects as a polymer based waveguide in high aspect ratio (HAR) TSVs proved on waferlevel.

To guide the optical field inside a TSV as optical-waveguide or fiber, its core has to have a higher refractive index than the surrounding material. Comparing different material / technology options it turned out that thermal grown silicon dioxide (SiO₂) is a perfect candidate for the cladding (n_SiO2 = 1.4525 at 850 nm). In combination with SiO₂ as the adjacent polymer layer, the negative resist SU-8 is very well suited as waveguide material (n_SU-8 = 1.56) for the core. Here, we present the fabrication of an optical polymer based multimode waveguide in TSVs proved on waferlevel using SU-8 as core and SiO₂ as cladding. The process resulted in a defect-free filling of waveguide TSVs with SU-8 core and SiO₂ cladding up to aspect ratio (AR) 20:1 and losses less than 3 dB.

Date Published: 16 May 2017
PDF: 9 pages
Proc. SPIE 10232, Micro-structured and Specialty Optical Fibres V, 102320T (16 May 2017); doi: 10.1117/12.2265168

Published in SPIE Proceedings Vol. 10232:
Micro-structured and Specialty Optical Fibres V
Kyriacos Kalli; Jiri Kanka; Alexis Mendez; Pavel Peterka, Editor(s)