Through Silicon Vias With Invar Metal Conductor for High-Temperature Applications

Through silicon vias (TSVs) are key enablers of 3-D integration technologies which, by vertically stacking andinterconnecting multiple chips, achieve higher performances,lower power, and a smaller footprint. Copper is the mostcommonly used conductor to fill TSVs; however, copper hasa high thermal expansion mismatch in relation to the siliconsubstrate. This mismatch results in a large accumulation ofthermomechanical stress when TSVs are exposed to high temperaturesand/or temperature cycles, potentially resulting in devicefailure. In this paper, we demonstrate 300 μm long, 7:1 aspectratio TSVs with Invar as a conductive material. The entireTSV structure can withstand at least 100 thermal cycles from −50 °C to 190 °C and at least 1 h at 365 °C, limited bythe experimental setup. This is possible thanks to matchingcoefficients of thermal expansion of the Invar via conductor andof silicon substrate. This results in thermomechanical stressesthat are one order of magnitude smaller compared to copperTSV structures with identical geometries, according to finiteelement modeling. Our TSV structures are thus a promisingapproach enabling 2.5-D and 3-D integration platforms for hightemperatureand harsh-environment applications.