BISTs for post-bond test and electrical analysis of high density 3D interconnect defects

Abstract

Cu-Cu hybrid bonding offers very high density interconnects (pitch around 2 μm or less) in 3D stacking integrated circuits (HD 3D-IC), but the smaller the Cu pad size, the more the fabrication and bonding defects have an important impact on yield and performance. Defects such as bonding misalignment, micro-voids and contact defects at the copper surface, can affect the electrical characteristics and the life time of 3D-IC considerably. In this paper, we propose two complementary test and characterization structures dedicated to high density 3D-IC interconnects. The first test structure permits to measure the misalignment defect with a great accuracy and the second to measure the RC delay of a periodic signal applied to a daisy chain composed of 3D Cu-Cu interconnects. The measured misalignment values and propagation delays allows to detect Cu-Cu full open, misalignment, and micro-voids, in order to assess performance of high density 3D Integrated Circuit. Both test structures are implemented as BIST engines, which are integrated and controlled with IEEE 1687, for an overall negligible area cost.