A wet chemistry approach to sub-micron,removable flip chip interconnects

摘要

Higher performance is the main driver in the integrated circuit (IC) market, but along with added function comes the costof increased input/output connections and larger die sizes. Space saving approaches aimed at solving these challengesincludes two technologies; 3D stacking (3D-ICs) and flip chip assemblies. Emerging ICs require sub-micron scaleinterconnects which include vias for 3D-ICs and bump bonds for flip chips. Photolithographic techniques are commonlyused to prepare templates followed by metal vapor deposition to create flip chip bump bonds. Both the lithography stepand the metal properties required for bump bonding contribute to limiting this approach to a minimum bump size of 10 m. Here, we present a wet chemistry approach to fabricating uniform bump bonds of tunable size and height down tothe nanoscale. Nanosphere lithography (NSL), a "soft" lithographic technique, is used to create a bump bond template ormask for nanoscale bumps. Electrochemical deposition is also used through photoresist templates to create uniformbump bonds across large area wafers or dies. This template approach affords bumps with tunable diameters from 100s ofnanometers to microns (allowing for tunable interconnect pitch and via diameters) while the use of constant currentelectoplating gives uniform bump height over large areas (>1 cm2).