Self-alignment structures for heterogeneous 3D integration

A novel self-alignment technology, called positive self-alignment structures (PSAS), for heterogeneous 3D integration is described. Using a set of precisely reflowed photoresist structures in conjunction with the corresponding inverse pyramid pits, we demonstrate that submicron alignment can be achieved without an advanced placement tool. The positive self-alignment structure technology is fabricated on top of electronics or devices, and as a result, it does not take up additional electronic real estate, and it can be fabricated on any surface, including glass. This enables heterogeneous integration that involves non-silicon substrates, and at the same time simplifies the stacking of three or more chips. This paper describes the self-alignment mechanism, the fabrication of positive self-alignment structures (PSAS), and the test structures to measure the accuracy of alignment; the resulting misalignment on various substrates including glass and unpolished silicon surfaces are reported. In addition, the stacking of five chips is demonstrated and the resulting misalignment at each of the chip-to-chip interfaces is measured and reported.