A Novel Photosensitive Permanent Bonding Material for Polymer/Metal Hybrid Bonding

Wafer-level hybrid bonding techniques, which provide simultaneous bonding between metal-metal and between dielectric-dielectric layers, has attracted more attention in recent years for fabricating 3D integrated circuits with high bandwidth and high interconnect density. However, there are some issues for conventional hybrid bonding using silicon oxide as the dielectric, such as the high stress and low tolerance to height difference of bonding interface, which limits its applications for 3D heterogeneous integration.

In this paper, a novel negative-tone photosensitive polymeric bonding material is proposed to be used as a dielectric to enable polymer/metal hybrid bonding. Compared to silicon oxide, the polymeric material with low Young’s modules is able to absorb thermally induced stress created during bonding process and results in lower bow for the bonded substrates. The key features for the photosensitive permanent bonding material include 1) low dielectric constant and dissipation factor; 2) superior thermal stability (>350°C); 3) excellent fine-pitch capability (4 micron); and 4) low processing and curing temperatures (<200°C). The photosensitive permanent bonding material has also been demonstrated to be able to be patterned and bonded to another Si or glass substrate with good adhesion and no obvious defects. The details of the material characterization, process optimization, reliability, and preliminary polymer/metal hybrid bonding results will be presented in the paper.