Adhesive Wafer Bonding Using Partially Cured Benzocyclobutene for Three-Dimensional Integration

Abstract

Wafer-level three-dimensional integration (3D) is an emerging technology to increase the performance and functionality of integrated circuits (ICs), with adhesive wafer bonding a key step in one of the attractive technology platforms. In such an application, the dielectric adhesive layer needs to be very uniform, and precise wafer-to-wafer alignment accuracy of the bonded wafers is required. In this paper we present a new adhesive wafer bonding process that involves partially curing (cross-linking) of the benzocyclobutene (BCB) coatings prior to bonding. The partially cured BCB layer essentially does not reflow during bonding, minimizing the impact of inhomogeneities in BCB reflow under compression and/or any shear forces at the bonding interface. The resultant nonuniformity of the BCB layer thickness after wafer bonding is less than 1% of the average layer thickness, and the wafers shift relative to each other during the wafer bonding process less than (average) for 200 mm diameter wafers. When bonding two silicon wafers using partially cured BCB, the critical adhesion energy is sufficiently high for subsequent IC processing.