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

Abstract

Wafer-level three-dimensional integration ͑3D͒ is an emerging technology to increase the performance and functionality of integrated circuits ͑ICs͒, 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 ͑ϳ1 m͒ of the bonded wafers is required. In this paper we present a new adhesive wafer bonding process that involves partially curing ͑cross-linking͒ of the benzocyclobutene ͑BCB͒ 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 1 m ͑average͒ for 200 mm diameter wafers. When bonding two silicon wafers using partially cured BCB, the critical adhesion energy is sufficiently high ͑ജ14 J/m 2 ͒ for subsequent IC processing.

III‐V/silicon photonics for on‐chip and intra‐chip optical interconnects

“…Structured silicon wafers were bonded both to unpatterned silicon wafers and Pyrex wafers. Many other papers report on the excellent properties (bonding strength, residual stress, bonding quality) of DVS-BCB bonding [34][35][36].…”

“…Attachment is done at 150°C, as DVS-BCB has about the lowest viscosity at this temperature [36] and keeping the DVS-BCB at this temperature does not significantly increase the degree of polymerization for at least an hour (see Fig. 9).…”

Heterogeneous integration for optical MEMS

“…Via-last heterogeneous integration processes based on adhesive wafer bonding [3,4] have been implemented for a number of MOEMS and MEMS devices, including infrared bolometer arrays [5,6], mono-crystalline silicon micro-mirror arrays [7][8][9] and radio frequency meta-material surfaces [10]. Fig.…”

Three‐Dimensional (3D) Integration

“…Further work using BCB as a bonding layer has focused on partially curing the BCB film prior to bonding [51,[76][77][78]. A number of advantages have presented themselves in using partially cured BCB: reduced bonding-induced misalignment [78], mechanical rigidity requisite for copper damascene patterning [76], and enough free bonds at the surface to continue to produce strong bonding [51].…”