Wafer Bonding Using Dielectric Polymer Thin Films in 3D Integration

Abstract

ABSTRACTA key process in our approach to monolithic three-dimensional (3D) integration is the bonding of 200-mm wafers using dielectric polymer thin films as bonding glues. After discussing the desired properties of polymer thin films, we describe how bonding protocols are evaluated using silicon and glass wafers. After bonding, the fraction of bonded area was inspected optically and a razor blade method was used to indicate bonding strength. Thermal stability and bonding integrity were evaluated using thermal cycling and backside grinding and polishing. To date, we have studied benzocyclobutene (BCB), Flare™, and methylsilsesquioxane (MSSQ) and Parylene-N as bonding glues. Wafer pairs bonded using BCB showed a larger fraction of bonded area, and those using Flare indicated higher thermal stability. Both BCB and Flare glues provided good bonding integrity after backside grinding tests. Changes in the chemical structures of BCB and Flare glue during bonding were analyzed using FTIR in order to understand the bonding mechanism and to improve the bonding process.