A review of wafer bonding materials and characterizations to enable wafer thinning, backside processing, and laser dicing

A wide range of adhesives and coatings has been reported to enable wafer bonding practices that support applications leading to 3-D packaging. These polymeric substances include rosin-urethane, silicone , rubber, and acrylic. In the case of a carrier bonded wafer, the material allows grinding and polishing to Lt20um, protection of the devices from backside processing such as through silicon vias (TSVs) and the associated cleans and metallization steps. In conjunction with laser dicing, the material must be removed from the wafer without residue detection. Proper characterization methods are used to model product qualification during fab integration. For example, thermal tests such as TGA and DSC, may be used to predict pre-processing conditions to improve on-wafer curing. Cleaning tests may utilize the extreme sensitivity and delicate contact of the mercury probe analyzer, which has been shown to rapidly characterize film residues at below 10 angstroms. Metrology tests include planarization, uniformity as total thickness variation (TTV), contour mapping, stress and/or bow as deviation from reference, and surface roughness. Although all of these measurements may tell a story about a pure material or a smooth wafer, they are especially interesting when their application is applied to model the process. This paper will describe a range of materials currently under evaluation and provide examples of characterization methods and models used to predict issues during integration.