Semiconductor wafer bonding is an important process in IC packaging in many areas. These include:
micro-optics, traditional IC packaging, sensor packaging, temporary wafer bonding (processing of thin wafers, thin films transfer), Lab-on-Chip system (laboratory on a chip), microfluidics. There are the following requirements for adhesive wafer bonding: environment conditions (vacuum/air/inert gas), bonding layer between the wafers like thickness/width of the adhesive layer, total thickness variation (Total Thickness Variation, TTV), wafer alignment precision (up to ±1 µm), fast and efficient adhesive curing. The wafer level bonding process can be quite simple, but to achieve good results quality materials and wafer bonding equipment must be used. It is difficult to achieve high-precision alignment when using multiple adhesives. The problems are due to the fact that the adhesive acts as a lubricant between the wafers and interferes with their alignment due to capillary forces. Equipment manufacturers suggest two steps: first, the wafers are aligned on traditional alignment and exposure machines using specialized tools; then the plates are transferred to the bonding unit where they areconnected with clamping force after a heating cycle. In many cases high alignment accuracy is lost between wafer heating and bonding cycles and the operator cannot detect the problem,
until the wafer bonding is complete.