Comparison of temporary bonding and debonding process flows
The demands on temporary wafer bonding materials used for the fabrication of 3D integrated circuits (ICs) are rigorous. As compared to the waxes and tapes that are used for the thinning of wafers only, temporary wafer bonding systems must support the wafers through thinning plus be compatible with many fabrication processes (such as vacuum depositions, lithography, metal etches, solvent cleans, polymer cures) while maintaining adhesion and providing mechanical support to the wafer. Then the materials must quickly and cleanly debond without damage to the thin device layers. Because of these challenging requirements, a great deal of study must be done when selecting the temporary bond material(s) for a given 3D fabrication process. While many different systems have recently been developed, each material set has limitations and trade-offs that must be understood by the process design team. As a result, many companies and research institutions have undertaken to independently compare the performance of temporary wafer bonding systems through common fabrication steps in a 3D integration process. These studies are in addition to the work thta has been done by the material suppliers and equipment vendors. See Chapters 10-13 by SUSS, EVG, TOK, 3M for descriptions on their available processes. Chapter 9 discusses the general materials properties requirements for temporary bonding adhesives. Although carrierless designs for thin wafer handling have been reported , most thin wafer handling solutions are wafer support systems (WSSs) where the wafer to be thinned is temporarily bonded on a supporting wafer with an adhesive.