Temporary and Permanent Adhesives for Thin Wafer Handling and Assembly

Temporary wafer bonding has emerged as the method of choice for handling silicon wafers during the thinning and high-temperature backside processing required for the manufacture of 3D device structures. Among the requirements for temporary wafer bonding materials to be used in high volume manufacturing are simple device and carrier wafer preparation, high-throughput wafer bonding, excellent thermal stability, and clean room-temperature release directly from the device wafer. We will present successful temporary wafer bonding using a new BCB (benzocyclobutene)-based material that can meet these requirements. For this temporary wafer bonding technology, wafer preparation involves spin coating the device wafer with the BCB-based adhesive to a thickness of up to 100 μm and spin coating the carrier wafer with an adhesion promoter. The wafers can then be bonded at temperatures as low as 80 °C for as short as 30 seconds. The low bonding temperature means the wafers can be loaded into a preheated wafer bonding tool, eliminating the time needed to heat and cool the bonding chucks during the bonding cycle. Also, no curing of the material is required during the bonding, enabling a short process time and high wafer throughput. Curing of the adhesive is done as a batch oven cure at 210 °C for one hour after which the material is stable enough for backside processes up to 300 °C. The material has been designed to adhere well to the carrier wafer and debond directly from the device wafer without any chemical or radiation pretreatment, leaving a clean device wafer surface in need of only mild cleaning before further processing.