A UV-curing Temporary Bonding Material with High-temperature Survivability

Puzzled by the fracture and warpage issues of ultra-thinning wafer, temporary bonding and de-bonding (TBDB) technology emerges as the time requires. Despite that temporary bonding material (TBM) with thermosetting structure possesses excellent thermal mechanical resistance at high temperature, it brings a great challenge in cleaning process after de-bonding due to the complex cross-linked network. It is thus developing a TBM that is easy to clean and simultaneously maintains high thermal stability is a popular and challenging task. Herein, several UV-curing TBM were synthesized with the function group (FG) content being controlled in a broad range. The curing reaction can be achieved by UV irradiation within 30 s according to the photo-DSC measurements, showing its great advantages on cost, energy saving, efficiency, and environmental protection. Moreover, since it can be cured reaction at room temperature, greatly reducing potential for warpage in the pair of wafers. The thermal resistance was evaluating by TGA test, and the results showed that only at a higher FG content, it could exhibit superior thermal stability (Td,5% > 420 °C). And the bond strength was highly corresponded to the FG content. The average film thickness is measured to be 30.75 μm and TTV (total thickness variation) is merely 0.36 μm. Subsequently, a range of posterior processes were assessed, encompassing thinning, chemical mechanical polishing (CMP), and PVD, among others. Fortunately, the bonding pair successfully passed these tests without any voids or deflects by scanning acoustic microscopy (SAM), and simultaneously the device wafer was successfully reduced to the expected thickness of 150 μm. Thanks to the appropriate adhesion, the pair of ultra-thin wafers could be effortlessly separated through mechanical means at ambient temperature. For cleaning, there were two approaches available. When the film is thick enough (> 60 μm), it could be directly peeled off from the device wafer due to its robust mechanical properties. Otherwise, it was required to remove with a commercial cleaning agent. Anyhow, both have achieved the cleaning effect according to the X-ray spectroscopy (EDS) results.