Development of new concept thermoplastic temporary adhesive for 3D-IC integration

2.5D and 3D integration technology using temporary bonding has become main stream in the semiconductor industry in recent years. However, thermal stability, low damage, and low temperature debonding are still areas of challenge. Meanwhile, the demand for a solution has been rapidly increasing to enable the high volume manufacturing of 3D-IC products. In this paper, we report the development of a new type thermoplastic temporary adhesive. In general, thermoplastic material is considered difficult to overcome the critical issues that it faces during the back side processing in 3D-IC production due to its thermal behavior. In a previous study, the glass transition point (Tg) of adhesive was considered as a key parameter to improve thermal resistance. However, the high Tg material also induced large warpage from its internal stress, and had difficulty in obtaining sufficient coverage on high topography wafer surface. The latest adhesive by TOK provides solutions to those problems. The new thermoplastic adhesive, which has optimized rheological property and elastic modulus, can reduce warpage and maintain stability through thermal processes such as PECVD and solder reflow. In addition, it can reduce void issues found during PECVD passivation process. The new thermoplastic adhesive can also coat over 100 um in thickness with good total thickness variation (TTV) post bonding, which can be adapted to the C4 bump application. This study on adhesive was demonstrated with the thin wafer handling system by TOK called Zero Newton®. The temporary adhesive is compatible with both perforated and non-perforated glass carriers and is separated with each corresponding scheme. The adhesive is removed by solvent dissolving from the substrate, so low residue and damage are expected as a result. The details of this study on thermoplastic material and demonstration of wafer handling process are fully described in this report.