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Characterization and Application of a Novel Permanent Bonding Material
Due to the flowability of benzocyclobutene (BCB) and the unavoidable shear components of the bonding force applied by bonding facilities, it is quite challenging to achieve void-free BCB adhesive bonding with simultaneous high post-bonding alignment accuracy. To solve this problem, this paper reports a compensation method for alignment errors to achieve simultaneous void-free and accurate wafer bonding using soft-baked BCB. By characterizing the wafer shift induced bonding force, it is found that the wafer shift is a systematic error associate with the bonders but independent of the wafers. Upon this investigation, a compensation method presetting a pre-bonding alignment shift opposite to the post-bonding shift is proposed to compensate the bonding induced wafer shift. Using this method, void-free bonding with soft-baked BCB has been achieved, and the alignment errors are improved significantly from around 35–40 μm to around 3 μm. Test results show that the average bonding strength of soft-baked BCB is about 26.4 % higher than that of partially-cured BCB. The preliminary results demonstrate the efficacy of the proposed compensation method, which has potential to improve the alignment accuracy of BCB bonding for three-dimensional integration, MEMS, and microsensors.
There can be two kinds of de-bonding options in the aspect of the releasing interface, one is carrier release and the other is device wafer release. Thermoplastic adhesives are used in most cases for carrier release because the materials can easily be cleaned by solvent. On the other hand, device wafer release is usually selected for thermoset adhesives, which is difficult to remove by solvent.
Wafer bonding with intermediate polymer adhesives is an important fabrication technique for advanced microelectronic and microelectromechanical systems, such as three-dimensional integrated circuits, advanced packaging, and microfluidics. In adhesive wafer bonding, the polymer adhesive bears the forces involved to hold the surfaces together. The main advantages of adhesive wafer bonding include the insensitivity to surface topography, the low bonding temperatures, the compatibility with standard integrated circuit wafer processing, and the ability to join different types of wafers. Compared to alternative wafer bonding techniques, adhesive wafer bonding is simple, robust, and low cost. This article reviews the state-of-the-art polymer adhesive wafer bonding technologies, materials, and applications.
Permanent polymer bonding for MEMS device fabrication and packaging applications
- T C Eks Lim
- Seng