Diffusion and eutectic bonding are gaining broad acceptance in 3D integration and packaging. Many bonding schemes are based on copper because this material is used extensively in FEOL, has a well developed CMP history and high yield TSV's have been proven. One of the issues for low resistivity interconnects and high bonding yield is the surface cleaning methods used to remove copper oxidation. This paper will present the results of studies using DuPont EKC products for copper surface preparation prior to wafer bonding.
This paper will examine the combined use of both permanent and temporary high-temperature polyimide adhesives used to avoid thin wafer handling. While 3D-TSV technology can improve functionality and performance, adoption of this technology has been delayed by cracking as well as unwanted wafer bowing. This presentation shows means by which a photo-lithographic polyimide adhesive is used in a temporary bonding scheme to eliminate intermediate-stage thinned wafer handling.
This paper will examine the use of high temperature Polyimide temporary adhesives and advanced copper cleaning solutions for thin wafer handling during metal to metal (Cu-Cu) bonding. In the case of Cu to Cu solid state diffusion bonding, temperature requirements can be up to 400C for as long as 40 minutes. These extreme conditions pose a significant challenge with existing materials used for temporary bonding.
Polyimides are ideally suited for high temperature application and polyimide adhesives have been developed which can withstand 400°C processing without significant failure in adhesion. As well, Cu to Cu bonding processes will require the need for contamination free surfaces, which becomes increasingly important if lower temperature processes (<400C) are desired. Close-coupled copper cleaning immediately prior to the bonding step offers an excellent approach for providing process reproducibility while achieving increased electrical yields. Utilizing advanced wet cleaning solutions to obtain optimal Cu surface preparation through the removal of undesirable copper oxide layers as well as organic contaminants such as Benzotriazole (BTA) is also discussed in detail.
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