Wafer-level hybrid copper/polymer bonding technology suitable for wafer-level 3D integration (called “thinning after bonding”) was developed. A damascene process is applied for fabricating copper pads. After chemical mechanical polishing (CMP), a globally flat bonding surface is obtained by co-planarization of copper and polymer during barrier CMP. The key to this co-planarization process is optimizing polymer polishing rate by changing polymer cure temperature. As a result of this optimization, copper-copper bonding was achieved, and a seamless polymer-polymer interface was produced. Moreover, a model for local-deformation at the polymer-polymer interface is proposed. This model suggests that the adhesion strength of the bonded polymers is determined by the contact-area ratio of the polymers under thermocompression.
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