Multiple dry film adhesive tapes are available for temporary bonding. Dry film adhesive tapes usually consist of a backing foil with adhesive films plus protective liners on both sides. Both adhesive films are debondable, but different debonding mechanisms are used for either side. This allows controlled debonding, where the separation between thin device wafer and carrier wafer happens at the interface between device wafer and tape. Next the tape is peeled off the carrier wafer, which enables recycling of the carriers.
Figure 1 shows the process flow for carrier wafer processing as it is implemented on the EVG820 lamination system. The tape is usually supplied in rolls, but optionally sheet feeding can be applied. First the dry film adhesive tape, supplied to the system on a reel-to-reel basis, is punched out according to the specified geometry. The protective film on the bottomside of the tape is peeled off. Then the tape is aligned to the carrier wafer either by mechanical or optical alignment. The tape is laminated with a controlled process, which avoids gas encapsulation in the interface. Finally the protective film on the topside of the tape is peeled off. The carrier with the laminated adhesive tape is now ready for the temporary bonding process.
Advantages of tape punching compared to the cutting technologies (laser and blade cutting) are better edge quality for minimum interference with the bonding and back-grinding process, no carrier edge degradation through cutting blades, almost no wear of the punching module components (punch and die-plate) and more flexibility in tape dimension and shapes. In case that edge trimming of the device wafer is being used, a reduced tape diameter can be used in order that no openly exposed tape interferes with backside processes after thinning. The wafer notch is punched out simultaneously, which enables full support of the thin wafer in the notch area, while avoiding openly exposed tape around the notch (Figure 2).
Figure 3 shows the debonding process flow for thin wafers temporarily bonded with thermal release adhesive tape or UV-release adhesive tape as implemented on the EVG850DBL automated debonding system for tapes. First the wafers are mounted on dicing tape on a film frame (US patent 6,792,991 B2). The carrier wafer gets debonded by either thermal or UV exposure. A cleaning step of the device wafer on film frame is optionally integrated. The adhesive tape is peeled off from the carrier. The carrier can be reused.
Figure 1: Schematic process flow for temporary bonding dry film lamination
Figure 2: The tape punching process enables tailored tape geometry according to the notch specification. The tape alignment ensures concentric lamination of the tape onto the carrier. Aligned lamination enables full support of the thin wafer in the notch area, while avoiding openly exposed tape around the notch.
Figure 3: Debonding process flow for thin wafers temporarily bonded with thermal release tape or UV-release tape as implemented on the EVG850DBL automated debonding system for tapes (US patent 6,792,991 B2)