Thin wafer processing is a key technology for 3D-ICs as it enables safe and reliable processing of thin wafer on front- and backside. Temporary wafer bonding to a carrier enables the reduction of cost-of-ownership of Through Silicon Vias (TSVs) manufacturing for several reasons. Reduced wafer thickness enables reduced aspect ratios of the vias, which results in shorter cycle times and less cost for via etching and plating. In addition the silicon real estate consumption for the TSVs is reduced, because a thinner wafer enables smaller via diameters.
For the introduction of a new manufacturing technology like thin wafer handling another important milestone is a versatile supply chain. Many semiconductor manufacturers have a multiple source policy for all materials in the fab. EV Group provides the EVG® ZoneBOND® Open Platform. Our customers get complete freedom of choice in regards to the temporary adhesive. Any type of adhesive from any supplier can be used. Thereby ZoneBOND® technology provides investment protection. We are positive that in the future there will be exciting new developments in temporary adhesives – the standardization of the debonding process ensures that today’s equipment will work with tomorrow’s adhesives.
EV Group has opened its application labs in Europe, US and Asia for all parties in the thin wafer ecosystem to provide the infrastructure for adhesive development and qualification on the newest equipment generation. We have developed a standardized qualification procedure for new adhesives. We evaluate temperature capability of adhesives by thermal treatment of bonded wafers instead of open surface TGA measurements as even very little outgassing in the bond interface can result in thin wafer defects. The coating uniformity and edge bead are qualified pre- and post bonding. The adhesive’s ability to enable ultra thin wafer thinning is qualified by post thinning TTV measurements and thin wafer edge quality assessment. In regards to high volume manufacturing the cycle time of edge zone release and edge zone debond processes is determined. Figure 4 shows the temperature capability of various high temperature materials. We have qualified various adhesives for the high temperature processing range up to 320°C specifically targeting power device manufacturing. For memory applications a key criterion is to keep the bonding temperature well below 200°C. Due to the described standardized debonding process and standardized equipment it is now possible to develop and implement application specific adhesives.
The availability of carrier wafers is another important aspect for a reliable and versatile supply chain. EV Group enables its customers to manufacture the ZoneBOND® carrier by themselves. For pilot line and low volume production the carrier preparation modules are integrated into the EVG850TB temporary bonding system. For high volume manufacturing a dedicated ZoneBOND® carrier manufacturing system is provided. Standard silicon or glass wafers can be used as carrier wafers, which gives long term cost clarity.g system. For high volume manufacturing a dedicated ZoneBOND® carrier manufacturing system is provided. Standard silicon or glass wafers can be used as carrier wafers, which gives long term cost clarity.
Figure 4: Various adhesives with high temperature capability