by Françoise von Trapp, managing editor, Advanced Packaging
Oct. 21, 2008 – Throwing its hat in the ring with a host of semiconductor companies (R&D labs, fabs, foundries, equipment/material manufacturers, IP companies, and packaging houses) in search of low-cost 3D integration processes, Ziptronix Inc. revealed technical details on its direct bond interconnect technology (DBI), which is said to enable low-cost wafer-to-wafer or chip-to-wafer bonding without high-temperature compression.
Companies and consortiums have been lining up with processes to solve different parts of the equation for some time, such as with the EMC3D Consortium’s achievement of a via-first process flow for TSVs at $189/wafer. Dan Donabedian, CEO, Ziptronix, says he has observed a growing consensus across the semiconductor supply chain that a low-cost high-throughput, reliable bonding process is necessary to bring 3D IC integration into the mainstream. What is well-established, he noted, is that TSVs are going to be part of any large-scale 3D IC process, and that metal-to-metal bonding offers clear advantages. Ziptronix’s contribution is what Donabedian defines as the final part of the equation; a high-throughput, low-temperature oxide bond technology that achieves a metal connection without requiring low-throughput, high-temperature thermal compression.
In a comparison study done by Yole Développment, DBI proved to have a lower bonding cost per wafer than either copper-to-copper thermocompression or adhesive bond process. For a typical fab running 500,000 300mm wafers per year using 1×20μm vias, the bonding costs/wafer level (including CMP) were: $57 for Cu-Cu, $22 for adhesive, and $12 for DBI. Addressing the latter, Chris Sanders, Ziptronix’ director of business development, cited several key elements to cost savings with the company’s proprietary Zibond and DBI processes, including use of nickel as an interconnect metal; elimination of thermocompression and its associated tool requirements (bond chambers, thin wafer/die handling); increased throughput due to reduced cycle time (no adhesive, pressure, or temperature requirements); and the ability to batch process.
Cost per wafer level for different bonding technologies. (Source: Ziptronix/Yole Développement)
Sanders explained that batch processing can’t be done with thermo-compression because of the need for heat. However, the Zibonding oxide bonding process allows wafers to be bonded at room temperature and stored before completing the final interconnect processes; “then in DBI you add heat to achieve the electrical connection between the nickel pads.” The processes accommodate TSVs, but interconnects can be achieved without them, he added.
Initially developed as a way to assemble 3D subsystems (by bonding and interconnecting bare die directly onto a board-mountable substrate), it was a technology whose market was not yet ready for it. However, the market has now caught up, according to Donabedian, citing a demographic shift in attendees at 3D symposiums and conferences — rather than engineers, he’s noticing more business development and marketing executives in the audience, as they educate themselves on these technologies.
Military contractors have been the first to incorporate Zibond and DBI, and Sanders identified CMOS image sensors, focal plane arrays (FPAs), and memory-logic stacks as the next target applications. Although Ziptronix is not part of any consortium targeting 3D integration processes, Sanders and Donabedian said the company is working with tool vendors such as EV Group and Suss MicroTec to enable their technology, and have formed an affiliation with Tezzaron to establish roadmaps for 3D stacked memory.
While most industry analysts still point to 2011 for TSV production, Donabedian predicts earlier adoption in mid-2010. “Those who want to take the lead in the market will find the value-add,” he noted. The logistics chain is different from 12 months ago, when foundries and customers were tossing technology limitations back and forth, he explained. He says he now he sees them working together to understand the dynamics, and that most of the end customers have roadmaps for 3D.
Despite the downturn in the economy, Donabedian is enthusiastic about bringing Zibond and DBI to market, because companies are interested in new technologies that might give them an advantage. “They are opening their doors to Ziptronix right now,” he says. “The timing is perfect.” — F.v.T.