By Mark LaPedus
GlobalFoundries has announced several milestones in the 2.5D/3D chip arena–a series of events that brings the technology one step closer to mass production.
On the 3D front, GlobalFoundries has produced its first functional 20nm silicon wafers with integrated through-silicon vias (TSVs). At its Fab 8 facility in Saratoga County, N.Y., the silicon foundry vendor manufactured TSV test wafers using its 20nm-LPM process technology.
At the same time, the company also demonstrated a 32mm x 26mm interposer test vehicle for 2.5D chips. For some time, it has been developing a 65nm interposer manufacturing line within its Fab 7 complex in Singapore.
These are key steps to enable the eventual production of 2.5D and 3D chips. GlobalFoundries’ next step is to work in conjunction with its chip-assembly partners. At some point in the future, the OSATs will take the TSV-enabled wafers and then assemble and qualify 3D test vehicles for customers.
GlobalFoundries is making progress on other fronts. It is taping out a 3D design for an undisclosed customer and is working with two others on 2.5D. “2.5D is already here,” said David McCann, vice president of packaging technology at GlobalFoundries. “Our industry has been talking about the promise of 3D chip stacking for years, but this development is another sign that the promise will soon be a reality.”
Other foundries, including IBM, Samsung, Tezzaron, TSMC and UMC, are also ramping up or developing their respective 2.5D/3D capabilities. But advanced chip stacking has several challenges and is still a few years away from mass production. Some estimate that volume production won’t occur until 2014 or 2015.
E. Jan Vardaman, president of TechSearch International, said the ability to obtain stacked memory is one of the stumbling blocks for 3D designs. Devices based on the Wide I/O-2 standard are not due out until 2014 or 2015. “Everyone is waiting for the memory cubes,” Vardaman said. “The main question is when are the memory cubes going to ship?”
There are other issues as well. “I think that a number of people are trying out new materials to handle the bond/debond step. That takes more time,” she said. “Many companies indicated they still needed floor planning tools.”
Cost, of course, is still a factor. “Once the technology issues are resolved, the industry will need to bring up the yields in order to lower the cost,” she added.
Still, GlobalFoundries is moving full speed ahead in the arena. Last year, the company entered the 2.5D/3D chip-stacking foundry market and began to install the production tools within its Fab 8 complex.
Now, the company has developed the first 20nm silicon with TSVs, which measure 6u in diameter and 60u deep. “Our integration strategy works for TSV,” McCann said. It is also obtaining good results and yields with its silicon interposer technology in Singapore, he added.
GlobalFoundries’ strategy is far different than TSMC and Samsung, both of which are offering turnkey solutions. In contrast, GlobalFoundries will handle the traditional front-end steps and the “via creation” process. Then, the foundry vendor will hand off the traditional backend steps—such as temporary bonding/debonding, grinding, assembly and test—to the third-party packaging houses.
GlobalFoundries’ strategy, according to McCann, is more flexible and has more advantages over the turnkey model. “Our supply chain is an open model,” he said.
Like its rivals, GlobalFondries utilizes a “via-middle” approach to TSV integration. To overcome the challenges associated with the migration of TSV technology from 28nm to 20nm, the company has developed a proprietary contact protection scheme. This scheme enables the company to integrate the TSVs with minimal disruption to the 20nm-LPM platform technology, demonstrating SRAM functionality with critical device characteristics in line with those of standard 20nm-LPM silicon.